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The recent advances in chip-size microscopy based on optical scanning with spatially resolved nano-illumination light sources are presented. This new straightforward technique takes advantage of the currently achieved miniaturization of LEDs in fully addressable arrays. These nano-LEDs are used to scan the sample with a resolution comparable to the LED sizes, giving rise to chip-sized scanning optical microscopes without mechanical parts or optical accessories. The operation principle and the potential of this new kind of microscope are analyzed through three different implementations of decreasing LED dimensions from 20 µm down to 200 nm.

GaN-based light emitting diodes (LEDs) have been shown to effectively operate down to nanoscale dimensions, which allows further downscaling the chip-based LED display technology from micro- to nanoscale. This brings up the question of what resolution limit of the illumination pattern can be obtained. We show two different approaches to achieve individually switchable nano-LED arrays. We evaluated both designs in terms of near-field spot size and optical crosstalk between neighboring pixels by using finite difference time domain (FDTD) simulations. The numerical results were compared with the performance data from a fabricated nano-LED array. The outcome underlines the influence of geometry of the LED array and materials used in contact lines on the final illumination spot size and shape.

In this work we present a generalized transfer matrix method to study the effect of the photon recycling on the performance of solar cells. Photon recycling increases the charge carrier concentration in solar cells, resulting in an increase of the open circuit voltage $(V_{oc})$ . The model is based on the transfer matrix method (TMM), taking into account internal sources representing the emission from radiative recombination.

In lensless microscopy, spatial resolution is usually provided by the pixel density of current digital cameras, which are reaching a hard-to-surpass pixel size / resolution limit over 1 µm. As an alternative, the dependence of the resolving power can be moved from the detector to the light sources, offering a new kind of lensless microscopy setups. The use of continuously scaled-down Light-Emitting Diode (LED) arrays to scan the sample allows resolutions on order of the LED size, giving rise to compact and low-cost microscopes without mechanical scanners or optical accessories. In this paper, we present the operation principle of this new approach to lensless microscopy, with simulations that demonstrate the possibility to use it for super-resolution, as well as a first prototype. This proof-of-concept setup integrates an 8 × 8 array of LEDs, each 5 × 5 μm2pixel size and 10 μmpitch, and an optical detector. We characterize the system using Electron-Beam Lithography (EBL) pattern. Our prototype validates the imaging principle and opens the way to improve resolution by further miniaturizing the light sources. © 2020 Optical Society of America under the terms of theOSA Open Access Publishing Agreement

Motivated by possible application of InGaN/GaN multi-quantum well solar cells in hybrid concentrated photovoltaic / solar thermal power conversion systems, we have analyzed the temperature and intensity dependence of the open-circuit voltage of such devices up to 725 K and more than 1000 suns. We show that the simple ABC model routinely used to analyze the measured quantum efficiency data of InGaN/GaN LEDs can accurately reproduce the temperature and intensity dependence of the measured open-circuit voltage if a temperature-dependent Shockley–Read–Hall lifetime is used and device heating is taken into account.

In this work, we study the optical emission from arrays of InGaN/GaN MQW nanofin and nanorod arrays with sizes ranging from a few micrometers down to sub-wavelength dimensions (i.e., nanometers). Such systems are of interest for developing arrays of single addressable nanoLEDs, which could be used to obtain a visible wavelength super-resolution microscope where the resolution is due to highly localized light spots with sub-wavelength LED-to-LED pitch. We have used commercial full-wave Maxwell solvers (COMSOL, CST) to calculate the optical field emitted from a single nanoLED in a periodic array for a wavelength of 450 nm. Simulations on 11×11 nanoLED arrays with pitches of 200 nm up to 800 nm and diameters of down to 50 nm have been conducted, in which the dependency of the emission pattern on different structural parameters is studied. In case of small nanoLED array with very narrow pitch, a large optical cross-talk between the activated LED and its neighboring pixels was found. Moreover, in presence of cross-talks, test objects smaller than the LED pitch placed on its surface with influence of near field could potentially be resolved by evaluating the varied emission patterns obtained by different pixel activations. Routes to achieve higher localized optical fields and reduce optical cross-talk have been also investigated by modifying the nanoLED array structures (e.g., by introducing filling material among the LED pixels).

