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High penetration of distributed generation (DG) is evident in the development of modern power systems, and this trend is expected to continue growing. Grid integration control strategies have been recognized as the main way to save investment, reduce fossil fuel energy consumption, and improve the reliability and flexibility of power systems. The distribution network itself is also a weak link that causes the deterioration of power quality and affects the overall performance and efficiency of the system. Therefore, smart distribution networks play a decisive role in the overall concept of the smart grid. Smart inverter control is more appreciated in the field of optimal operation of low voltage distribution networks with high penetration of distributed generations, due to its advantages of high flexibility, quick response time and low additional system cost. The work presented in this PhD thesis aims to investigate the impact of high penetration of distributed energy resource in the power system and develop a multi-objective optimisation method to improve the distributed network performance. This research studied the impact of the access of a large number of distributed energy sources such as rooftop solar photovoltaics on low carbon power availability and quality of supply within the distribution network. By looking for the best model composition, it created a distribution network model with highly distributed photovoltaics. The optimized maximum capacity and location of the solar energy configuration in the distribution network are realized through voltage sensitivity and genetic algorithm. The concept of adjusting reactive power output in distribution network to affect system characteristics are based on the smart inverter functions of distributed photovoltaics. To further conduct the multi-objective control, this thesis proposed an adaptive particle swarm optimisation scheme. The main algorithm based on multi-objective particle swarm optimization (MOPSO) algorithm, which uses the concept of Pareto dominance to find solutions for multi-objective problems. Through the investigation of the interactions of multiple effects such as voltage fluctuations, system cost and CO2 emissions in a distributed network with saturated PV penetration, with the advanced algorithm in planning photovoltaics and further smart inverter volt/var control scheme, the generation cost and GHG emission curve were improved and avoid the disturbance to customer behaviours. This thesis also proposed an adaptive multi-objective control scheme for distribution networks with photovoltaics infeed, on the basis of smart inverter control. To cater for the fact that low voltage distribution network may face problems such as voltage mitigation, system loss increase and customer also requires to pay less bill. The method is designed to solve these multiple conflict objectives. The correctness and validity of the proposed strategy are verified by numerical examples in a radial large 149 bus system. This thesis conducted detailed investigation of highly distribution network characteristics and proposed a process of multi-objective control scheme for the distribution network. It not only illustrated the control method, but also included the implementation requirement and consideration beforehand and afterwards. In addition, unlike mostly previous work, the work presented in this thesis included benefits of users as one of the optimisation goals. Therefore, this work can be adopted and applied by DSO as a technical reference and for trade-off decision makings in a highly distributed energy network.

Organic and hybrid perovskite solar cells offer a cost-effective and efficient alternative to traditional silicon solar technologies. Also, the tunability of these photoactive materials allows for devices to be crafted for bespoke purposes, such as tandem solar cells or for harvesting energy from indoor lighting. The work in this thesis presents the development, understanding, and application of these materials. First, the development of two new small molecule materials for organic solar cell application is discussed. Their solar cell performance is optimised using several techniques to control the organic semiconductor film morphology and changes to the film are characterised using atomic force microscopy. The stability of these new solar cells is then measured in ambient conditions under constant illumination, which is correlated to the film morphology. Then the electron mobility of two high-performing non-fullerene organic materials using a Time of Flight method is measured. This technique not only allowed for the accurate measurement of the electron mobility of these materials, but also provides insight into the disorder of the organic film and the existence of deep-traps within. Lastly, a hybrid perovskite solar cell is optimised for application in visible light communications for simultaneous energy and data harvesting. In this study the devices are measured under various illumination conditions to gain insight into their loss mechanisms, while also optimising them for this specific purpose.

Electricity generation from fossil fuel-based technology is considered to be one of the major sources of greenhouse gases in the world. For this reason, some environmental policies have been enacted to encourage electricity generators to seek alternatives in generating clean, affordable and reliable electricity. This has led to the emergence of low carbon technologies such as wind and solar in the power system. This development poses two major challenges in the system; 1) how to accommodate the increasing level of uncertainty in the network. 2) The high cost of upgrading the transmission network to accommodate the capacity of renewable energy in the system. Building new transmission networks is capital-intensive as shown, by the 2014 Ten-year Network Development plan of the European Network of Transmission System Operators for Electricity (ENTSO-E), where about 150 billion euros will be needed to integrate up to 60% of renewables by 2030. The traditional transmission expansion planning (TEP) approach is no longer suitable in today's system as it lacks flexibility and is considerably expensive. Therefore, transmission planners must develop cost effective and flexible strategies to utilise network assets while minimising the spillage of renewable generation. In this thesis, three different flexible control options namely, demand response, electrical energy storage and generation re-dispatch are integrated into the transmission expansion process for evaluation. The evaluation is implemented by comparing the TEP models with and without the flexible control options. In the first study a new comparison tool known as transmission expansion cost-reliability (TECR) plane is used to measure the goodness of the proposed transmission expansion plans with and without electrical energy storage. In another study, stochastic TEP models with energy storage and generation re-dispatch are evaluated against the traditional planning approach considering different levels of solar energy penetration at each stage of the transmission expansion planning. Furthermore, a TEP model with demand response aggregation is also proposed. In this model, uncertainty in the amount of demand response provided by aggregators is modelled using a new approach that is based on expected utility theory and certainty equivalent. The results obtained from these studies show that significant economic benefits can be derived by planning the network with theses flexible control options.

The use of battery energy storage system (BESS) in the electricity grid is growing in popularity as a major player in facilitating the integration to greater levels of renewable energy sources (RES) into the electricity network. Photovoltaic (PV) in particular, has seen the highest increase in deployed capacity in recent years as a result of falling costs. However, high levels of penetration of PV into the network, can lead to technical challenges such as harmonics, flickers, reverse power and overvoltage. Among these challenges, overvoltage constitutes the major limitation to the increase in RES penetration. Overvoltage can be managed through adequate utilisation of BESS on the network, but BESS are still expensive. Because the health and lifespan of a BESS is dependent on the way it is cycled during its operating life, it is important that BESS is operated in a way that promotes its longevity. This thesis proposes strategies for the coordination of operations of multiple BESS in networks with high penetration of PV. It presents techniques for mitigating resultant overvoltage situations, while operating the BESS in ways that maximise their lifespans. Control strategies used are based on the use of voltage sensitivities of the network buses for the estimation of charge and discharge powers of the participating BESS at different times. The flat structure sensitivity scheme (FSSS) is the basic coordination scheme that considers the entire network in a flat non-heirarchical structure. The neighbourhood schemes include the uniform neighbourhod participation scheme (UNPS) and the rotational neighbourhood participation scheme (RNPS). These neighbourhood schemes involve the segmentation of the network into neighbourhoods to promote more effective participation of the BESSs. In this thesis, implementation of the schemes on different networks was carried out and simulation results also presented. The results demonstrate that with the proposed strategies, BESS can be effectively used to achieve higher levels of penetration of PV in the power networks, while maximising the BESS lifetime.

Photovoltaic devices have an efficiency limit of 33% set by fundamental loss processes in the semiconductor materials. The largest loss comes about as a result of charges excited far above the bandgap losing their excess energy as they cool to the bandedge, a process known as thermalisation. Carrier multiplication offers a means of reducing thermalisation losses using a system in which excess energy from one electron-hole pair is transferred to produce a second electron-hole pair. Fully harnessing carrier multiplication would raise the efficiency limit of photovoltaic devices to 44%. Typically, various challenges mean the benefits of carrier multiplication have not yet been realised. In quantum dot materials, the fundamental understanding of the carrier multiplication process is still lacking. A more thorough understanding of the cooling and recombination mechanisms is needed to fully exploit this phenomenon. In organic materials, an excited singlet exciton splits to form two triplet excitons on neighbouring molecules. The process in organics is referred to as singlet fission. Producing a device that can make use of the singlet fission process however, has proved difficult, limited in part by the instability of singlet fission materials and also by challenges brought about by the need to couple to another material. In this thesis, we will examine both quantum dot and organic systems. The initial work in this project involved the fabrication of quantum dot devices. Steps were taken to improve the efficiency and reproducibility of the devices with the aim of investigating carrier multiplication in device stacks. However, the devices work showed limited success and the decision was taken to move to ultrafast spectroscopy. In examining quantum dot films using picosecond transient absorption spectroscopy, we found clear signatures of carrier multiplication occurring in films of dots synthesis here. We also found that some of our results were at odds with explanations in the literature. To explain our results, we took data under a range of excitation conditions and compared them to the predicted results of various explanations in the literature. We also used ultrafast spectroscopy to examine singlet fission in diketopyrrolopyrrole-based molecules. Such molecules are much more stable than the polyacenes typically used in singlet fission research. We looked for the slow recombination signature of triplet excitons in films of a diketopyrrolopyrrole-based molecule using transient absorption spectroscopy. We assigned the formation mechanism of these triplet molecules using the timescale of the singlet to triplet transition. In this work, we have considered means of increasing the harvestable energy from photovoltaic devices and improved our understanding of how such efficiency increases may be possible.

The research presented in this thesis aims to enhance understanding of the influence of the inherent variability of solar irradiance on nationwide photovoltaic (PV) system performance. The spatial and temporal consistency of the solar resource is investigated. The case study area is the UK and the body of work presents nine publications written over four years with this objective in mind. The key research theme is to produce national solar resource maps from ground-based measurements of solar radiation. Geographical Information System (GIS) techniques are utilised to build a UK map of irradiation from geographically sparse data, requiring development of new tools to both generate and verify the map data. With an augmented understanding of the solar resource, PV system dispersal is then investigated, allowing analysis and prediction of the impact on the electrical grid. The papers describe: (1) determination of the most appropriate algorithm for interpolating ground-based irradiation measurements in the UK to countrywide coverage; (2) selection of solar irradiance component separation and translation models to obtain plane-of-array irradiation from the weather station global horizontal records; (3) justification of weather stations data as a fundamental model input; (4) statistical analysis of LiDAR data and application of GIS models to LiDAR data to obtain PV system tilts and azimuths as model inputs for (2); (5) conversion of solar irradiation to electrical output; (6) shading effects; (7) study of geographic divergence of generation; (8) aggregate grid variability; and (9) future installation scenarios. There has been no previous study which commences with obtaining irradiation values for PV and proceeds through the entire modelling chain to assess cumulative impacts on grid transformers. This study may be adapted as a guide when undertaking equivalent research in other countries. Specifically, the work presented here is more extensively validated than that of previous authors. A nationwide analysis of spatial and temporal variation of PV output is delivered and current and future impacts on the National Grid are taken into consideration.

To date optoelectronic devices have been dominated by inorganic semiconductors such as silicon and gallium nitride. However organic semiconductors have many potential advantages and have shown significant research progress in both organic light-emitting diodes and organic photovoltaics. Tightly-bound excitons form intermediate states in the operation of both organic light-emitting diodes and organic photovoltaics. Many properties of an exciton are determined by its spin state, which can either be a spin-zero singlet or a spin-one triplet. In both organic light-emitting diodes and organic photovoltaics triplet excitons can be a source of loss due to poor radiative coupling to the ground state and energy loss on formation from the singlet state. In this thesis, methods of avoiding loss pathways through triplet states are investigated in both organic light-emitting diodes and organic photovoltaics. Carbene-metal-amides are a new class of emitter material for organic light-emitting diodes. High-performance devices are reported with maximum external quantum efficiency of 27%, which indicates effective triplet utilisation. Emission colour can be selected through both molecular design and host environment allowing the demonstration of blue-emitting devices with 19% external quantum efficiency. Host-free devices have been fabricated with record external quantum efficiency of 23%, enabled by a resistance to concentration-dependent luminescence quenching. Electron spin resonance has been used to investigate the mechanism of intersystem crossing between singlets and triplets in the important organic light-emitting diode material, 4CzIPN. It is demonstrated that the spin-vibronic model of intersystem crossing breaks down in device-relevant solid films. Evidence is instead found for back transfer from a spin-correlated radical pair state being the dominant mode of intersystem crossing. With increased film concentration the signal becomes dominated by free polarons, suggesting that charge separation may be a mechanism of luminescence quenching at high concentration. In many organic photovoltaic material systems triplets are low-lying states from which charge separation is not energetically favoured. In this thesis, attempts are made to negate this triplet loss pathway by the use of low singlet-triplet energy gap materials to ensure that the charge-transfer state can be endothermically accessed from all molecular exciton states.

