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L’energia solar fotovoltaica és una de les principals fonts renovables d’electricitat gràcies a la gran quantitat de recurs solar de què disposa la terra. Actualment, les tecnologies fotovoltaiques de silici cristal·lí dominen sobre la resta, amb una presència al mercat del 30% per als mòduls fotovoltaics de silici monocristal·lí i 60% per als de silici policristal·lí, però des de fa 30 anys noves generacions de fotovoltaiques han anat sorgint per fer front als principals desavantatges d’aquesta i, alhora, aportar nous atributs per a estendre el seu ús a altres aplicacions. La fotovoltaica orgànica és una tecnologia fotovoltaica de tercera generació particularment prometedora en aplicacions d’integració de mòduls fotovoltaics en elements constructius d’edificis, o BIPV (Building Integrated Photovoltaics), gràcies a les seves propietats de flexibilitat i transparència i el seu econòmic procés productiu mitjançant tècniques contínues de recobriment i impressió d’alt rendiment, baix consum energètic i amb capacitat de produir grans àrees. Amb aquests prospectes, s’han produït uns mòduls fotovoltaics orgànics semitransparents amb una capa activa basada en la heterojunció dels polímers P3HT i PCBM, dos elèctrodes transparents i un cristall fotònic per a maximitzar l’absorció de la irradiació solar. El treball inclou una anàlisi del procés productiu, del comportament elèctric i de la transparència dels mòduls. Alhora, s’efecuta l’extrapolació dels resultats a una futura producció a gran escala per determinar la viabilitat d’aquests mòduls en qüestió de costos, rendibilitat i efectes sobre el medi ambient. Tots aquests aspectes de la fotovoltaica orgànica son comparats amb la fotovoltaica convencional de silici cristal·lí. L'objectiu és que, en un futur no llunyà, la fotovoltaica orgànica pugui competir-hi en quota de mercat mitjançant la seva implantació i fidelització en una part d’aquest, potencialment molt extensa en utilitat i àrea, com són les façanes i altres elements d’edificis, en què els mòduls de silici cristal·lí no tenen cabuda per les seves propietats. Els principals reptes d’aquesta innovadora alternativa a la fotovoltaica convencional de silici cristal·lí són una millora en l’eficiència i, sobretot, en l’estabilitat, ja que la degradació és una gran contraindicació per a la seva integració en edificis.

At present there is an increase of the energy generated by means of renewable energies. One of the main sources of renewable energy is solar energy, which is produced by photovoltaic cells. One of the most recent types of photovoltaic cells is the organic photovoltaic cells (OPVs), which have interesting mechanical characteristics but have a relatively low yield The low performance of the OPVs is their main problem and to improve this performance one has to investigate and deeply understand the mechanism of the operation of these solar cells. In order to achieve this there is a problem that has to be prepared first, the material that compose the cell is amorphous and, therefore, it is difficult to investigate the structure experimentally. Since solving the structure is fundamental to learn how OPVs operate accurately then we will use computational methods per resolve the structure. The system to be studied consists of molecules p-DTS (FBTTh2) 2 and PC71BM. Since the molecules are very large It’s not possible simulate the system using a very precise quantum method because calculations would take too long, therefore we resort to force field methods that are faster but less accurate. In order for the results of the force field methods to be the closest to the results of the quantum methods, we will perform a parameterization. To do this parameterization we will divide the system into different parts: the molecule p-DTS(FBTTh2)2 will be divided into three fragments and the molecule PC71BM will be simplified to C70 fullerene. The parameterization itself will be based on parameterizating the rotation of the dihedral angles between the aromatic rings of the three fragments of the molecule p-DTS (FBTTh2)2, since this is the most flexible part of the fragments. It will also parameterize the stacking in the three fragments. Once the p-DTS(FBTTh2)2 molecule is parameterized, the C70 molecule will be parameterized. Specifically, only the stacking between two molecules of C70 fullerene will be parameterized

Photovoltaic (PV) modules may experience degradation as soon as they are exposed to outdoor weathering conditions. This occurs from the early stages of installation up to the decommissioning stage. PV degradation exists in many forms, some of which occur during the first few months of exposure, while others depend on the materials’ susceptibility to continuous weathering. The Maltese climate is characterised by high levels of solar radiation, humidity and temperatures. These three factors together with coastal region conditions may affect the performance of the PV module during its lifetime. The aim of this research was to gain an understanding of the visual degradation modes together with the rate of loss in maximum power over a number of years of operation. PV modules operating over a range of one to twenty-eight years were analysed. This would provide a clear picture to the installers and investors on the expected degradation in power per year for warranty and energy yield purposes. The results showed that modules with more than eighteen years of operation experienced a greater degradation rate per year in maximum power, when compared to those up to fourteen years operating under Maltese climatic conditions. This implies that the newer modules use improved materials such as UV-stabilised encapsulation, protection against humidity ingress, among others., peer-reviewed