In this paper, we present a novel generalized multiparticle drift-diffusion (mp-DD) model capable to overcome some limitations imposed by the classic drift-diffusion model by taking into account multiple carrier populations. We demonstrate the model’s ability and flexibility in simulating systems from different application contexts. We conclude that the developed mp-DD model allows investigating a wide range of complex mechanisms, such as subband charge transport calculation or intersystem crossing (ISC), which are crucial for the understanding and design of organic and inorganic semiconductor devices largely employed for both photovoltaics and light emitting applications.

Recent research into miniaturized illumination sources has prompted the development of alternative microscopy techniques. Although they are still being explored, emerging nano-light-emitting-diode (nano-LED) technologies show promise in approaching the optical resolution limit in a more feasible manner. This work presents the exploration of their capabilities with two different prototypes. In the first version, a resolution of less than 1 µm was shown thanks to a prototype based on an optically downscaled LED using an LED scanning transmission optical microscopy (STOM) technique. This research demonstrates how this technique can be used to improve STOM images by oversampling the acquisition. The second STOM-based microscope was fabricated with a 200 nm GaN LED. This demonstrates the possibilities for the miniaturization of on-chip-based microscopes., This work was partially supported by the European Union’s Horizon 2020 research and innovation program under grant agreement No. 737089—ChipScope.

Metropolis Monte Carlo simulations are used to construct minimal energy configurations by electrostatic coupling of rotating dipoles associated with each unit cell of a perovskite CH3NH3PbI3 crystal. Short-range antiferroelectric order is found, whereas at scales of 8-10 nm, we observe the formation of nanodomains, strongly influencing the electrostatics of the device. The models are coupled to drift-diffusion simulations to study the actual role of nanodomains in the I-V characteristics, especially focusing on charge separation and recombination losses. We demonstrate that holes and electrons separate into different nanodomains following different current pathways. From our analysis we can conclude that even antiferroelectric ordering can ultimately lead to an increase of photoconversion efficiencies thanks to a decrease of trap-assisted recombination losses and the formation of good current percolation patterns along domain edges.

By combining optical and drift-diffusion models, a comprehensive simulation of power conversion efficiency of tandem solar cells is presented. To obtain consistent current–voltage characteristics of polymer tandem solar cells, the model takes into account correct description of organic–metal interfaces and organic semiconductor physics, in order to include the effect of interfaces and energetic disorder. A generalized methodology is developed to obtain the current–voltage characteristics of polymer tandem solar cells, which fully accounts for the interplay between the two subcells. The model is applied to the tandem cell with different commercially available polymers and for different subcell thicknesses and interconnection architectures. Based on the results of this model, it will be possible to design and optimize tandem structures toward higher efficiencies. Finally, it is concluded that the parallel configuration shows the highest performance over all studied cell structures.

We present and analyze a family of highly accurate quadrature-based Scharfetter-Gummel fluxes for charge carrier transport in semiconductors which are particularly useful for non-Boltzmann statistics.

Photovoltaics is amongst the most important technologies for renewable energy sources, and plays a key role in the development of a society with a smaller environmental footprint. Key parameters for solar cells are their energy conversion efficiency, their operating lifetime, and the cost of the energy obtained from a photovoltaic system compared to other sources. The optimization of these aspects involves the exploitation of new materials and development of novel solar cell concepts and designs. Both theoretical modeling and characterization of such devices require a comprehensive view including all scales from the atomic to the macroscopic and industrial scale. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Therefore, multiscale modeling has found particular interest in the photovoltaics community, as a tool to advance the field beyond its current limits. In this article, we review the field of multiscale techniques applied to photovoltaics, and we discuss opportunities and remaining challenges. © T. Abu Hamed et al., published by EDP Sciences, 2018., European Cooperation in Science and Technology: MP1406, The authors are grateful for the financial support by the COST Action MP1406 “MultiscaleSolar.”