The results described in this thesis concern the design, synthesis and characterisation of new candidate absorber layer sensitizer materials for photovoltaic cells; in particular exploring novel halometallate hybrid structures. Through this work, the field of iodoantimonate and iodobismuthate hybrid materials has been expanded with the discovery and analysis of many novel structures. Alternative, lead-free, antimony and bismuth metal containing hybrid structures are key and of much interest in the rapidly developing area of perovskite-based solar cell architectures. The work undertaken has added to building the database and thus further developing the understanding of hybrid absorber materials with the overarching aim of progressing towards real world thin-film and tandem solar cell designs to challenge and expand upon the industry dominant silicon-based solar cell architectures of today. An introduction to the field and the context of the research is given in chapter 1, and the relevant experimental techniques are discussed in chapter 2. The remaining chapters of the thesis present the findings of the project as detailed below. The particular focus of the work carried out covers the discovery and study of the structure and properties of over ten novel iodoantimonate and twenty novel iodobismuthate hybrid materials. The results of the investigations carried out are presented in an alternative thesis format with two full published papers integrated within the narrative in chapter 3. Additionally, as detailed in chapter 4 an in-situ alkylation solvothermal synthetic technique used in the formation of more complex templating agents was found and used to great effect throughout the synthesis and study of iodoantimonate and iodobismuthate novel halometallate hybrid materials. Moreover, a promising opening for a new avenue of perovskite structure potential was uncovered; triggered by the discovery and preliminary analysis of an unfamiliar novel three-dimensional superoctahedra-octahedra linked halometallate motif described in chapter 5. Outside of this, work was undertaken on other alternative candidate material areas such as bismuth-based coordination complexes, bismuth sulphide iodide, double perovskites and related structures; contained within chapter 6. To finish, the overall results and thesis conclusions are discussed in chapter 7.

This thesis contributes to improve the photovoltaic Distributed Generation (DG) systems by proposing three novel methods to the system. On DC conversion side, a new integrated magnetic structure for interleaved converter and a new method to calculate the eddy current and hysteresis losses in the magnetic core were proposed. On inversion side, A new synchronisation method for grid tie inverters was suggested. The technique is using the Recursive Discrete Fourier Transform (RDFT) to find fundamental in grid waveform. On the DC converter side, the benefits of the new structure is to produce magnetic flux that alternate in the core across both directions of the BH curve. The advantages of alternating magnetic flux are, to increase the Root Mean Square (RMS) value of produced current with respect to core volume that lead to reduce the core size and reducing losses by using high permeability material. Furthermore, the proposed structure led to reduce the number of magnetic components which helped to improve the efficiency. The converter was tested and evaluated were the results show that the topology is able to produce high gain and it shows that the new interleaved structure is efficient. A new method to calculate the eddy current loss was proposed, where the flux waveform in the core was analysed to its original frequency component. Each of the components were utilized individually to find the loss. The effect of changing the duty cycle of the converter was taken into consideration on the total eddy current loss, as it will effect on the total harmonics content in the flux waveform. On the inverter side, due to recent developments combined with the increasing power demand by single phase non-linear loads where voltage spikes, harmonics and DC component were impacted the electric grid quality. These effects can likewise make the synchronisation process a challenge, where filters or Digital Signal processing (DSP) analysers are required to acquire the fundamental component as a consequence to the waveform deformation. A new linear approximation with RDFT is presented in this thesis for grid tie inverters. The new method provides a computation reduction as well as high accuracy in tracking the fundamental frequency in a distorted grid during synchronisation. The method accuracy was proved mathematically and simulated with different input signals. Error in magnitude and frequency measurement were measured, presented and compared with other research in order to verify the proposed method.

Electroluminescence (EL) imaging is a fast and comparatively low-cost method for spatially resolved analysis of photovoltaic (PV) devices. A Silicon CCD or InGaAs camera is used to capture the near infrared radiation, emitted from a forward biased PV device. EL images can be used to identify defects, like cracks and shunts but also to map physical parameters, like series resistance. The lack of suitable image processing routines often prevents automated and setup-independent quantitative analysis. This thesis provides a tool-set, rather than a specific solution to address this problem. Comprehensive and novel procedures to calibrate imaging systems, to evaluate image quality, to normalize images and to extract features are presented. For image quality measurement the signal-to-noise ratio (SNR) is obtained from a set of EL images. Its spatial average depends on the size of the background area within the EL image. In this work the SNR will be calculated spatially resolved and as (background independent) averaged parameter using only one EL image and no additional information of the imaging system. This thesis presents additional methods to measure image sharpness spatially resolved and introduces a new parameter to describe resolvable object size. This allows equalising images of different resolutions and of different sharpness allowing artefact-free comparison. The flat field image scales the emitted EL signal to the detected image intensity. It is often measured through imaging a homogeneous light source such as a red LCD screen in close distance to the camera lens. This measurement however only partially removes vignetting the main contributor to the flat field. This work quantifies the vignetting correction quality and introduces more sophisticated vignetting measurement methods. Especially outdoor EL imaging often includes perspective distortion of the measured PV device. This thesis presents methods to automatically detect and correct for this distortion. This also includes intensity correction due to different irradiance angles. Single-time-effects and hot pixels are image artefacts that can impair the EL image quality. They can conceivably be confused with cell defects. Their detection and removal is described in this thesis. The methods presented enable direct pixel-by-pixel comparison for EL images of the same device taken at different measurement and exposure times, even if imaged by different contractors. EL statistics correlating cell intensity to crack length and PV performance parameters are extracted from EL and dark I-V curves. This allows for spatially resolved performance measurement without the need for laborious flash tests to measure the light I-V- curve. This work aims to convince the EL community of certain calibration- and imaging routines, which will allow setup independent, automatable, standardised and therefore comparable results. Recognizing the benefits of EL imaging for quality control and failure detection, this work paves the way towards cheaper and more reliable PV generation. The code used in this work is made available to public as library and interactive graphical application for scientific image processing.

This research is concerned with the drivers to utilize Renewable Energy in Gulf Cooperation Council countries with a focus on Kuwait. Such countries show high rates of electricity subsidies with high rate of emissions. At present, there is a continuous need to build new power stations to increase the electrical capacities, in order to cover the high peak loads that occurs in summers to avoid blackouts. The aim of this research is to create a combination of approaches to assess the adoption (economic and environmental) of Photovoltaic for electricity generation in Kuwait, which can be used to assist policy makers to compare various energy mixes and hence determine whether their current and future strategies are appropriate. Kuwait is in this research representative of an exemplar of oil-based economy in Gulf Cooperation Council region since they share similar energy policies and geographic location. The research provides an insight into the adoption of renewables in the region and the impact that particular energy mixes may have. Nine future potential scenarios are created showing different levels of PV deployment within Kuwait. The combination of approaches in this research estimates the economic and environmental impacts using Levelized Cost of Electricity and Life Cycle Assessment respectively of differing RE mixes. The findings show that energy storage increases the cost of electricity and the emissions from the photovoltaic sector. However, for the energy mix (PV and conventional), assuming oil price greater than 10.1$/Bbl. (when no storage required) and 15.2$/Bbl. (when using storage), PV generally lowers the cost of electricity, CO2 and SO2 emissions. Whilst, human toxicity is increased when storage is used. Taking all these factors into account, PV deployment is generally beneficial. However, if different combinations of impacts are considered, environmental and economic impacts may take different patterns. This led to a multi-objective problem to be solved. Using Pareto Front analysis, scenarios without storage requirement (i.e. 13% or less of photovoltaic) are preferable if only cost and human toxicity are considered. The contribution to knowledge from this research is that the deployment of large scale PV technology is beneficial in Kuwait economically and environmentally at least until 30% of the maximum peak load of electricity. The results have implications for other GCC countries with similar geographical, political and energy drivers; the methodology used in this research would be appropriate for these contexts.

The increased penetration of residential-scale photovoltaic (PV) systems in European-style low voltage (LV) networks (i.e., long feeders with high number of connected customers) is leading to technical issues such as voltage rise and thermal overload of the most expensive network assets (i.e., transformer, cables). As these issues significantly limit the ability of LV networks to accommodate higher PV penetrations, Distribution Network Operators (DNOs) are required to proceed with expensive and time-consuming investments in order to reinforce or replace these assets. In contrast to this traditional approach of network reinforcement, which potentially leads to massive capital expenditure, the transition towards active LV networks where controllable elements, existing (i.e., PV systems) and likely to be adopted (i.e., battery energy storage systems, LV on-load tap changer transformers), can be managed in real-time, poses an attractive alternative. Although several active network management schemes have been recently proposed to increase the hosting capacity of PV-rich LV networks, they are mostly based on managing voltage issues only; and, in general, aim to solve technical issues separately. Integrated solutions aiming at managing simultaneously voltage and thermal issues are required, as recent studies demonstrate that both issues can coexist in PV-rich LV networks. More importantly the majority of studies, which commonly neglect the characteristics of real LV networks (e.g., unbalanced, three-phase, radial, multiple feeders with several branches, different types of customers), use complex optimisation techniques that require expensive communication infrastructure and extensive or full network observability (currently not available in LV networks). However, considering the extensiveness of LV networks around the world, practical, cost-effective and scalable solutions that use limited and already available information are more likely to be adopted by the industry. Considering the above gaps in the literature, this Thesis contributes by proposing innovative and scalable active network management schemes that use limited network monitoring and communication infrastructure to actively manage (1) Residential-scale PV systems, (2) Residential-scale Battery Energy Storage (BES) systems and (3) LV on-load tap changer (OLTC)-fitted transformers. The adoption of the proposed active network management schemes, which makes use of already available devices, information and requires limited monitoring (i.e., secondary distribution substation), allows making the transition towards active LV networks more practical and cost-effective. In addition, to tackle the challenges related to this research (i.e., lack of realistic LV network modelling with high resolution time-series analyses), this Thesis, being part of the industrial project 'Active Management of LV Networks' (funded by EDF R&D) and having access to French data, contributes by considering a fully modelled typical real residential French LV network (three-phase four-wire) with different characteristics and number of customers. Moreover, realistic (1-min resolution) daily time-series household (from real smart meter data) and PV generation profiles are considered while a stochastic approach (i.e., Monte Carlo) is adopted to cater for the uncertainties related to household demand as well as PV generation and location.