Photovoltaics have developed rapidly over a past decade. In the end of 2013, the total of solar PV global capacity reached 139 GW. The fast development of solar photovoltaic is mainly due to the improvement of solar cell efficiency and the decrease of the costs. The absolute cost of photovoltaic depends on the technology. The photovoltaic market is currently dominated by crystalline silicon. For crystalline silicon photovoltaic, the material cost represents 40% of the total module cost. On the other hand, the emerging technologies of photovoltaic require expensive and scarce materials. Hence, it is necessary to reduce the usage of raw materials in order to decline the cost of solar photovoltaic. One solution to save raw material is reducing the thickness of absorber solar cell. However, reducing the thickness of active layer could compromise the optical absorption. The main focus in this work is to develop nano solar cell integrated within optical nano resonator which is in the main frame of the PhD thesis work of Proise (Study and Realisation of Micro/Nano Photovoltaic Cells and Their Concentration Systems). Proise developed the simulation of the geometry of nano-resonator solar cell in order to optimise the absorber thickness while keeping a good absorption. Based on Proise’s result, the geometry of nanoresonator solar cell with a thickness of 350 nm, a width of 100 nm, and a period of 400 nm is decided to be fabricated. The semiconductor materials used in this work are based on III-V semiconductors, Indium Phosphide (InP) and InGaAs. InGaAs is expected to improve the ohmic contact between metal and InP since it has lower barrier height than InP. However, InGaAs can reduce the optical properties of nano-resonator solar cell since InGaAs can absorb the light. Therefore, the study of the contact resistance between metal and semiconductor and the influence of p-type InGaAs layer inserted between p-type InP and metal layer are performed in this work. The fabrication involves UV lithography and wet chemical etching. On the other hand, the characterization is conducted through transmission line measurement and micro-diode measurement. In this work, it is found that the InGaAs has an influence to reduce the series resistance of solar cell. As an ultimate goal in this work, the fabrication of nano solar cell integrated within optical nano resonator is performed. It involves the design of the mask for electron beam lithography, anodic bonding technique, electronic beam lithography, and dry etching. The results are observed through scanning electron microscopy. In this work, the geometry of nano-resonator solar cell has been developed successfully with a period of 400 nm.

With increasing price of natural gas and petroleum products and their environmental concerns, alternative energy sources are required i.e. renewable energy sources. Solar energy is the abundant form of renewable energy. In addition to that, the total amount of solar power that incident on earth for an hour can cover the world’s annual electric power demand. Hence capturing even fraction of this abundant power source is vital. The technologies used to capture solar power are the photovoltaic systems which, through the photovoltaic effect in semiconductors in the solar cells comprising the system; convert the energy in the photons of the sunlight directly to electric power. The system with silicon solar cells has high production cost because of which it has been difficult for the system to be in to grid parity. The best alternative that attracted the attention of many researchers in the world is to use organic solar cells. Unlike their inorganic counterparts; the organic solar cells are easy and cheap to fabricate, light weighted, flexible, the semiconductors are tuneable with respect to their functions, colourful, can absorb light in cloudy days and semitransparent. The amount of semiconductor material required is very small (i.e. in 100nm). Because of these, even with half efficiency of inorganic ones can make them economical. The other advantage is that they can be used in areas where silicon solar cells haven’t been used and properties like light weightiness, flexibility and colourfulness are required. This could be in the sports, agriculture, medical sector …. However, they have disadvantages: low efficiency and shorter life span due to degradation of the semiconductors. Some of the factors that determine performance of solar cell are the type of structure used for the active layer of the solar cell and its thickness. The two kinds of structures we used in the lab were the bi-layer and bulk-junction photoactive layer. The performance of the bulk-junction solar cells increase with thickness of the photoactive layer up to certain point due to high intimacy of contact between the donor and acceptor and from this point on wards the performance decreases as recombination starts to dominate the effect of the intimacy of contact. Comparison of the bi-layer and bulk-junction solar cells for certain thickness tells that the bi-layer has higher fill factor and open circuit voltage than the bulk-junction due to relatively low recombination and density of states. The efficiency of organic solar cells is increasing at higher rate recently as researches have been taking place even in big named companies. The degradation of the organic semiconductors is due to oxygen and water valour from air which can be avoided by encapsulation of the solar cells.