Renewable energy sources are among the most important ingredients for the development of a human society with sustainable environmental footprint. Among these, photovoltaics (PV) plays a key role and is therefore a field of intense research. The key parameters of a solar cell technology includes not only the energy conversion efficiency but also the operating lifetime and the overall cost of the energy produced. The latter must also be compared with other energy sources. The optimization of all these different aspects involves research across the whole photovoltaics value chain, starting from material science up to system optimization. Development of new solar cell device concepts is as important as search for new materials with more suitable optoelectronic properties or improved approaches for PV module design and integration in power distribution systems. This requires a comprehensive view on PV technology across all scales, from the atomic to the macroscopic and industrial scale. An important aspect of PV research and of development of new devices and systems, is theoretical modeling as an indispensable tool for both basic understanding and device optimization. This involves modeling also on all scales, from the microscopic properties of materials and nanostructures up to the behavior of PV modules. During the last decade, multiscale approaches have seen increasing interest for application in numerical simulation of electronic devices. In particular, modeling and understanding of advanced photovoltaic devices are expected to benefit from multiscale modeling, which allows describing consistently both macroscopic device behavior and local microscopic processes governing light absorption, loss mechanisms, carrier transport, and extraction. In fact, many advanced PV concepts rely on effects or contain structural features that are insufficiently described by standard numerical simulation approaches or semianalytic models, both regarding electronic and optical properties. The different length scales of the electronic and optical degrees of freedoms specifically lead to an intrinsic need for multiscale simulation, which is accentuated in many advanced photovoltaics concepts including nanostructured regions. Moreover, the active layers in solar cells generally require to have a certain thickness and a large overall device area, in order to absorb a sufficient amount of light. This special issue is an attempt to collect articles on modeling of PV devices and systems on all scales. It includes two experimental articles, one shedding some light on photoreflectance measurements when probing above the pump beam energy and the other discussing morphology in hybrid lead halide perovskite solar cells. One article describes numerical modeling of Cu2O on Si tandem cells based on a semiempirical approach. A further contribution shows a physics-based model of a quantum dot solar cell, including a comparison with experimental data. The remaining two papers deal with system relevant aspects, namely, power point tracking and electrical inverters for connecting PV modules or power plants with appliances.

In this paper we present a multiscale simulation of charge transport in a solid-state dye-sensitized solar cell, where the real morphology between TiO2 and the hole transport material is included. The geometry of the interface is obtained from an electron tomography measurement and imported in a simulation software. Charge distribution, electric field and current densities are computed using the drift-diffusion model. We use this approach to investigate the electrostatic effect of trap states at the interface between the electron and hole transport materials. The simulations show that when the trapped electrons are not screened by external additives, the dynamics of holes is perturbed. Holes accumulate at the interface, enhancing recombination and reducing cell performance.