Concentrating photovoltaic (CPV) systems are a key step in expanding the use of solar energy. Solar cells can operate at increased efficiencies under higher solar concentration and replacing solar cells with optical devices to capture light is an effective method of decreasing the cost of a system without compromising the amount of solar energy absorbed. CPV systems are however still in a stage of development where new designs, methods and materials are still being created in order to reach a low levelled cost of energy comparable to standard silicon based photovoltaic (PV) systems. This work outlines the different types of concentration photovoltaic systems, their various design advantages and limitations, and noticeable trends. Comparisons on materials, optical efficiency and optical tolerance (acceptance angle) are made in the literature review as well as during theoretical and experimental investigations. The subject of surface structure and its implications on concentrator optics has been discussed in detail while highlighting the need for enhanced considerations towards material and hence the surface quality of optics. All of the findings presented contribute to the development of higher performance CPV technologies. Specifically high and ultrahigh concentrator designs and the accompanied need for high accuracy high quality optics has been supported. A simulation method has been presented which gives attention to surface scattering which can decrease the optical efficiency by 10-40% (absolute value) depending on the material and manufacturing method. New plastic optics and support structures have been proposed and experimentally tested including the use of a conjugate refractive-reflective homogeniser (CRRH). The CRRH uses a reflective outer casing to capture any light rays which have failed total internal reflection (TIR) due to non-ideal surface topography. The CRRH was theoretically simulated and found to improve the optical efficiency of a cassegrain concentrator by a maximum of 7.75%. A prototype was built and tested where the power output increase when utilising the CRRH was a promising 4.5%. The 3D printed support structure incorporated for the CRRH however melted under focused light, which reached temperatures of 226.3°C, when tested at the Indian Institute of Technology Madras in Chennai India. The need for further research into prototyping methods and materials for novel optics was also demonstrated as well as the advantages of broadening CPV technology into the fields of biomimicry. The cabbage white butterfly was proven to concentrate light onto its thorax using its highly reflective and lightweight wings in a basking V-shape not unlike V-trough concentrators. These wings were measured to have a unique structure consisting of ellipsoidal pterin beads aligned in ladder like structures on each wing scale which itself is then tiled in a roof like pattern on the wing. Such structures of a reflective material may be the answer to lightweight materials capable of increasing the power to weight ratio of CPV technology greatly. Experimental testing of the large cabbage white wings with a silicon solar cell confirmed a 17x greater power to weight ratio in comparison to the same set up with reflective film instead of the wings. An ultrahigh design was proposed taking into account manufacturing considerations and material options. The geometrical design was of 5800x of which an optical efficiency of either ~75% with state of the art optics should produce and effective concentration of ~4300x. Relatively standard quality optics on the other hand should give an optical efficiency of ~55% and concentration ratio ~3000x. A prototype of the system is hypothesised to fall between these two predictions. Ultrahigh designs can be realised if the design process is as comprehensive as possible, considering materials, surface structure, component combinations, anti-reflective coatings, manufacturing processes and alignment methods. Most of which have been addressed in this work and the accompanied articles. Higher concentration designs have been shown to have greater advantages in terms of the environmental impact, efficiency and cost effectiveness. But these benefits can only be realised if designs take into account the aforementioned factors. Most importantly surface structure plays a big role in the performance of ultrahigh concentrator photovoltaics. One of the breakthroughs for solar concentrator technology was the discovery of PMMA and its application for Fresnel lenses. It is hence not an unusual notion that further breakthroughs in the optics for concentrator photovoltaic applications will be largely due to the development of new materials for its purpose. In order to make the necessary leaps in solar concentrator optics to efficient cost effective PV technologies, future novel designs should consider not only novel geometries but also the effect of different materials and surface structures. There is still a vast potential for what materials and hence surface structures could be utilised for solar concentrator designs especially if inspiration is taken from biological structures already proven to manipulate light.

The world population is following an increasing growth than ever. This is accompanied by the modern life style with increased demand for energy in order to facilitate the daily life routines. Among the energy sources, especially the renewable ones, harnessing the solar radiation is considered as an everlasting power source and less utilised so far. Solar cells have been used as a useful mean for converting the photons that presents in the sun light, into electricity. As there exist many types of the solar cells and the current trend of publication focuses on perovskite solar cells, the work interest of this thesis was generally paid to this type. The vast majority of published work in the literature was devoted to using n-type semiconductors in fabricating perovskite solar cells, thus less attention was paid to p-type counterpart. Hence, different work is conducted in this thesis toward producing several perovskite solar cell devices at low prices with moderate efficiencies. This thesis contains 10 chapters starting with an introduction and a general literature review in the first chapter, while a brief description of the deposition and characterisation methods are discussed in chapter 2. Excitonic solar cells are represented in this thesis by dyesensitised solar cells (DSSCs) and perovskite solar cells (PSCs), and are shown in five chapters which are designed in a way to make it easier to follow, each chapter has the literature review, the aim of the work, experiments and discussion of the results then a conclusion. A conclusion regarding the conducted projects is driven in chapter 8 with suggestions for future work in the same chapter. Chapter 9 deals with the dissemination of the results, while chapter 10 has the references list.

Measurement uncertainty is an indication of the quality of a given measurement and ultimately translates into the confidence with which a decision can be made. In the context of PV, measurement uncertainties propagate into energy yield uncertainty, which in turn culminates into financial risk associated with an investment. This risk increases the cost of a PV installation. The aim of this thesis is to contribute towards the reduction of PV related measurement uncertainties. This is done in two ways. One is via developing and utilising more comprehensive methodologies for uncertainty propagation of complex measurands. The other is via more detailed estimates of the uncertainty contributors. In particular, the areas addressed in this thesis are the uncertainty estimation of the temperature coefficient measurements of modules; the uncertainty estimation of energy rating and module performance ratio measurements; and the uncertainties due to spectral effects on measurements performed with a flash solar simulator. The reported deviation in measurements of the temperature coefficients of P_MAX of modules is in the order of ±10% to ±15%. This is larger than the difference in the temperature coefficients of modules of the same type. The first step to improving the deviation between measurements is to estimate the uncertainty in a robust way. It was identified that there was no accepted approach of doing this. These measurements are strongly correlated, which complicates the uncertainty estimates. For the sake of simplicity, previously correlations have been avoided and conservative estimates used instead. In this work, uncertainties in both temperature and power and their correlations are estimated and propagated into the overall temperature coefficient uncertainty. Furthermore, temperature coefficients were calculated via weighing the measurements with their associated uncertainties. This was done for five different measurement setups that represent the majority of setups used worldwide. The approach was validated with measurement intercomparison of two modules measured on all systems. The approach reduced the overall uncertainty by half compared to the previous conservative estimates. It was demonstrated that uncertainties as low as 3% are achievable. The improved uncertainty estimates enabled the identification of a systematic effect due to a class B spectrum. This work culminated in the lowest reported measurement deviation of ±3.2% for module P_MAXtemperature coefficient measurements that was within the stated measurement uncertainties. The clear benefit of accounting for correlations was extended to measurements at different irradiance conditions and into the calculation of module performance ratio and energy rating. This was done via defining all the correlations between measurements and then propagating them with Monte Carlo simulations. The simulations are done with samples of a multivariate normal distribution with a variance-covariance matrix that corresponds to the estimated measurement correlations. It is demonstrated that both the energy rating and module performance ratio uncertainties strongly depend on the correlation estimates and that they cannot be conservatively overestimated. The module performance ratio uncertainty can be significantly lower than the measurement uncertainty at STC. This is because of the additional knowledge encoded into the selection of the underlying model used for calculating the energy rating. Therefore, the significance of the choice of model in the upcoming standard has been highlighted. It was confirmed that both bilinear interpolation and the proposed climatic datasets could be used for energy rating, but there are some areas that may need further investigation. An alternative way of improving uncertainty estimates and in turn reducing the associated uncertainty is via a more detailed characterisation of the uncertainty sources. A key uncertainty source is due to spectral effects in flash solar simulators. To better quantify this source, a complementary device was built to monitor the spectrum. The device is based on a matrix of photodiodes with commercially available interference filters situated on top and custom designed data acquisition electronics. This device is used in conjunction with the spectroradiometer to estimate the effects of flash-variation on the spectrum, the spectral temporal stability of the flash and spectral uniformity of the simulator and the attenuation masks used for altering the irradiance levels. It was demonstrated that the spectrum changes significantly during the flash and between flashes. While this effect is partially corrected for via the monitoring cell, it introduces additional uncertainty for non c-Si modules. This uncertainty is minimised by changes in the operational procedures. The spectral non-uniformity of the attenuation masks was shown to be significant, i.e. as large as 4%, in the NIR, prompting further investigation of the additional uncertainty for non c-Si modules. In this work, the methodology of estimating and propagating correlations in PV related measurements and the benefits of doing so are demonstrated. It is also highlighted that the uncertainty due to spectral effects goes beyond the uncertainty of spectroradiometer measurements. Finally, it is shown how they can be estimated with a complementary spectral monitor.

This thesis focuses on the study of hybrid perovskites properties for the purposes of photovoltaic applications. During the almost four years PhD project that has lead to this thesis the record photovoltaic efficiency for this technology has in- creased from 10.9% to 22.1%. Such a significant pace of development can be com- pared with few other materials. It is for this reason that hybrid perovsites have at- tracted impressive research efforts. We approached the study of such unique ma- terials using computational ab-initio techniques, and in particular Density Func- tional Theory. We considered different materials, but most of the attention was concentrated on MAPI (CH 3 NH 3 PbI 3 ). The results are divided in three chapters, each exploring a different material prop- erty. The first chapter reports the electronic structure of the material bulk, sur- faces, and other electronic-related properties such as the rotation barrier for the organic component and the Berry phase polarization. The second chapter focuses on the vibrational properties primary employing the harmonic approximation but also extends to the quasi-harmonic approximation. The outcome of these calculations permitted us to calculate theoretical IR and Ra- man spectra which are in good agreement with different experimental measure- ments. The quasi-harmonic approximation was used to calculate temperature dependent properties, such as the Grüneisen parameter, the thermal dependence of heat capacity and the thermal volumetric expansion. The third and last chapter reviews the thermodynamic properties of binary halide compounds. The cobination of ab-initio calculations with the generalised quasi- chemical approximation has allowed to study the stability of mixed composition perovskites. The results certified a set of stable structures that could stand at the base of observed phenomena of photo-degradation of hybrid perovskite based devices. All three chapters have been written to understand the chemical and physical behaviour of hybrid perovskites and to extended and contribute to the under- standing of experimental work.

The design processes for solar photovoltaic (PV) systems is improved to achieve higher reliability and reduced levelised cost of energy (LCOE) throughout this thesis. The design processes currently used in the development of PV systems are reviewed. This review process included embedding the author in a project to deliver four rooftop PV systems which totalled a megawatt of installed generating capacity, which at the time represented very significant system sizes. The processes used in this are analysed to identify improvement potential. Shortcomings are identified in three main areas: safety assurance, design process integration and financial optimisation. Better design process integration is required because data is not readily exchanged between the industry standard software tools. There is also a lack of clarity about how to optimise design decisions with respect to factors such as shading and cable size. Financial optimisation is identified as a challenge because current software tools facilitate optimising for maximum output or minimum cost, but do not readily optimise for minimum levelised cost of energy which is the primary objective in striving for grid parity. To achieve improved design process integration and financial optimisation, a new modelling framework with the working title SolaSIM is conceived to accurately model the performance of solar photovoltaic systems. This framework is developed for grid connected systems operating in the UK climate, but it could readily be adapted for other climates with appropriate weather data. This software development was conducted using an overarching systems engineering approach from design and architecture through to verification and validation. Within this SolaSIM framework, the impact of shading on array and inverter efficiency is identified as a significant area of uncertainty. A novel method for the calculation of shaded irradiance on each cell of an array with high computational efficiency is presented. The shading sub-model is validated against outdoor measurements with a modelling accuracy within one percent. Final verification of the over-arching SolaSIM framework found that it satisfied the requirements which were identified and actioned. The author installed the new CREST outdoor measurement system version 4 (COMS4). COMS4 is a calibrated system which measures 26 PV devices simultaneously. Validation of SolaSIM models against COMS4 found the modelling error to be within the 4% accuracy target except two sub-systems which had electronic faults. The model is validated against PV systems and found to be within the specified limits.