A novel photolithographic technique which promises quick and easy large area patterning is explored to satisfy the nanowire applications requirements. Nanohole patterns for ordered nanowire growth and nanopillar arrays for PV applications are produced by means of Near Field Phase-Shift Photolithography. Furthermore, solar cells based on silicon nanopillars have been fabricated showing high e ciencies. The quality of di erent passivating materials was evaluated in this particular approach, concluding that a double layer of SiO2/SiNx is the most appropriate. Outgoing

En este trabajo se presenta un estudio mediante espectroscopía Raman de capas CuInSe2 sintetizadas en condiciones de defecto de Cu, en función de su composición. El interés del estudio viene motivado por el potencial de este material como capa absorbedora para células solares de alta eficiencia y bajo coste. En el estado actual de la tecnología, estas capas se sintetizan en condiciones de defecto de Cu para evitar la formación de fases secundarias Cu-Se. En una primera parte, se han analizado las condiciones experimentales idóneas para las medidas Raman, lo que ha implicado un estudio de la presencia de efectos de potencia en los espectros. Se han analizado capas con diferentes relaciones Cu/In. La interpretación de los espectros permite deducir la coexistencia en las capas de fases desordenadas con vacantes (OVC) junto con la fase calcopirita, lo que ha sido corroborado mediante medidas de XRD. Las medidas han permitido fijar el rango de composiciones en que se produce la coexistencia de estas fases. El proyecto cuenta con la colaboración del centro de investigación "ZSW: Zentrum für Sonnenergie und Wasserstoff-Forshung, Baden-Württemberg", en el marco de un proyecto europeo en que participa el Dept. de Electrónica de la Universidad de Barcelona.

In this thesis, the structural, optical and electrical properties of crystalline silicon quantum dots (SiQDs) are examined for application to silicon based tandem cells. The approach has been to concentrate on all silicon devices by taking advantage of quantum confinement in low-dimensional Si. RF magnetron co-sputtering provided the capability of creating superlattice structures in conjunction with high temperature annealing, to form Si nanocrystals in an oxide matrix. Structural techniques, including Fourier transform infrared spectroscopy (FTIR), micro-Raman spectroscopy, transmission electron microscopy (TEM), X-ray diffraction (XRD), and Secondary ion mass spectroscopy (SIM) were employed to gather structural information about the SiQD/SiO2 SLs. The result combine presents that the packing density of Si QDs, correlated to the oxygen content of the silicon rich oxide layer can be control independently. The effect of Si nanocrystallite density on Raman scattering is investigated. The preliminary results present that a decrease in the oxygen content (x) results in an increased sharpness of the Strokes-mode peak of nanocrystalline Si, attributed to an increase in the proportion of crystalline Si because of the increased number of SiQDs. However the influence of the surface region on the crystallite core intensity scattering becomes dominant, when SiQD size diameter is very small (less than 3 nm). The present work shows that a decrease in x-content leading to an increase of the SiQD concentration, initially results in the enhancement of the lateral conductivity in the SiQD superlattice material. In this work, the Al contacting scheme, using a prolonged heat treatment technique at elevated temperature less than the eutectic point of Al and Si (577C) has been successfully applied to making Ohmic contacts on both SiQD SLs in oxide and nitride matrices. Activation energy (Ea) of SiQDs, extracted from a linear Arrhenius plot is investigated in the present work in order to expand the understanding of engineering electrical injection in laterally active paths. It is found that a lower barrier height of dielectric matrix influences to the lateral electron transport of the SiQDs in such dielectric matrix. PL results confirm that the band gap of surface oxidized SiQDs widens due to quantum confinement. The present results reveal that the strong peak (Q-peak) due to quantum confinement is more effective in the emission with increasing SiQD concentration. The surface oxide is believed to play an important role in the reduction of SiQD luminescence due to a trapped exiciton. It is concluded that SiQDs surface oxide accompanied by a SiO2 matrix may not provide a good passivation in very small SiQD size. However the energy band gap and conductivity of the SiQDs are tunablity, in the optimum range of SiQD size and concentration. This observation may be important for future nanoelectronics applications.

This thesis focuses on improving the adhesion of electroless metal layers plated to pit contacts in interdigitated, backside buried contact (IBBC) solar cells. In an electrolessly plated, pit contact IBBC cell, the contact grooves are replaced with lines of pits which are interconnected by the plated metal. It is shown, however, that electroless metal layers, plated by the standard IBBC plating sequence, are not adherent on pit contact IBBC solar cells. The cause of this adhesion problem is investigated by examining the adhesive properties of each of the metal layers in the electroless metallization sequence on planar test structures. This investigation reveals that Pd activation of heavily P diffused Si impedes Ni silicide growth and that, in the absence of a silicide at the Ni/Si interface, an electrolessly plated Cu layer will cause the underlying Ni layer to peel away from the substrate. It is also found that the Ni silicidation process itself intermittently causes the unreacted Ni to spontaneously peel away from the substrate. An electroless metallization sequence that results in thick, adhesive Cu deposits on planar &lt 100&gt surfaces is developed in this thesis. It is shown that this process leads to the formation of a Ni silicide on both n- and p- type, heavily diffused surfaces. Fully plated, pit contact IBBC solar cells were not able to be fabricated during the course of this work but it is reasonable to expect that the modified plating sequence developed in this work will result in the metal layers being adhesive on these cells.