International audience; We present a study of blue III-nitride light-emitting diodes (LEDs) with multiple quantum well (MQW) and quantum dot (QD) active regions (ARs), comparing experimental and theoretical results. The LED samples were grown by metalorganic vapor phase epitaxy, utilizing growth interruption in the hydrogen/nitrogen atmosphere and variable reactor pressure to control the AR microstructure. Realistic configuration of the QD AR implied in simulations was directly extracted from HRTEM characterization of the grown QD-based structures. Multi-scale 2D simulations of the carrier transport inside the multiple QD AR have revealed a non-trivial pathway for carrier injection into the dots. Electrons and holes are found to penetrate deep into the multi-layer AR through the gaps between individual QDs and get into the dots via their side edges rather than via top and bottom interfaces. This enables a more homogeneous carrier distribution among the dots situated in different layers than among the laterally uniform quantum well (QWs) in the MQW AR. As a result, a lower turn-on voltage is predicted for QD-based LEDs, as compared to MQW ones. Simulations did not show any remarkable difference in the efficiencies of the MQW and QD-based LEDs, if the same recombination coefficients are utilized, i.e. a similar crystal quality of both types of LED structures is assumed. Measurements of the current–voltage characteristics of LEDs with both kinds of the AR have shown their close similarity, in contrast to theoretical predictions. This implies the conventional assumption of laterally uniform QWs not to be likely an adequate approximation for the carrier transport in MQW LED structures. Optical characterization of MQW and QD-based LEDs has demonstrated that the later ones exhibit a higher efficiency, which could be attributed to better crystal quality of the grown QD-based structures. The difference in the crystal quality explains the recently observed correlation between the growth pressure of LED structures and their efficiency and should be taken into account while further comparing performances of MQW and QD-based LEDs. In contrast to experimental results, our simulations did not reveal any advantages of using QD-based ARs over the MQW ones, if the same recombination constants are assumed for both cases. This fact demonstrates importance of accounting for growth-dependent factors, like crystal quality, which may limit the device performance. Nevertheless, a more uniform carrier injection into multi-layer QD ARs predicted by modeling may serve as the basis for further improvement of LED efficiency by lowering carrier density in individual QDs and, hence, suppressing the Auger recombination losses.

Filament-type HfO2-based RRAM has been considered as one of the most promising candidates for future non-volatile memories. Further improvement of the stability, particularly at the “OFF” state, of such devices is mainly hindered by resistance variation induced by the uncontrolled oxygen vacancies distribution and filament growth in HfO2 films. We report highly stable endurance of TiN/Ti/HfO2/Si-tip RRAM devices using a CMOS compatible nanotip method. Simulations indicate that the nanotip bottom electrode provides a local confinement for the electrical field and ionic current density; thus a nano-confinement for the oxygen vacancy distribution and nano-filament location is created by this approach. Conductive atomic force microscopy measurements confirm that the filaments form only on the nanotip region. Resistance switching by using pulses shows highly stable endurance for both ON and OFF modes, thanks to the geometric confinement of the conductive path and filament only above the nanotip. This nano-engineering approach opens a new pathway to realize forming-free RRAM devices with improved stability and reliability.

Following the experimental evidences of filament forming in organic thin film memories, we developed a semiclassical drift-diffusion model of electrical conductivity in the filament. We show that the global behavior of a memory device and the total current can be accounted for by fully-formed and well-connected filaments. We investigated and ruled out the eventual influence of coherent quantum tunneling in disconnected filaments. It is also shown how a heating model of the filament can be used to check if assumptions on the number of filaments and their radii are physically plausible.

White light emitting diodes (LEDs) based on III-nitride InGaN/GaN quantum wells currently offer the highest overall efficiency for solid state lighting applications. Although current phosphor-converted white LEDs have high electricity-to-light conversion efficiencies, it has been recently pointed out that the full potential of solid state lighting could be exploited only by color mixing approaches without employing phosphor-based wavelength conversion. Such an approach requires direct emitting LEDs of different colors, including, in particular, the green-yellow range of the visible spectrum. This range, however, suffers from a systematic drop in efficiency, known as the "green gap," whose physical origin has not been understood completely so far. In this work, we show by atomistic simulations that a consistent part of the green gap in c-plane InGaN/GaN-based light emitting diodes may be attributed to a decrease in the radiative recombination coefficient with increasing indium content due to random fluctuations of the indium concentration naturally present in any InGaN alloy.

Usually, the calculation of the optical generation in solar cell simulations is based on the assumption of constant absorption coefficients. Under certain circumstances, however, the absorption coefficient may depend on the light intensity, for example, if the absorbing material suffers from optical saturation. In this work, we present a simple model taking into account a saturable absorber, which can be easily implemented in standard optical simulation models.