This research investigated the techno-economic feasibility of increasing hours of electricity services on Likoma Island in Malawi; making use of solar photovoltaic and wind power in order to enhance sustainable livelihood. Likoma Island grid is operated independent of the mainland grid; and the island is supplied electricity by diesel generators which are scheduled for only 14 hours per day. The limited hours of electricity supply constrains the delivery of essential services and hinders people from achieving sustainable livelihoods. The research used empirical and modelled data of solar irradiance and hub height wind speed, photovoltaic and wind energy systems costs, diesel-generator operation costs, energy needs, energy use patterns, electricity demand profile, and prevailing socioeconomic conditions. Diesel, photovoltaic, and wind based energy systems feeding the Island s grid; and autonomous photovoltaic and wind energy systems for selected essential institutions were modelled and simulated using the Hybrid Optimization Model for Electric Renewables. Energy system solutions are proposed indicating cost factors and opportunities for the enhancement of sustainable livelihoods. The thesis argues that with the financial resources committed to the prevailing 14-hours supply of electricity by diesel generators, it is feasible to provide Likoma Island with electricity for 24 hours every day by photovoltaic and wind based energy systems. A deployment model which uses excess energy from the modelled photovoltaic and wind power systems to serve non-grid loads and livelihood activities which are difficult to account for when sizing embedded renewable energy systems has been developed. The findings provide cost projections of photovoltaic and wind energy systems relative to diesel generators upon which investment and policy decisions can be made. Microscale wind maps at 10 m, 25 m, 40 m and 50 m have been developed for identification of potential wind turbine sites. Empirical socioeconomic data which are essential for the design of delivery mechanisms for renewable energy systems have been generated. The deployment model proposed by the research gives new insights into holistic ways of enhancing sustainable energy access in low-income communities. The interdisciplinary insights provided by this thesis can be applied in other countries and communities with similar socioeconomic contexts to Likoma Island.

The requirement for affordable, secure and sustainable energy production is a pressing global challenge and the production of electricity with low carbon emissions is crucial. This usually entails large quantities of renewable energy generation, which is intermittent and often highly distributed throughout the electricity supply system. One of the proposed schemes to manage such generation is the smart grid, the transition to which forms the context for this research. The aim is to investigate the effect of certain psychological and social influences on the adoption of technology necessary to enable smart grids, in order to understand the implications for effective energy policy. In particular, the case of photovoltaic (PV) system adoption in the UK is studied. Empirical data detailing PV installations registered for the Feed in Tariff is analysed in order to understand rates of adoption and how they vary across both time and space. This analysis is combined with a review of policy intervention and literature from psychology to understand drivers for adoption among householders. The results from this study are then used to inform the design of an Agent Based Model of technology adoption within the smart grid context. The decision making of householders is modelled using an algorithm based on Social Cognitive Theory. The model is used to simulate different conditions and generate adoption scenarios in order to understand the potential effects of different parameters on adoption rates. In order to combine the analysis resulting from these methods, the multi-level perspective on transition in socio-technical systems is used to understand how a transition to a smart grid could be described and how adoption of PV in the UK under the Feed in Tariff incentive fits into such a transition. The results show that whilst economic incentive policies have had success in some areas adoption is also dependent on many non-financial parameters. Simulations show that the observability of adoption and the perceived inconvenience or urgency of adoption can have dramatic effects on rates of adoption, in some cases outweighing the rational economic effects of financial incentives. The implication for smart grid related policy is that non-financial factors should be taken into account as well as the more typical financial considerations in efforts to encourage adoption of necessary enabling technology by householders. The models developed could be used in further work to examine in detail adoption of other technologies such as smart home energy management systems and the interaction between adoption rates of multiple smart technologies.

This thesis introduces a novel spectral response (SR) measurement technique using polychromatic filters (filters with very broad spectral transmittances) to determine SR of large area PV devices. Conventionally, SR of a photovoltaic (PV) device is determined by illuminating the device under test (DUT) with a series of monochromatic beams at different wavelengths as described in the international standard IEC 60904-8, or beams of limited spectral content using narrow band pass filters or monochromator. One significant problem associated with the application of the narrow band pass filters for a large-area SR measurement is that low light intensity produced on the measurement plane particularly in certain wavelength ranges: the ultraviolet and infrared. This can produce weak signal responses from a tested PV device. In addition, the imperfection of the filter s mounting position can shift the peak wavelength of the filter s transmittance at angle of incidence greater than 10°. This can cause stray light on the measurement plane. The proposed SR measurement method is called the 'polychromatic SR fitting method' or, in short, it is known as the 'polychromatic method'. The advantage of this method is that higher beam intensity can be produced on the measurement plane as a result of large spectral transmittance of the polychromatic filters. This can improve the signal strength of a tested PV device. This new SR measurement method works by comparing the variations in the currents which are measured at different spectra to the currents which are calculated at the same spectral conditions using the SR model. Validations of this method for a large- and small-area SR determinations show that it is potentially feasible as a new technique for determining SR of a PV device with deviations within ±2% across the wavelength bands.

This thesis studies lead suphide (PbS) colloidal quantum dots and their photovoltaic applications. Different sizes of PbS QDs were synthesised and characterised using absorption spectroscopy and transmission electron microscopes. PbS QD Schottky junction devices were fabricated with AM1.5 power conversion efficiency up to 1.8 %. The Schottky junction geometry limits the device performance. A semiconductor heterojunction using ZnO as an electron acceptor was built and the device efficiency increased to 3%. By studying the light absorption and charge extraction profile of the bilayer device, the absorber layer has a charge extraction dead zone which is beyond the reach of the built-in electric field. Therefore, strategies to create a QD bulk heterojunction were considered to address this issue by distributing the junction interface throughout the absorber layer. However, the charge separation mechanism of the QD heterojunction is not clearly understood: whether it operates as an excitonic or a depleted p-n junction, as the junction operating mechanism determines the scale of phase separation in the bulk morphology. This study shows a transitional behaviour of the PbS/ZnO heterojunction from excitonic to depletion by increasing the doping density of ZnO. To utilise the excitonic mechanism, a PbS/ZnO nanocrystal bulk heterojunction was created by blending the two nanocrystals in solution such that a large interface between the two materials could facilitate fast exciton dissociation. However, the devices show poor performance due to a coarse morphology and formation of germinate pairs. To create a bulk heterojunction where a built-in electric field could assist the charge separation, a TiO2 porous structure with the pore size matching with the depletion width was fabricated and successfully in-filled by PbS QDs. The porous device produces 5.7% power conversion efficiency, among one of the highest in literature. The enhancement comes from increased light absorption and suppression of charge recombination.

The solid-state dye sensitized solar cell (SDSC) is an emerging photovoltaic technology which promises inexpensive materials, roll-to-roll processing, and a stable architecture. In this thesis, I seek to enhance electronic transport in order to enable thicker devices and yield higher power conversion efficiencies. I adopt a multipronged approach to advance three aims, employing analytical, computational, and experimental methodologies. First, I generalize existing models of the dye sensitized solar cell (DSSC) to allow simple parameter fitting of real devices and to account for previously ignored electronic processes. In Chapter 3 and Chapter 4 I present a nondimensional model capable of fitting real devices and simulating transient behavior without extensive material knowledge. Subsequently in Chapter 5, I introduce a novel three-dimensional model which incorporates electronic drift. Second, in Chapter 4 I critically assess a widespread method of measuring the charge collection efficiency, the summary metric that describes the efficacy of charge transport in the SDSC. I discover that the conventional method is inaccurate for values of the collection efficiency below 90% because of large experimental error and an intrinsic inaccuracy in applying a transient method to measure a steady-state parameter. Third, I aim to increase the rate of charge transport by employing new materials and nanostructures in the place of conventional nanocrystalline TiO2. In Chapter 5, I present evidence of faster transport and enhanced efficiency in flexible SnO2 nanowire SDSCs, ZnO nanowire SDSCs, and the first viable SnO2/P3HT SDSC, where photoanode and hole transporter have been replaced with higher mobility materials. Finally, in Chapter 6, I investigate use of TiO2 mesoporous single crystals (MSCs) with high surface area and extended crystallinity. After demonstrating the viability of MSCs in SDSCs, I examine enhanced transport caused by the background doping effect of thermal treatment. Together, the progress achieved toward diverse and ambitious goals advances the field and delineates routes to future progress for SDSC development.

Dust accumulation on photovoltaic (PV) modules and its effect on their performance are of high concern for regions with a high rate of dust, low frequency and intensity of rain. In this thesis, the effect of dust on PV modules is investigated with respect to dust concentration and spectral transmittance. The measured spectral transmittance of the dust sample shows spectral attenuation effect that varies at different wavelengths. This effect is explained by the particle size distribution of the dust samples: At shorter wavelengths more light is scattered due to the effect of the smaller particles. This effect has a major impact on the PV module as it affects PV technologies with a wider band-gap more than those of a narrower band-gap. The effect of dust is accumulative, i.e. PV module performance is reduced by increasing deposition over time or until it's cleared manually or by rain. The tilt angle of the PV installation plays a major role in the amount of dust accumulated on the devices, where higher tilt angles result in decreased dust concentrations. This effect is demonstrated in outdoor measurements where tilted modules had lower losses in daily as well as total array yield. It is also shown that tilted modules benefit from precipitation more than horizontal modules. However over the exposure period the modules did not show any clear aging effect caused specifically from dust accumulation or exhibit any seasonal variation. Different tilt angles can produce varying non-uniform dust patterns on the device surface. This effect and its pattern over long and short periods of exposure are investigated by means of spatial three dimensional modelling. The simulations compare two dust accumulation patterns that represent a short exposure to a single dusty day (one day) and a long exposure of dust (3 months). Out of the two patterns, the long exposure patterns showed higher losses of 19.4% in comparison to 14.8% for the short exposure. The simulation also showed that dust accumulation that promotes high concentration of dust at the bottom of the PV modules where it covers a full cell has a high risk of triggering hot spots and thus risks permanent module damage. A dust correction model for energy prediction is developed. The model takes into consideration dust concentration, spectral attenuation effect of dust, PV technology, and various meteorological variables. The modified spectral transmittances of the dust were incorporated into the model in the form of pre-measured data. This means in this work samples collected in Kuwait were measured and used to generate the input. The model is compared against the outdoor measured data and a good agreement between measurements iv and simulations is demonstrated. Using this model two procedures were developed. The first evaluates the uncertainties associated with dust over long periods of time. The second is to find the optimised cleaning schedule and frequency of cleaning based on acceptable yield loss margins over the simulated period of time. The optimisation of the cleaning schedule showed that for Kuwait setting the daily energy losses in PV modules at less than 10% will set the cost of cleaning higher than the cost of energy lost due to dust.

The ability for domestic consumers to provide demand response to dynamic electricity pricing will become increasingly valuable for integrating the high penetrations of renewables that are expected to be connected to electricity networks in the future. The aim of this thesis is to investigate whether domestic consumers will be willing and able to provide demand response in such low-carbon futures. A broad approach is presented in this thesis, with research contributions on subjects including data privacy, behavioural economics, and battery modelling. The principle argument of the thesis is that studying the behaviour of consumers with grid-connected photovoltaic ('PV') systems can provide insight into how consumers might respond to dynamic pricing in future low-carbon power systems, as both experience irregular electricity prices that are correlated with intermittent renewable generation. Through a combination of statistical and qualitative methods, this thesis investigates the demand response behaviour of consumers with PV systems in the UK. The results demonstrate that these consumers exhibit demand response behaviour by increasing demand during the day and decreasing demand during the evening. Furthermore, this effect is more pronounced on days with higher irradiance. The results are novel in three ways. First, they provide quantified evidence that suggests that domestic consumers with PV systems engage in demand response behaviour. Second, they provide evidence of domestic consumers responding to irregular electricity prices that are correlated with intermittent renewable generation, thereby addressing the aim of this thesis, and supporting the assumption that consumers can be expected to respond to dynamic pricing in future markets with high penetrations of renewables. Third, they provide evidence of domestic consumers responding to dynamic pricing that is similar to real-time pricing, while prior evidence of this is rare and confined to the USA.

Due to their unique properties, nanoparticles have been a focus of significant research interest for use in various opto-electronic applications, particularly in the field of solar energy generation. In order to realize a nanoparticle-based solar cell, it is important to be able to create thin films of organised nanoparticles and to be able to control their surface properties. In this work the use of a novel synthesis technique involving reaction at the interface between two immiscible liquids to synthesise thin films of lead sulfide nanoparticles on the order of ~10 nm in diameter is reported. The use of the liquid-liquid interface allows the synthesis of particles without the use of stabilising ligands, with sizes and morphologies determined by the conditions present at the interface. Variations in the precursor used, solvent height, and precursor concentration were explored. Films synthesised at various solvent heights displayed a decrease in particle size with increasing solvent height. This trend was seen to vary depending on the lead-containing precursor used. Changes in the precursor concentration resulted in changes in the morphology of the resulting particles as observed with transmission electron microscopy (TEM). Preferential growth along certain planes was observed for particles synthesised with the highest lead precursor concentration. Experiments with precursors with differing organic chain length displayed an increase in particle size with increasing chain length, as well as an increase in preferential growth observed by X-ray diffraction (XRD). Surface ageing was investigated using X-ray photoelectron spectroscopy (XPS) techniques, which showed that all samples followed a similar oxidation mechanism. Oxidised lead species, attributed to hydrated lead oxide, were determined to be the initial oxidation product, formed within a week of exposure to air. Sulfoxy species were observed to form over a greater length of time, with sulfate being determined to be the final oxidation product. An oxidation mechanism is proposed based on XPS analysis of films exposed to air for up to nine months.

Solid-state dye-sensitized solar cells (ssDSCs) offer the possibility of high power conversion efficiencies (PCEs) of over 20%. However, after more than a decade of research, devices still barely reach over 7% PCEs. In this thesis, limitations to device performance are studied in detail, and solutions for future advancement are put forward. In the first part of the thesis, factors limiting charge generation are explored by studying the crystallization environment of mesoporous TiO2 self-assembled through block copolymers. It was found that the density and distribution of sub band gap states are a function of the synthesis conditions and critically affect the performance characteristics of the self-assembled titania used in ssDSCs. As a result, the self-assembled mesoporous oxide system presented in this thesis outperforms for the first time the conventional nanoparticle based electrodes fabricated and tested under the same conditions, with demonstrated PCEs of over 5%. In chapters 6, 7, and 8, the factors limiting the diffusion length and hence, the thickness of the fabricated devices, are carefully examined. Previous literature points towards insufficient pore-filling of the hole transporting material (HTM) as the main limiting factor. In chapter 6, a pore-filling study is shown where a new technique to evaluate the pore-filling fraction of the HTM in the conventional mesoporous metal oxide electrode is also presented and conclude that sufficient pore-filling of thick films can easily be achieved. Another usual strategy to extend the electron lifetime in the devices and thus, the charge diffusion length, involving thin film coatings of insulating metal oxides is examined in chapter 7, with satisfactory results for SnO2-based ssDSCs. The diffusion length can also be extended if the factors limiting the diffusion of charges through the device are identified and removed, as presented in chapter 8. Finally, a study on the stability of the ssDSC is presented in chapter 9. The developments achieved enable long term stability to be effectively targeted, and represent a key milestone towards commercial realization of ssDSCs.

This thesis presents a new type of solar simulator and new measurement methods that allow for fast power rating of photovoltaic devices and for fast performance measurements for energy rating and energy yield predictions indoors under controlled, and more realistically simulated outdoor conditions. A novel indoor measurement system for photovoltaic device characterisation based on light emitting diodes (LEDs) as the light sources is described. The solar simulator is capable of reproducing spectral changes seen in natural sunlight, with its intricacies of variable air mass and weather conditions, to a better match than previously possible. Furthermore, it allows measurements under varying light intensity and device temperature. The prototype LED-based solar simulator developed is characterised and its measurement quality is analysed. The system achieves a class BAA solar simulator classification with a class B spectral match, class A light intensity uniformity and a class A temporal stability. It is the first system of its kind that meets the standards of a solar simulator in spectral match to the standard sunlight spectrum and in terms of minimum light intensity. An uncertainty analysis shows that calibration uncertainty for crystalline silicon solar cells is 5% in maximum power with a 95.45% level of confidence. Recommendations for further versions of the solar simulator are given and show potential of reducing this uncertainty down to 2.9% across all measurement spectra (1.8% with a primary calibrated reference cell). A new method for automated power-rating of single- and multi-junction devices is developed. The method uses a unique spectral response measurement and fitting method. It eliminates the need of external measurement equipment for determining spectral response. A simulated characterisation of an amorphous silicon single- and double-junction solar cell show accuracy of better than 0.5% in maximum power. First measurements on the LED-based solar simulator show a measurement error of 4.5% in maximum power, which is due to a lack of measurement feedback of spectral output and measurement irradiance. The first three-dimensional performance matrix for use in photovoltaic energy rating is reported, utilising the LED-based solar simulator. Device characteristics are measured indoors under varying irradiance, temperature and spectrum. A measurement method is detailed and utilised on a crystalline and amorphous silicon solar cell. It allows for the first time a direct investigation of spectral effects on photovoltaic devices under controlled conditions. Results show that amorphous silicon devices are very sensitive to changes in spectrum. Thus, spectral effects should not be neglected in energy yield predictions for such devices.

The study of photovoltaic materials is important so as to develop new solar energy technologies: in particular, quantum-confined semiconductors could offer increased quantum efficiencies at a much lower manufacture cost. This thesis contains results from a number of pump-probe experiments designed to probe the carrier dynamics in bulk and quantum-confined photovoltaics. A THz time-domain spectrometer was designed, built and commissioned. The THz refractive indices and absorption coefficients of toluene and hexane were determined, and the spectrometer was benchmarked using a photoexcited GaAs wafer. Results are presented of time-resolved THz spectroscopy of photoexcited bulk InP as a function of laser excitation wavelength. These data were used to extract the quantum efficiency of bulk InP in order to compare with recent results for InP quantum dots. The quantum efficiency in quantum dots increases when the incident photon energy is at least twice the band gap energy, whereasthe efficiency of the bulk material is found to decrease. This is because of surface recombination, and these measurements therefore verify the potential superiority of quantum dot materials over bulk materials for use in solar energy applications. Initial measurements of quantum dots using THz spectroscopy highlighted the various experimental challenges involved and the upgrades required to study such samples in the future.The time-dependence of the photoinduced surface photovoltage (SPV) in Si was studied on nanosecond timescales by synchronizing an ultrafast laser system to a synchrotron radiation source (the SRS at Daresbury, UK), and measuring the resulting shift in the photoelectron spectrum. The equilibrium band bending was determined, and the decay of the SPV was attributed to the recombination of charge carriers across the band gap. Results are presented for the SPV in bulk ZnO and for PbS quantum dot chemically attached to ZnO. The fact that the PbS quantum dots were chemically attached to the surface without becoming oxidized was verified using X-ray photoelectron spectroscopy (XPS). The changes caused by photoexcitation occur on much longer timescales in ZnO than Si (sub-milliseconds rather than nanoseconds), and these timescales were conveniently accessed using the time-resolved XPS facility at the TEMPO beamline at Synchrotron SOLEIL (Paris, France). This is due to oxygen adsorption and desorption processes at the ZnO surface affectingthe transfer of charge carriers. The addition of PbS quantum dots to the ZnO surface was found to increase the speed of this charge transfer due to injection of carriers directly from the PbS quantum dot to the bulk ZnO conduction band.

The aim of this work is to research the issue of optimal sizing and location of photovoltaic distributed generation (PVDG) units on radial distribution feeders, and develop new procedures by which the optimal location may be determined. The procedures consider the concept that the PVDG production varies independently from changes in feeder load demand. Based on that, the developed procedures deal with two performance curves; the feeder daily load curve driven by the consumer load demand, and the PVDG daily production curve driven by the solar irradiance. Due to the mismatch in the profile of these two curves the PVDG unit might end up producing only part of its capacity at the time the feeder meets its peak load demand. An actual example of that is the summer peak load demand in Abu Dhabi city that occurs at 5:30 pm, which is 5 hours after the time the PV array yields its peak. Consequently, solving the optimization problem for maximum line power loss reduction (∆PPL) is deemed inappropriate for the connection of PVDG units. Accordingly, the procedures have been designed to solve for maximum line energy loss reduction (∆EL). A suitable concept has been developed to rate the ∆EL at one time interval over the day, namely feasible optimization interval (FOI). The concept has been put into effect by rating the ∆EL in terms of line power loss reduction at the FOI (ΔPLFOI). This application is deemed very helpful in running the calculations with no need to repeat the energy-based calculations on hourly basis intervals or even shorter. The procedures developed as part of this work have been applied on actual feeders at the 11kV level of Abu Dhabi distribution network. Two main scenarios have been considered relating to the avoidance and allowance of reverse power flow (RPF). In this course, several applications employing both single and multiple PVDG units have been solved and validated. The optimization procedures are solved iteratively. Hence, effective sub-procedures to help determine the appropriate number of feasible iterative steps have been developed and incorporated successfully. Additionally, the optimization procedures have been designed to deal with a 3-phase feeder under an unbalanced load condition. The line impedances along the feeder are modeled in terms of a phase impedance matrix. At the same time, the modeling of feeder load curves along with the power flow calculations and the resulting losses in the lines are carried out by phase. The resulting benefits from each application have been evaluated and compared in terms of line power loss reduction at the FOI (∆PLFOI) along with voltage and current flow profile.

This thesis presents the development of innovative tools to investigate spatially distributed properties of thin film photovoltaic devices. They are required to gain a better understanding of device behaviour driven by how such properties affect the performance of commercial-scale devices. The tools developed for this are a distributed 3D model (D3DM) as simulation software and a laser beam induced current (LBIC) system as a platform for characterisation. The D3DM was developed utilising standard circuit analysis software. It is constructed to simulate realistic device structures and current flows in thin film PV devices. Diode parameters are truly distributed and can be varied independently. The model includes a voltage dependent photocurrent which is a key characteristic of amorphous silicon based solar cells. The D3DM has been used for the investigation of spatial variation in performance due to the distributed nature and non-uniformity of diode parameters and solar cell properties. It is shown that distributed series resistance contributed from the contact layers has a significant impact on solar cell performance and efficiency. The LBIC system is an optical scanning based characterisation tool. Unlike most existing systems, this has been developed specifically for large area, module-size thin film applications. The system provides a detailed photocurrent map which reveals spatial non-uniformity and allows investigation of localised performance variation of the investigated PV devices. System development, components and their characterisation as well as different measurement techniques are described. The model is also applied to LBIC measurements where it is used for a sensitivity analysis of measurement signal with respect to certain cell parameters in cells and modules under different measurement conditions. A new limiting illuminated LBIC (li-LBIC) measurement technique was developed. It is a measurement where the laser-probed cell is brought into limiting condition by means of shading. The signal thus generated is a linear response which was previously unobtainable by typical LBIC measurements. It is unaffected by non-uniform illumination allowing the real properties of investigated cells in a monolithic series connected module to be measured non-destructively.