Dye solar cells (DSCs) are a complementary type of solar cell devices, and particularly interesting because they can be assembled in new and more exotic architectures compared to conventional solar cells. These systems need to be simulated preserving the real geometry of the device. In this paper, we use a 3-D model of DSCs implemented using finite element method to simulate DSCs wrapped around an optical fiber. We focus on the investigation of the electrical behavior of the cell by changing three important aspects: the counter-electrode contact, TiO2 thickness and light coupling between the optical fiber and the active porous material in the cell.

Due to the downscaling of semiconductor device dimensions and the emergence of new devices based on nanostructures, carbon nanotubes and molecules, the classical device simulation approach based on semi-classical transport theories needs to be extended towards a quantum mechanical description. We present a simulation environment designed for multiscale and multiphysics simulation of electronic and optoelectronic devices with the final aim of coupling classical with atomistic simulation approaches.

We report on a multiscale simulation approach that includes both macroscopic drift-diffusion current model and quantum tunneling model. The models are solved together in a self-consistent way inside a single simulation package. As an example, we study the subthreshold transfer characteristics of MOS transistors based on high-κ oxides. We compare the high-κ gates based on HfO2 and ZrO2 with a SiO2 gate of the same equivalent thickness and show the effect of the tunneling current on transistor performance.

In this work we consider the effect of ferroelectric nanodomains on hybrid CH3NH3PbI3 perovskite solar cells. Two-dimensional models of ferroelectric domains are obtained with Metropolis Monte Carlo, considering one effective rotating dipole in each crystal cell. Transport properties of perovskite samples are obtained using drift-diffusion calculations, including local polarization field. We show that the presence of nanodomains have a strong impact on transport and charge carrier separation.

Material layers at electrode/semiconductor interfaces are fundamental for the photovoltaic properties of polymer solar cells. The relationship between open-circuit voltage (VOC) and the work function ($phi$) of these interface layers is still a matter of debate. Simulations, together with experiments on over more than 20 cell architectures based on P3HT:PC60BM, enabled us to analyze the physical dependence of VOC on $phi$. In particular, when the work function of the contacts is well inside the gap we observe that performance depends strongly on even small variations of $phi$. On the other hand, when it approaches the energy levels of the semiconducting polymers, device operation becomes the most efficient and less sensitive to variations in $phi$. Furthermore, by varying the Gaussian density of states (DOS) of the active blend we were able to show that VOC performance depends significantly also on the DOS. Our study based on the simultaneous variation of transport layers represents a promising method to optimize the design and performance of polymer solar cells.

cited By 0; International audience; We report on numerical simulations of quantum-dot heterostructures derived from experimental high-resolution transmission electron microscopy results. A real sample containing large InGaN islands with size of ten of nm and non-uniform In content is analyzed. The three-dimensional models for the quantum dots have been directly extrapolated from experimental results by a numerical algorithm. We show electromechanical, continuum k→ · p→, empirical tight-binding and optical calculations for these realistic structures, which present a very good agreement if compared with experimental measurements, implying that the use of realistic structures can provide significant improvements into the modeling and the understanding of quantum-dot nanostructures.

In this work we present a multiscale simulation of a solid state dye sensitized solar cell including the real morphology of the active layer. In order to include the real morphology the device domain is split into two different regions: one treated using an effective material approximation and another one using the real structure of the blend. The real morphology has been measured using electron tomography to reconstruct the mesoporous TiO 2 . The geometry was inserted into a mesher and used to solve a drift-diffusion model using finite element method. The simulation is used to cast light over morphology effects in solid state dye solar cells.

We discuss three different models of switching between the high conductivity and low conductivity state in organic bistable devices (OBD) with embedded nanoparticles. All models assume the same basic mechanism: charge trapping and de-trapping in metal nanoparticles. We show trapped charges can both induce an increase or a reduction of the total current depending on device configurations. The influence of energy disorder is investigated.