A MicroGrid is typically a small power system, which consists of several microsources and energy storage units, providing heat and electricity to local loads. The MicroGrid has the capability to island and operate autonomously from the main utility network. MicroGrids potentially enable a greater integration of small-scale renewable energy sources. The objective of this thesis is to develop a single-phase microsource interface with energy storage unit embedded into the interface. An integrated energy storage unit avoids the necessity of a separate stand-alone energy storage unit in the MicroGrid. Thus the 'plug-and-play' functionality of the MicroGrid can be improved. A collection of power electronic converter based microsources with storage units connected to form a MicroGrid is a complex system. Development of such simple controllers, which decouple the effect of sub-unit while achieving the desired 'plug-and-play' capabilities, is a complex but important challenge. A photovoltaic panel was considered as the microsource and a battery bank was used as the energy storage unit. The proposed microsource interface consists of three power electronic converters. A photovoltaic panel is connected to a unidirectional dc-dc converter and its output is connected to the input of the single-phase inverter which can be connected to the MicroGrid. Energy storage is connected to the dc-link,which is the input of the single-phase inverter, through a bi-directional dc-dc converter. A simulation model of a photovoltaic panel was developed in the EMTDC/PSCAD software. The limitations of the model and a method to reduce these limitations are discussed. For the experimental validation of the proposed system, an adjustable-voltage-regulator hardware photovoltaic emulator was designed. The characteristic curves of the hardware emulator are compared with those obtained from the simulation model. A controller was designed for the unidirectional dc-dc converter to keep the output voltage of the photovoltaic panel at a given reference. Similarly the controller of the bi-directional dc-dc converter was designed to keep the dc-link voltage approximately constant. The behaviour of the dc-dc converters, which are connected to microsource and energy storage unit, around the steady state and worst-case scenarios was analysed, simulated and experimentally validated. Simulation and experimental results are compared. A current controller, based on instantaneous measured current, was implemented. This was designed to achieve good dynamic stiffness and command tracking properties. Furthermore a smooth grid connection method with the aid of the current controller is presented. The ability of the inverter to control the active and reactive power output was also analysed and verified with the aid of the simulation model and experimental set-up. Results corresponding to current controller, grid connection and power control are presented. The integrated system was simulated in EMTDC/PSCAD. The system response to the variations in the microsource and inverter output power variations was analysed. A smooth start-up method is shown which reduces the inrush current. Simulation results corresponding to different case studies and start-up transient are also included.

Solar Energy and Hydrogen (energy carrier) are possible replacement options for fossil fuel and its associated problems of availability and high prices which are devastating small, developing, oil-importing economies. But a major drawback to the full implementation of solar energy, in particular photovoltaic (PV), is the lowering of conversion efficiency of PV cells due to elevated cell temperatures while in operation. Also, hydrogen as an energy carrier must be produced in gaseous or liquid form before it can be used as fuel; but its‟ present major conversion process produces an abundance of carbon dioxide which is harming the environment through global warming. In search of resolutions to these issues, this research investigated the application of Thermal Management to Photovoltaic (PV) modules in an attempt to reverse the effects of elevated cell temperature. The investigation also examined the effects of coupling the thermally managed PV modules to a proton exchange membrane (PEM) Hydrogen Generator for the production of hydrogen gas in an environmentally friendly and renewable way. The research took place in Kingston, Jamaica. The thermal management involved the application of two cooling systems which are Gravity-Fed Cooling (GFC) and Solar-Powered Adsorption Cooling (SPAC) systems. In both systems Mathematical Models were developed as predictive tools for critical aspects of the systems. The models were validated by the results of experiments. The results of the investigation showed that both cooling systems stopped the cells temperatures from rising, reversed the negative effects on conversion efficiency, and increased the power output of the module by as much as 39%. The results also showed that the thermally managed PV module when coupled to the hydrogen generator impacted positively with an appreciably increase of up to 32% in hydrogen gas production. The results of this work can be applied to the equatorial belt but also to other regions with suitable solar irradiation. The research has contributed to the wider community by the development of practical, environmentally friendly, cost effective Thermal Management Systems that guarantee improvement in photovoltaic power output, by introducing a novel way to use renewable energy that has potential to be used by individual household and/or as cottage industry, and by the development of Mathematical Tools to aid in photovoltaic power systems designs.

A unique measurement system is designed and installed to investigate the performance of high-efficiency PV systems in a high latitude maritime climate. Continuous monitoring of DC and AC currents and voltages of several inverters connected to modules of the latest generation of high-efficiency PV technologies is combined with full I-V characteristics of each module alongside high-resolution meteorological data.

In this dissertation, three major contributions are presented in a photovoltaic (PV) energy system. Firstly, a three-port grid-forming (GFM) microinverter and a lithium-ion battery pack are integrated at the back of PV panel. As a result, they form an AC-PV energy system module that produces an AC output voltage. The technoeconomic analysis, battery capacity optimization, PV panel size optimization, electrical and thermal model of batteries, battery heat generation model, battery management system and thermal management system are discussed in the AC-PV module by using stochastic analysis and battery test results. Secondly, a three-phase 540 KVA bidirectional inverter and a 1.86 MWh lithium-ion battery energy storage system (BESS) were integrated at the Florida Solar Energy Center (FSEC). A case study is performed for this system by acquiring the energy consumption of the building, the reduced energy consumption, the battery testing, the load shifting, and the peak shaving. The total harmonic distortion (THD) values are also provided. Among eight power management scenarios, the scenarios that include PV panels are satisfied via simulation. However, the scenarios that do not include PV panels are analyzed and presented based on the real-world setting measurements. Thirdly, a modified droop control method is designed for grid-tied and off-grid scenarios. The simulation results are obtained based on three scenarios. The first one is that the voltage and frequency regulation control algorithm is discussed when GFM inverters have the equal power ratings. Then, the load sharing control algorithm is determined based on different GFM inverters' power ratings. The last scenario includes Grid connection. Loads are added and removed from the system to ensure that the frequency and voltage stability is the range of continuous operation. The coupling reactance effect on power sharing is investigated.

Abstract: Regardless of the power level, many recent power systems are designed with modular and distributed units forming complex systems. Such large-scale systems normally consist of several units with similar hardware and control configurations, which can be connected to the rest of the system at a Point of Common Coupling (PCC). The higher number of units improves reliability, system efficiency, and energy harvesting, however, it makes the system response analysis and control system design challenging. Interactions between a large number of units and the rest of the system connected to the PCC can lead to unpredictable system behaviors such as oscillations, instability, and undesirable transient responses, which can limit the flexibility and scaling of the system. Therefore, power system studies such as power planning, steady-state, and stability analyses should be continuously conducted to ensure a desirable system performance, which requires an accurate and computationally efficient model for modular large-scale systems. This thesis proposes Weighted Dynamic aggregation (WD agg) approach to model large-scale modular systems with an equivalent unit that has a similar order and structure to an individual unit of the large-scale system. For example, the WD agg model of a PV farm becomes an equivalent single PV array, single inverter, and a controller with weighted average parameters, which hugely reduces the computational burden of the system studies. The parameter weights of each unit are obtained based on the contribution of that unit in the overall dynamic behavior of the system. The proposed approach is applied to find the WD agg model of n parallel DC-DC buck converter to facilitate the sensitivity analyses and control design of the system. Moreover, an equivalent inverter and a controller is found for n grid-forming inverters in an islanded microgrid with droop control power sharing by the proposed WD agg method. Furthermore, the proposed approach is applied to find the WD agg model of n grid-following inverters in large-scale PV farms considering non-linearity of the PV sources. Additionally, the proposed WD agg approach is used to aggregate n induction machine-based Wind Turbine Generators (WTGs) in a large-scale wind farm considering the mechanical and electric machine dynamics. The performance of the proposed method is evaluated by simulations and experiments of small and large-scale DC microgrids, grid-forming inverter-based islanded microgrids, PV farms, and induction machine-based wind farms with equal or unequal parameters with various inputs and stability conditions under harsh power system events such as line-to-line faults and voltage sags for a comprehensive study. The simulation and experiment results show that compared with the existing full-order models, simplified models, equivalent circuits, and conventional full, semi, and cluster/zone agg models, the proposed WD agg model can provide an accurate and computationally efficient single equivalent unit for a large number of units with different operating points and parameters, which can be readily used in the steady-state, transient, and stability analyses with superior accuracy. It also can be used to design the large-scale system controller and unit parameters to ensure a desirable system performance.

Lateral photovoltaic effect has been utilised as an important method for position-sensing applications, including angular displacement monitoring, structural health monitoring and self-power sensors. When a non-uniform light source shines on a semiconductor junction, electron-hole pairs are excited and separated by the built-in voltage across the junction, and a lateral photovoltage is generated between the illuminated and dark areas. To enhance the lateral photovoltage and improve the position-sensing capability, many materials and techniques have been explored to form high-quality heterojunctions. Silicon carbide (SiC) is an excellent material that has attracted a great deal of attention from researchers and industry owing to its superior mechanical, electrical, and thermal properties, and chemical inertness. Notably, among different polytypes, cubic silicon carbide (3C-SiC) has the greatest potential for developing commercial devices because it can be grown directly on the widely available silicon wafers at a low cost. This research investigated the lateral photovoltaic effect in 3C-SiC/Si heterojunctions and explored its potential for developing optical sensors. First, the lateral photovoltaic effect was investigated in an n-3C-SiC/p-Si heterojunction, and its potential for position-sensing applications was examined. In addition, different electrode configurations, such as different electrode sizes and spacings, were evaluated to optimise the design for large lateral photovoltage and highly sensitive sensors. The influence of the SiC layer thickness on the lateral photovoltaic effect was also examined. Next, the behaviour of the lateral photovoltaic effect under external voltage bias was explored. Finally, a freestanding serpentine SiC beam structure was proposed to significantly enhance the lateral photovoltage. The results of this study indicate that 3C-SiC/Si heterojunctions can generate large lateral photovoltage, enabling ultra-sensitive and self-power optical sensors for applications in harsh environments.

The use of renewable and sustainable energy sources such as solar cells have been increasing slowly and gradually. With the rapid increase and growth of solar photovoltaics (PV) production, approximately 22% from 2010 to 2020, high number of PV cells are being manufactured annually. Solar cells have been proven to be an efficient source of renewable energy because of their availability, installation, and affordability. Among all the different types of solar cells, thin-film PV has several advantages over other technologies because of its need for relatively fewer resources, ability to fully automate fabrication process, and the option to fabricate on a more affordable substrate. Nevertheless, the manufacturing process of these thin-film solar cells still involves several critical steps. For example, they still rely on conventional method of laser scribing techniques which in addition to being time consuming, has several reliability issues as well.In this project, the theory of threshold switching method is experimentally verified on Cadmium Telluride (CdTe) PV. The study was conducted by applying different voltage bias configurations to the sample. A drastic decrease in the resistance was observed. The time lapse study of decreased resistance was conducted, which proved that the resistance change is indeed a permanent phenomenon. Our experimental results of threshold switching indicates that this could potentially lead to a scribe-less technology in manufacturing of solar cells which may potentially lead to an increase in manufacturing reliability and efficiency.

Singlet fission (SF), in which two triplet excitons are generated from one photon, has the potential to increase the power conversion efficiency of solar cells. While electronic transitions in the SF process have been studied extensively over the past decade through pump-probe experiments, the role of vibrational coupling remains unclear. Time-resolved absorption and emission bands are typically overlapped and result in ambiguous assignments. Femtosecond stimulated Raman spectroscopy (FSRS) is an ultrafast nonlinear optical technique that investigates vibrational structures of molecules providing both high temporal resolution (∼ 100 femtosecond) and reasonable spectral resolution (10 cm1). In this three–pulse technique, excited and ground state vibrational spectra are obtained to gain structural information about singlet and triplet kinetics in a fast SF process. The evolution of the vibrational spectra obtained during the SF process dictate nuclear coordinate changes and provides key structural information on the reaction mechanism. Here, we investigate the excited-state dynamics of two model SF systems. The first is 6,13-Bis (triisopropylsilylethynyl) pentacene (TIPS-pentacene) in concentrated solution to determine the role of excimer and aggregate formation in SF solutions. The second is a study of intramolecular fission in TIPS-tetracene polymer chain comprised of SF chromophores. Using transient absorption experiments, we unravel the complex photophysics of these systems. Our research extends to tracking vibrations during the SF process using FSRS. We present the time-resolved vibrational analysis of both SF systems. The molecular structural evolution is probed by monitoring vibrational changes in Raman transitions after a variable time delay. The data are compared with density functional theory (DFT) computational results to identify the excited state vibrational species. These results are used to gain further insights to understand the vibrational mechanism of SF in concentrated aggregates and dilute solutions.

Three materials were investigated using two variations of atomic force microscopy and other characterisation techniques. CZTSSe is an earth abundant, non-toxic, semiconductor. Na is often doped into the kesterite structure to improve grain size and overall efficiency. In this thesis Na and other elements are found to migrate in the solar absorber material post deposition. The Na moves preferentially through the grain boundaries, and by applying an external voltage using two capacitor plates, device efficiency is found to be enhanced. The second material investigated is 2D layered perovskite samples BA2Pb(I/Br)4. Using similar external voltage application, nanosized structures form on the surface of the Iodine containing samples. These structures were investigated and found to be highly oriented perovskite structures that enhance crystallinity and conduction attributes. The final material investigated is CGT, a 2D layered magnetic material with a curie temperature of 61K. This material was investigated using a cryogenic MFM system. CGT samples were mechanically buckled forming folds in the 2D sheets. These folds have highly strained areas that were found to show a magnetic contrast at temperatures well above the unstrained curie temperature of 61K. In some samples the enhanced magnetic signal was found even at room temperature, offering future room temperature applicative avenues.

The ascent of perovskite photovoltaics has been one of the most significant and exciting developments in renewable energy research. The myriad of absorber composition blends and compatible device structures offer a wide variety of applications and several paths towards full commercial deployment. However, the rapid decrease in performance of perovskite photovoltaics under operational conditions prohibits their ubiquitous distribution.In this dissertation, a top to bottom approach is utilized to advance the commercial viability of perovskite photovoltaics. Beginning with encapsulation schemes, large-area graphene stacks with a polyisobutylene edge seal were investigated as potential moisture and oxygen barriers for perovskite films. These materials were found to provide a moderate but insufficient protection from a damp heat environment. However, an all-glass encapsulation scheme enabled over 1000 hours of exposure to damp heat (85 ◦C, 65% RH) without any loss in film quality (validated by photoluminescence, UV-Vis spectroscopy, and X-ray diffraction). Attention was then focused on the selective contact layers, beginning with a presentation of electrochemical measurements that were adapted to study the optoelectronic properties, surface coverage, and reactivity of transport layers. Tin oxide, commonly used as an electron transport layer in perovskite photovoltaics, was highlighted as a case study to demonstrate the screening potential of these tools by correlating cyclic voltammetry on a bottom selective contact to final device performance once the device stack was completed. Chronoamperometry was also used to test the reactivity of tin oxide, at the surface, to acidic perovskite precursors, which can potentially be used to predict the reactivity of perovskites at buried interfaces within a device. Next, a solvent-free dry transfer process was designed and highlighted for its ability to deposit a large, uniform film of conjugated polymers which are frequently used as hole transport layers in perovskite photovoltaics. This technique is especially useful for top selective contacts since it eliminates concerns with solvent compatibility of the underlying perovskite film. Lastly, design considerations of the absorber were comprehensiviely explored through the development of a high throughput Perovskite Automated Solar Cell Assembly Line which was used, in combination with active learning principles, to design and test wide bandgap perovskite absorbers for use in silicon-perovskite tandem photovoltaics. Overall, this dissertation presents the steps that we have taken to advances perovskite photovoltaics from an intriguing research project to an effective and vital technology that aid in addressing the ever increasing global energy demands.

As the world continues to move toward clean renewable energy, the need for solar energy onlybecomes more necessary. Photovoltaic devices are comprised of a semiconductor and metal layersthat allow the solar cells to convert light to electrical energy. The composition of the primarysemiconductors used in this research are p-type Cd(Se,Te) with Mg(Zn,O) as a n-type partner anda Perovskite with a Carbon-60 (C60) interface. The efficiency of these photovoltaic devices maydecrease significantly as they are used. The goal of this research is to determine the underlyingcause of Cd(Se,Te) and Perovskite device degradation when exposed to light and heat. Finiteelement device simulations were employed to analyze performance metrics, including efficiency,fill factor, open-circuit voltage, and short-circuit current. Numerous simulated current vs voltagecurves of varying doping and defect levels were used to obtain the various performance metrics.Cd(Se,Te) performance metrics were simulated with various MZO doping, interface defect densityand electron affinities. Perovskite performance metrics were also simulated with various defectdensities at the Perovskite/C60 interface, defect density at the Perovskite/Hole Transport Layerinterface and C60 electron affinity. Results were compared to pre/post stress experimental dataof Cd(Se,Te) and Perovskite photovoltaic devices in attempt to determine the potential cause ofirreversible degradation. Results suggest that a decrease in MZO electron affinity and an increase inMZO/Cd(Se,Te) interface defects during light/heat stress cause the observed degradation. For theperovskite devices, results suggest that the course of degradation was an increase in C60 electronaffinity and increase in defect densities at the Perovskite/C60 interface.

CdTe thin-film solar cells have become popular due to low manufacturing cost, but this benefitcomes at the expense of cell performance. While performance is improving, CdTe is still plagued byopen circuit voltage (VOC ) losses. These losses are attributed to interface and bulk recombination,but with current methods, evaluation of these properties is convoluted. This thesis reports onTRPL simulations on a Cd(Se,Te) double heterostructures (DHs), a semiconductor material thatacts as the absorber layer in commercially relevant thin-film solar cells. TRPL was simulated onAlumina/Cd(Se,Te)/Alumina DHs, where alumina acts as an excellent surface passivation agentfor Cd(Se,Te). Simulations were conducted with COMSOL Multiphysics®, where time-dependentcharge transport equations and Poisson’s equation were numerically solved using the finite elementmethod. Models were created to investigate the effects of bulk, surface recombination, mobility, andmaterial thickness. These models used single photon excitation (1PE) and two-photon excitation(2PE) to examine the surface and bulk of the material. Results were analyzed to develop a combinedexperimental and numerical simulation procedure to distinguish and quantify bulk and interfacerecombination mechanisms in Cd(Se,Te) photovoltaic devices. This general approach can be appliedto other thin film solar cells to help determine where significant VOC losses are occurring.

In the United States, smart PV inverters integrated with residential distribution systems are becoming a more common occurrence. With integration of smart PV inverters, power utilities are experiencing an increase of number of operations with regards to switched capacitor banks, voltage regulators and on load tap changers. These increases can lead to excess wear and tear on the devices causing power utilities to perform unwanted replacement and maintenance. However, smart PV inverters when controlled under specific functions can enable these inverters to provide reactive power and voltage control which in turn lowers the number of operations for switched capacitor banks, voltage regulators and on load tap changers. Furthermore, the standard basis is that when implementing Unbalanced Residential Distribution Systems into the grid, centralized control is a well-known choice, however, decentralized control provides a strong case for usage when using smart PV inverters in residential distribution systems. The objective of this thesis is to provide a better understanding of Unbalanced Residential Distribution Systems tied into the distribution side of the power grid when using control functions. Furthermore, better understand and prove the theory of using decentralize control for smart PV inverters in a residential distribution system. The future work will be analyzing the role of restoration practices and islanded mode with control algorithms that are used in grid connected mode. The specific areas below will be discussed in this thesis

The goal of this work is to increase solar cell efficiency by efficiently combining the electric power of a solar cell and a thermoelectric generator into a single two terminal hybrid device. This work presents a method of achieving this by dividing the thermoelectric generator into smaller thermoelectric generators, forming a parallelly connected network with them, and connecting this network in series with the solar cell. An equivalent circuit model was developed for this device scheme and compared with experimental data. The data show some support of the model, but fine evaluation of the model’s accuracy was hindered by limitations in the experimental setup. If thermoelectric generator efficiency increases in the future, it may become practical to combine thermoelectric generators with solar cells. Providing a method for combining the two power sources at the cellular level may be important for simplifying and improving systems that use these photovoltaic/thermoelectric hybrids.

Rapidly growing consumption of energy derived from carbon-based fossil fuel has caused energy crises, global warming, and air pollution. Therefore, the development of renewable energy is required. Solar energy has been considered as a promising renewable energy source since it is clean, inexhaustible, and abundant in nature. Therefore, many technologies have been studied for harvesting solar energy including photovoltaics, solar heating, concentrating solar power, and solar-driven water splitting. In this dissertation, we demonstrate a variety of approaches for improving solid-state devices for harvesting solar energy via the photovoltaic effect or photoelectrochemical water splitting. First, we demonstrate improved passivation quality for Si photovoltaic devices using i a-Si:H films with a gradient-layered structure consisting of interfacial, transition, and capping layers deposited on c-Si surfaces. The H₂ dilution ratio (R) during deposition was optimized individually for the interfacial and capping layers, which were separated by a transition layer for which R changed gradually between its values for the interfacial and capping layers. This approach yielded a significant reduction in surface carrier recombination, resulting in improvement of the minority carrier lifetime from 1480 μs for mono-layered i a-Si:H passivation to 2550 μs for the gradient-layered passivation approach. We then demonstrate approaches for design and fabrication of Si-based photoelectrochemical devices that demonstrate high performance and stability for solar-driven water splitting. Metal-insulator-semiconductor (MIS) structures are widely used in Si-based solar water splitting photoelectrodes to protect the Si layer from corrosion. Typically, there is a tradeoff between efficiency and stability when optimizing insulator thickness. In this study, we demonstrate improved Si-based MIS photoanodes with thick insulating layers fabricated using thin-film reactions to create localized conduction paths through the insulator and electrodeposition to form metal catalyst islands. These fabrication approaches are low-cost and highly scalable, and yield MIS photoanodes with low onset potential, high saturation current density, and excellent stability. By combining this approach with a p⁺n-Si buried junction, further improved oxygen evolution reaction (OER) performance is achieved with an onset potential of 0.7 V versus reversible hydrogen electrode (RHE) and saturation current density of 32 mA/cm² under simulated AM1.5G illumination. A two-step Ni/NiFe electrodeposition process is then demonstrated to create more efficient OER catalysts. The Ni/NiFe catalyst layers increase Schottky barriers between Si and metal catalyst and lower the photoanode onset potential, improving applied bias photon conversion efficiency (ABPE) to a Ni catalyst, to 3.5%.

Solar Thermoelectric (TE) uses thermoelectric modules to absorb radiative energy given off by the sun and convert it into electricity. While its main competition, photovoltaic panels boast an efficiency of around 20%, solar TE panel can only muster around 5-7 % efficiency. This reason along with high material and manufacturing cost has been the cause as to why solar TE has not been extensively explored as an alternative solar energy harvester so far. However, due to the increasing effects of global warming, alternative sources of harnessing energy such as solar TE have been more closely researched. In the past decades, scientists have synthesized new TE materials that have shown great promise in increasing efficiency and power output, surpassing even the properties of Bismuth Telluride-based alloys, which have been widely used for low-temperature TE applications due to having one of the best efficiencies and power output available in the temperature range.This new materials discovery promises a great new technological innovation for the field of thermoelectric for years to come, but there are not many tools currently available that can simulate the effect of harnessing solar radiation using these materials. The Concentrating Solar Thermoelectric Generator Tool developed in the work takes advantage of the ever-developing world of thermoelectric materials by inputting users’ newly developed or already known thermoelectric properties into the simulation. By using the users’ own data, a power output and efficiency can be presented with varying independent variables: the cross-sectional area and thickness of the TE element, solar concentration, and fractional coverage while also taken into consideration the optical parameters and emissivity of the grey surfaces and heat transfer, amongst other data for an ideal optimization of solar TE design.This tool is intended to bridge the gap between the theoretical and experimental by introducing a way that scientists and researchers can simulate known and theoretical materials. We find that the result adequately depicts power output and efficiency in neat and accurate plots with respect to their independent variable. We describe the methodology for the solar TE design optimization in terms of system efficiency and cost. For the latter, we show that strategically reducing the fractional coverage and thickness of TE elements by similar factors can keep the thermal load matching condition satisfied for system efficiency, while significantly reducing the material cost to ultimately achieve a much-reduced cost per power of $0.07/Watt. The link for the solar TE tool can be found at: https://nanohub.org/tools/solarte