We present atomistic simulations of InGaN quantum disk and quantum well structures considering randomly distributed In atoms. It is shown that the random alloy fluctuations lead to an intrinsic broadening of the optical emission lines with an asymmetric tail towards long wavelengths. The amount of broadening is found to be dependent on In content.

We present a numerical model of quasi one-dimensional and quasi zero-dimensional semiconductor heterostructures strictly based on experimental structures of polyphorm cylindrical nanocolumns.

International audience; We report on a numerical model of quasi onedimensional and quasi zero-dimensional semiconductor heterostructures. This model is strictly based on experimental structures of cylindrical nanocolumns of AlGaAs grown by molecular-beam epitaxy in the (111) direction. The nanocolumns are of 20 - 50 nm in diameter and 0.5 - 1 ìm in length and contain a single GaAs quantum dot, of 2 nm in thickness and 15 - 45 nm in diameter. Since the crystal phase of these nanowires spontaneously switches during the growth from zincblende (Zb) to wurzite (Wz) structures we implement a continuum elastic model and 8 band ~k * ~p model for polymorph crystal structures. The model is used to compute electromechanical fields, wavefunction energies of the confined states and optical transitions. The model compares a pure Zb structure with a polymorph in which the Zb disk of GaAs is surrounded by Wz barriers and results are compared to experimental photoluminescence excitation spectra. The good agreement found between theory and features in the spectra supports the polyphorm model.

In this paper, we present simulation results on the optical and transport properties of InGaN/GaN core-shell nanorod light-emitting diodes. The influence of contact position, surface recombination, and doping configuration on internal quantum efficiency is examined. The qualitative behavior when adding an electron blocking layer and the dependence on In content have been studied.

International audience; The impact of electromechanical coupling on optical properties of light-emitting diodes (LEDs) with InGaN/GaN quantum-dot (QD) active regions is studied by numerical simulations. The structure, i.e. the shape and the average In content of the QDs, has been directly derived from experimental data on out-of-plane strain distribution obtained from the geometric-phase analysis of a high-resolution transmission electron microscopy image of an LED structure grown by metalorganic vapor-phase epitaxy. Using continuum $\vec{k}\cdot \vec{p}$ calculations, we have studied first the lateral and full electromechanical coupling between the QDs in the active region and its impact on the emission spectrum of a single QD located in the center of the region. Our simulations demonstrate the spectrum to be weakly affected by the coupling despite the strong common strain field induced in the QD active region. Then we analyzed the effect of vertical coupling between vertically stacked QDs as a function of the interdot distance. We have found that QCSE gives rise to a blue-shift of the overall emission spectrum when the interdot distance becomes small enough. Finally, we compared the theoretical spectrum obtained from simulation of the entire active region with an experimental electroluminescence (EL) spectrum. While the theoretical peak emission wavelength of the selected central QD corresponded well to that of the EL spectrum, the width of the latter one was determined by the scatter in the structures of various QDs located in the active region. Good agreement between the simulations and experiment achieved as a whole validates our model based on realistic structure of the QD active region and demonstrates advantages of the applied approach.

The purpose of this work is to present a complete drift-diffusion model for a dye solar cells (DSCs) and to correlate numerical simulation with experimental efficiency of the cell, stressing the influence of the active layer thickness. We focus on two fundamental microscopic parameters, namely, the electron diffusion coefficient and the recombination rate constant, which are extracted by a proper simulation fitting of the experimental IV curves of four different sets of DSCs. Both the conduction band model and the multiple trapping model are considered in the fitting procedure. We show that a given set of parameters is able to fit the behavior of the cell under different illumination conditions. Conversely, parameters need to be varied to fit IV curves of cells with different TiO2 thicknesses. The calculated effective diffusion length show a dependence on the working point and on the model used to simulate the cell. This work, moreover, gives a solid numerical ground for neglecting the electronic drift co...