Over the years, it has become apparent that renewable radiation has the highest potential as a form of energy. Since incident photons may produce energy, one of the best renewable power collecting applications is photovoltaic. However, there are still obstacles such as efficiency reduction caused by the heat generated. Another energy saving concern is the severe energy loss of the residential and commercial buildings through window. The SHIELD initiative, which is supported by a department of energy agency in the US, advocates substituting multiple pane windows with single-pane windows for cost- and energy-effectiveness. By depositing PT substances on one side of the glass, we are able to raise the temperature of the panel itself and achieve energy balance on both sides of the glass, a performance innovative solution by our innovation strategy of visible transparent thermal isolation.Photothermal material (PT) should be wavelength tunable with high visible transparency and highly absorptive to ultraviolet and infrared spectrum bands. Iron oxide nanoparticles and iron oxide coated by copper sulfide nanoparticles will be studied in both solid and liquid systems. We will employ single wavelength light and AM 1.5 to investigate the PT characteristics of Fe3O4 with polymer coatings and Fe3O4@Cu2-xS with polymer coatings on the glass substrates. The PT mechanisms will be identified based on the thin coating’s localized surface plasmon resonance (LSPR) effect and Mie theory. Wavelength tunable materials as thin coatings will be designed, synthesized, and deposited on various transparent substrates. Without the use of any extra thermal isolations, such PT coatings will raise the surface temperature of the glass and significantly lower the U of single pane windowpanes. In this way, a wavelength-tunable, transparent PT coating offers a possible option for the Department of Energy's SHIELD program. In our study, PT materials as thin film coatings will be irradiated by different light sources, including AM 1.5 and single wavelength light, for energy saving application. It has been shown that porphyrin complexes have both light-to-electricity (PV) and light-to-heat (PT) capabilities for solar energy sustainability. It is generally recognized that porphyrin chemicals may be used as photosensitizers for dye-sensitized solar cells and perovskite solar cells. On the window surface, wavelength tunable PT coatings on the glass substrate are deposited for isolating heat and light modulation. The PT coating can dramatically increase the surface temperature of the window during solar irradiation, resulting in greatly decreased heat transfer, determined by a low U-value, and filtering unwanted light frequencies for PV panels. The PT-PV double functional devices can be adjusted seasonally according to the energy requirements. Wavelength tunable PT films provide additional effective solar light harvesting; whereas the UV and visible wavelength parts can be employed for PV applications, the infrared can be utilized for heat energy applications. This will allow for further research and development in the field of spectrally tunable sun harvesting and energy generation.

Thermophotovoltaic (TPV) generators have emerged as promising heat engines for use in a wide range of emerging energy generation and storage applications. This approach to energy conversion leverages the photovoltaic effect to convert locally emitted thermal radiation (heat) to electrical power. TPVs are positioned to facilitate the growth of intermittent, renewable energy sources because they can deliver power quickly and efficiently in response to sudden changes in energy demand at various scales. Through integration with thermal batteries, TPVs may enable one of the most affordable and energy-dense approaches for grid-scale electricity storage. TPVs are further well-suited for utilization in distributed co-generation, an alternative to centralized power generation that may reduce energy loss associated with waste heat and electricity transmission. Despite the appeal of TPVs for use in these promising energy generation and storage technologies, TPV conversion efficiencies remain well below their thermodynamic limits. Practical deployment of the technology is therefore predicated on continued advances in performance. The fundamental challenge of thermophotovoltaics pertains to regulation of the radiative heat transfer between the thermal emitter and the photovoltaic cell. Given the moderate temperature of the thermal emitter, only a small fraction (~20%) of power is usable by the photovoltaic cell. The remaining, unusable power must be properly managed to avoid substantial loss. The present work aims to eliminate radiative loss in thermophotovoltaic systems to improve their conversion efficiencies. This thesis begins with an exhaustive review of the TPV literature that features a thermodynamic framework for meaningful comparison of dissimilar works. This review helps to recognize leading materials and design choices and identifies opportunities for continued improvements. Spectral inefficiencies are shown to persist as the largest loss pathway for TPVs. The first of three experimental demonstrations herein involves the realization of thin-film InGaAs optical structures through non-destructive epitaxial techniques. This technique enables recovery and subsequent reuse of the expensive crystalline growth substrate for reduced cell costs. Further, optimized dielectric claddings are shown to improve the spectral performance of the optical structures. Specifically, use of a MgF2 rear spacer enables record-high out-of-band reflectance of 96%, an improvement over cells with conventional metallic rear reflectors. Secondly, this thesis demonstrates a novel cell architecture featuring air pockets buried beneath a InGaAs/InP heterostructure absorber with near-complete (98.5%) reflectance of out-of-band power. This spectral advance enables record-high conversion efficiency of 32% under illumination by a 1455K SiC emitter, representing an 8% efficiency improvement over a control cell. Lastly, this thesis describes the development of an entirely new approach to spectral management based on partially transparent cells. Optical analysis of a proof-of-concept optical structure decouples radiative loss in the heterostructure absorber and the supporting substrate to show a pathway to a new regime featuring

As solar PV deployment increases in the U.S., so will the volume of decommissioned PV modules and balance of system equipment, and large amounts of annual waste are anticipated by the early 2030s. Currently, there are over 65 GW of solar PV installed in the U.S., which is the equivalent of over 5 million tons of PV modules. In order to get ahead of this looming, as well as present challenge, our team has worked with the National Renewable Energy Laboratory (NREL) to conduct an in-depth study of material flow pathways from PV system decommissioning to secondary use applications and recycling in order to inform an evidencebased assessment of decommissioning trends and regulatory policy in the United States. Our study focused on four main themes: (1) an analysis of U.S. decommissioning policies and regulations, (2) an analysis of U.S. decommissioning costs, plans, and trends, (3) a comparative analysis of international decommissioning policies and regulations, and (4) a market analysis of the potential for a U.S. PV system circular economy. Decommissioning costs are still poorly understood but are expected to be a not trivial part of the total lifetime cost of solar PV systems. Our analysis of 24 decommissioning plans from 9 different states showed considerable variation in estimation methods and outcomes. The costs reported ranged from -$226,000/MW (for a project for which the value of salvage materials was expected to exceed costs) to $105,000/MW with an average of $9,525/MW. We concluded that it was not possible to do any further analysis or comparison across the entire set of plans, given the vastly different methodologies utilized. To support additional insights, we thoroughly reviewed each plan and separated the methods into three categories: Per unit; single number lump sum, and itemized lump sum. We then drew on our extensive knowledge of the plans to develop a set of confidence criteria that can be used to score a given decommissioning plan’s methodology. Transparency of methods and assumptions, strength of the estimator’s credentials, and inclusion of comprehensive set of components were the most important factors influencing our confidence in each plan. We ultimately found that our confidence was on average highest for plans using a per unit method, followed by plans using an itemized lump sum method. We had the least confidence in plans using a single number lump sum method. While we were able to develop qualitative metrics for confidence, it should be noted that it was impossible for us to judge the empirical accuracy of any particular method. This is because no reliable data on actual decommissioning cost currently exists. We concluded that filling this data gap as well as establishing a more standardized approach for estimating decommissioning costs would benefit both local planners and solar developers. Secondary markets and services for new, used, and end-of-life PV modules are becoming increasingly important to managing material flows and establishing a circular economy for PV modules. In the context of PV modules, secondary markets are the markets that facilitate transactions between buyers and sellers for goods that have already been sold into the primary market by a manufacturer, distributor, retailer, etc. Secondary markets are particularly useful for keeping PV modules in use that would otherwise be landfilled or recycled and for providing backup supply when primary markets face increased demand. As PV material flows out of secondary markets increase, it is imperative that those materials are managed responsibly under a circular economy system. Creating a U.S. PV system circular economy is in part dependent on the availability and affordability of solar PV module recycling services and economic value that module owners can recoup from selling PV modules to recycler or selling recycled module materials into recycled and commodity materials markets. Secondary market outlets and PV module recycling services and materials markets are showing promising growth and traction, but will continue to face headwinds from improvements in PV technology performance, declining PV prices, government incentives for new systems, and consumer and regulatory skepticism towards used systems. In the absence of solar PV-specific waste laws in the U.S., and regulations mandating the collection and recycling of solar PVs at the end their useful lives, U.S. states and their local jurisdictions are beginning to develop their own processes of regulating the responsible management of solar PVs.1 As solar PV deployment increases in the U.S., so will the volume of decommissioning solar PVs within communities. Solar ordinances and decommissioning policies are becoming increasingly important considerations within U.S. State and local jurisdiction’s planning practices. Currently, there is little information about what purpose the policies are intended to serve from the local perspective. However, because such policies may have implications on the development of solar projects across the U.S., it is important to understand why U.S. states and localities passed solar decommissioning policies in the first place, what stakeholders are or should be involved in the development of such ordinances, and what impacts solar policies are having on the solar industry. By reviewing U.S. state and local regulatory frameworks and ordinances, the project team sought out to better understand how local communities are responding to increased renewable energy project developments and identify potential impacts state and local decommissioning policies may have on various stakeholders including developers, state and local authorities, landowners, and community members. Many international jurisdictions are wrestling with how to responsibly manage material flows of decommissioned and waste PV modules and energy storage technologies. Certain member countries of the European Union have robust materials management frameworks in place, and continue to refine regulations that govern these waste types. Other countries, such as Australia, China, and Japan, are taking steps to develop their own regulatory frameworks. While government officials are responsible for enacting and enforcing regulations governing solar and storage wastes, in virtually every jurisdiction we studied solar industry stakeholders played an important role in shaping solar and storage waste management policies. The importance of industry input on how waste management policies are crafted and contribution to developing the technologies, business models, and operational capabilities needed to manage secondary markets and waste material flows cannot be overstated. The research and analysis performed in this project is essential to the understanding and formation of a sustainable circular economy for solar photovoltaic energy generation. Our greatest desire is that this work informs and inspires many others in this impactful and promising field.

Electrical contact formation is required for the transport of generated current from solar cells. Currently, Ag screen printing is the dominant metallisation method, but it accounts for ~ 60% of the non-wafer mono cell price. Copper, a less expensive material applied with plating has been the envisioned substitute for years; manufacturers, however, are reluctant to make this shift due to reliability and adhesion concerns. This thesis aimed to investigate the importance of contact adhesion for plated metallisation. A finite element model of the stylus-based adhesion measuring process was developed in order to quantify the different contributions due to interfacial adhesion, finger geometry and finger material. It was found that the largest contributor of the measured force was interfacial adhesion, accounting for > 90% of the total measured value. Finger material accounted for only ~5% of the total measured force, with finger geometry having little to no effect on the measured force provided that the area in contact with the Si is kept the same. The simulations also shed light on why different finger breaks (cut-off and dislodgement) are observed during measurements and it was concluded that dislodgement breaks can occur due to low interfacial adhesion, non-uniform adhesion across a surface or plasticity of the finger material. An automated classification of finger break type based on a feature detector and trained via machine leaning was developed for use with the adhesion testing method. The classifier was able to quickly classify fingers breaks (3.2 s for 500 classifications) demonstrating the potential to perform and analyse finger adhesion measurements in production measurements. Weak contact adhesion was shown to impact module durability. Power degradation of up to 15% was observed after 250 hours of damp heat exposure, due to pseudo fill-factor (pFF) loss. Subsequent cross-sectional analyses identified that, due to finger detachment, Cu was able to diffuse into the Si wafer and form precipitates close to the p-n junction. Finger contact adhesion was weakest for modules which used immersion capping layers (Ag and Sn) as these immersion chemistries under etched the Cu fingers resulting in poorer finger adhesion. Finally, this thesis brought together past and present findings to present a comprehensive overview on stylus-based adhesion testing for plated metallisation.