In this work, we use the multiscale software tool TiberCAD to study the electronic and optical properties of InGaN-quantum-disk (QD)-based GaN nanocolumn p-i-n diode structures. Strain maps show a clear relaxation effect close to the column boundaries; however, results from full self-consistent 3-D quantum calculations indicate that emission is focused in the center of the QD and emission energy is little depending on the column size. Moreover, the effect of surface states on transport is largely reduced when quantum densities are taken into account, since current in the nanocolumn light emitting diode (LED) results to flow mainly in the QD region. Nanocolumn geometry appears to be quite robust against variation of lateral scale, while it is largely sensitive to the QD alloy composition.

In this work we use the multi-scale software tool tiberCAD to study the electronic and optical properties of a InGaN quantum disk (QD) in a GaN nanocolumn p-i-n diode structure, both with a macroscopical and an atomistic approach. Results show that the strain relaxation close to the lateral surface is evident for smaller nanocolumns but its effect tends to vanish for higher values of the column width. Self-consistent Schrodinger–Poisson/drift-diffusion calculations show that particle density and therefore radiative recombination rate are focused in the center of the QD (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this work we present a Computer Aided Design (CAD) software, called TiberCAD, to simulate Dye Sensitized Solar Cells (DSC). DSCs are particularly interesting devices due to their high efficiency (more than 11% on small area and 8% on large area) and long stability. Since their first development, much progress has been made in terms of efficiency, stability, lifespan and engineering of the device. However, the field of DSCs still lacks a complete model able to simulate the entire device over a general domain including all its components. In our model a drift-diffusion set of equations for the different charge carriers coupled to Poisson equation has been implemented within finite element method. The model takes into account also trap assisted transport for electrons in the mesoporous titanium dioxide with a phenomenological model derived from multi-trapping model. Three different applications of the code in 1, 2 and 3D are presented. The first 1D simulation is a study of correlation between physical parameters of the cell and energy conversion efficiency. A second application, 2D, discusses the effect on density and current distributions for different contacting of the cell and loss induced by the shadowing of metallic fingers. Finally, the third case, 3D, presents two different and innovative topologies for a DSC. A cell where contacts and illumination surface are completely decoupled and a DSC wrapped around an optical fiber.

Dye Sensitized solar cells (DSC) are an interesting alternative to conventional silicon based solar cells. Although DSCs are very close to be commercialized, still many issues need to be addressed. Part of the problem is related to the lack of a reliable and consistent simulator able to catch the physics and the chemistry underlining the functioning of the cell. The need of a reliable simulator and modelling is particularly important for the engineering of the cell and to define trends not only in the component characteristics, but also in the building of the device. Among the different parts which compone a DSC the relevance of semiconductor titanium oxide substrate can hardly be underestimated. TiO 2 is where the dye molecule is chemisorbed and where the recombination occurs. Moreover, changes in the topology of the semiconductor paste can lead to other smaller effects in the total efficiency. In this paper we investigate the effects of changing working parameters for the titanium oxide and varying its topology. The simulations are performed using a finite element code based on TiberCAD software1 to describe in details the electrical properties of the cell. The CAD allows to calculate steady-state properties and ideal I-V characteristics of the cell solving a set of differential equations on meshes in 1, 2 and 3 dimensions.

Using solar power is one of the most important challenge of today technology. A big effort is devoted in going beyond traditional semiconductor, especially silicon based, solar cells. A well established and promising technology is represented by electrochemical dye solar cells (DSC). Their functioning is a complicated interplay of different parts deeply interconnected which requires a model able to catch the whole device and the different processes at the same time. We develop an extension to the TiberCAD code to simulate such kind of devices.

In this paper we present an electrical model to simulate a Dye sensitized Solar Cell (DSC) based on a Finite Element Method as an extension of the TiberCAD code. The CAD allows to calculate steady-state properties and ideal IV characteristic of the cell using 1, 2 and 3D meshes for the device. We describe the model and its prerogatives, explaining the code-related problems and the implementation of the model. We show a comparison with a measured IV curve, shading light on revealing the role of different parameters involved in the physics of conversion of light. Finally, an application to an experimental set-up, the Incident Photon to Current Efficiency, is presented, estimating the Collection Efficiency spectrum for a standard DSC and the collection efficiency spectrum for a standard DSC.

We report on numerical simulations of InP surface lateral quantum-dot molecules on In0.48Ga0.52 P buffer, using a model strictly derived by experimental results by extrapolation of the molecules shape from atomic force microscopy images. Our study has been inspired by the comparison of a photoluminescence spectrum of a high-density InP surface quantum dot sample with a numerical ensemble average given by a weighted sum of simulated single quantum-dot spectra. A lack of experimental optical response from the smaller dots of the sample is found to be due to strong inter-dot strain fields, which influence the optoelectronic properties of lateral quantum-dot molecules. Continuum electromechanical, k→·p→ bandstructure, and optical calculations are presented for two different molecules, the first composed of two dots of nearly identical dimensions (homonuclear), the second of two dots with rather different sizes (heteronuclear). We show that in the homonuclear molecule the hydrostatic strain raises a potential ...

We report on the anisotropic electro-optic response of sputtered ZnO films and its dispersion towards both the frequency of the modulating voltage and the wavelength of the probing beam. The observed dispersion put in evidence two mechanisms. A fast and weak electrorefraction response, due to the nonlinear polarization of bound electrons, and a strong and slow carrier refraction term, ascribed to the modulation of free carriers. The former corresponds to an electro-optical coefficient of approximately −0.5 pm/V, while the latter may reach a magnitude up to 20 times stronger. This term relaxes at about 12 kHz and is largely wavelength dependent, due to a combination of effects. Also bias voltages lead to its quenching, likely extending the depletion regions at grain boundaries.

Liquid-phase exfoliation of zirconium trisulfide (ZrS3) was used to produce stable and ready-to-use inks for solution-processed semiconductor thin-film deposition. Ribbon-like layered crystals of ZrS3 were produced by the chemical vapor transport method and were then exfoliated in three different solvents: dimethylformamide, ethanol, and isopropyl alcohol. The resulting ZrS3 dispersions were compared for stability and the ability to form continuous films on top of the perovskite layer in light-emitting diodes with the ITO/PEDOT:PSS/MAPbBr3/2D-ZrS3/LiF/Al structure. Film deposition was performed by using either spray or slot-die coating methods. The slot-die coating route proved to produce better and more uniform films with respect to spray coating. We found that the 2D ZrS3 electron injection layer (EIL) stabilized the interface between the perovskite and LiF/Al cathode, reducing the turn-on voltage to 2.8 V and showing a luminance that does not degrade during voltage sweep. On the other hand, EIL-free devices show electroluminescence on the first voltage sweep that reduces almost to zero in the subsequent sweeps. Combining physical device simulation and density functional theory calculation, we are able to explain these results in terms of lowering the electron injection barrier at the cathode.

New nano-illumination microscopy instrumentation will be presented together with the road to overcome the diffraction limit in order to achieve super-resolution. The simplicity of this technique would make it suitable in any low-resource scenario.

A universal simulation tool for electronic devices based on a semi-classical drift-diffusion (DD) model is presented. The core of the model is a fully-coupled system of Poisson equation for the electrostatic potential and drift-diffusion transport equations. Both charged and neutral (e.g. excitons) carriers are supported. One transport equation is associated to each carrier. The number of carriers can be set at user level. The equation system can be defined in 1, 2 and 3 dimensions, and it is solved using finite element methods (FEM). The simulator has many potential application, from simple semiconductors with electrons and holes transport, to far more complex device structures, such as the host-guest system of an OLED emitter layer including singlet and triplet excitons. The simulation of an OLED emitter layer is presented, including the thermally activated delayed fluorescence (TADF) effect.