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Recent experimental advances in perovskite solar cell (PSC) technology marked a new era for low-cost, flexible, and high-efficiency photovoltaics (PVs). In contrast, the study of the detailed physical mechanisms governing the optoelectronic properties of PSCs has not been keeping up with these breakthroughs, which have been eclipsing theoretical efforts aimed at a more in-depth understanding of this emerging PV technology. Consequently, this has been hindering the design of the devices from reaching their maximum potential. The present article aims to bridge this gap by using a coupled optical and electrical modeling approach to optimize and rigorously assess the transport properties of selected photonic-structured PSC architectures, with particular attention given to ultrathin (300 nm) perovskite absorbers as they can pronouncedly benefit from the light-trapping effects provided by micro-structuring. The central finding of this study is that photonic-structured ultrathin PSCs benefit from significantly enhanced light in coupling and subsequent photocurrent generation in the absorber layer. This leads to more than 20% increase in the short circuit current in comparison with planar devices. In addition, slight increases in the open-circuit voltage and fill factor can be obtained due to the ultrathin perovskite absorbers, and thus, power conversion efficiencies approaching 30% are possible. Moreover, it was also found that the electrical simulations of complex 3D device geometries can be accurately simplified to 1D, massively benefiting the computational efficiency of these studies. published

Solar cells transparent in the visible range are highly requested for integration in see-through photovoltaic (PV) applications such as building glass façades or greenhouse roofs. The development of advanced transparent PV can fully exploit the tandem technology where the top cell absorbs the near-ultraviolet solar spectrum while the bottom one absorbs the near-infrared part. Herein, a possible implementation of this tandem PV paradigm, namely, the tandem structure composed of a high-bandgap halide perovskite solar cell and a low-bandgap organic solar cell, is considered. Electro-optical simulation results based on parameters calibrated on experimental data show that an efficiency of 15% can be achieved with an average visible transmittance above 50%. This can be obtained considering the halide perovskite with mixed chlorine and bromine anions, a nonfullerene-based bulk heterojunction, a well-calibrated light management, and a three-terminal configuration of the tandem.

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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 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.

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.

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.”

This work analyzes in detail the effect of ferroelectric polarization patterns in methylammonium lead iodide (MAPbI3) thin-films on the J-V characteristics of the corresponding solar cells. The simulations are based on a finite-element discretization of the drift-diffusion equations and take into account the polarization pattern experimentally derived from piezoresponse force micrographs. Based on the knowledge of the crystalline structure, symmetry considerations and electrical simulations, we discuss models for the polarization orientation pattern and magnitude of the ferroelectric domains. We conclude that the in-plane polarization vectors have 45° orientation towards the domain walls and form herring-bone structures. The presence of ordered ferroelectric domains, even with a weak characteristic polarization magnitude enhances the power conversion efficiencies and are mandatory to reproduce the experimental J-V characteristics.

In this work we review basic aspects of multiscale approaches for combining atomistic with continuous media descriptions and quantum mechanical with semiclassical drift---diffusion transport models for LED simulations. We show how hybrid coupling of the Green's function formalism with drift---diffusion simulations can give additional insight into device behaviour without compromising too much computational efficiency, and that the inclusion of atomistic tight-binding calculations in a multiscale framework can help in understanding specific features related to alloy fluctuations.

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.

In this work we demonstrate how a full comprehensive model can be used to understand the electrical behavior of actual organic devices. We address all the aspects which need to be taken into account for realistic simulations of a wide range of device structures and configurations. In particular we stress the relevance of the correct modeling of contact/organic interfaces. The model is applied to perform predictive simulations of organic light-emitting diodes and to deduce how a full experimental characterization of an organic device should be performed in order to completely grasp its electrical behavior.

In this article we highlight the necessity of atomistic based, fully quantum mechanical simulation approaches for modern electronic devices and their coupling with classical models. We review different ways of such couplings and provide application examples.

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.

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.

In this paper we present a multiscale framework for the simulation of electronic devices allowing the coupling of continuum and atomistic models in a transparent way. We introduce the basic features of the TiberCAD simulation software which is based on the multiscale simulation concept, and we show a simulation example to illustrate the basic aspects of a multiscale simulation.

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.

AlGaN/GaN and AlGaAs/InGaAs/GaAs HEMT structures are investigated theoretically to calculate the dependence of the 2DEG sheet resistance on strain. The inhomogeneous strain pattern induced by an external force is computed numerically using a continuous media model, assuming that the structures are grown on a thick substrate which remains unstrained. Current transport is simulated by means of a drift-diffusion model taking the spontaneous and piezoelectric polarization into account. The effect of strain onto the band structure is treated in the framework of k · p theory. The structures are simulated for different external pressures in order to study the relative change of resistance. The AlGaN/GaN structure shows an increasing resistance for increasing stress which can be related to the change of the piezoelectric polarization in the device. In the GaAs-based structure the effect depends on substrate termination and is more pronounced for B-face polarity.

We report on numerical simulations of a zincblende InP surface quantum dot (QD) on In Ga-0.48 P-0.52 buffer. Our model is strictly based on experimental structures, since we extrapolated a three-dimensional dot directly by atomic force microscopy results. Continuum electromechanical, (k) overarrow center dot (p) overarrow bandstructure and optical calculations are presented for this realistic structure, together with benchmark calculations for a lens-shape QD with the same radius and height of the extrapolated dot. Interesting similarities and differences are shown by comparing the results obtained with the two different structures, leading to the conclusion that the use of a more realistic structure can provide significant improvements in the modeling of QDs fact, the remarkable splitting for the electron p-like levels of the extrapolated dot seems to prove that a realistic experimental structure can reproduce the right symmetry and a correct splitting usually given by atomistic calculations even within the multiband (k) overarrow (p) overarrow. approach. Moreover, the energy levels and the symmetry of the holes are strongly dependent on the shape of the dot. In particular, as far as we know, their wave function symmetries do not seem to resemble to any results previously obtained with simulations of zincblende ideal structures, such as lenses or truncated pyramids. The magnitude of the oscillator strengths is also strongly dependent on the shape of the dot, showing a lower intensity for the extrapolated dot, especially for the transition between the electrons and holes ground state, as a result of a relevant reduction of the wave functions overlap. We also compare an experimental photoluminescence spectrum measured on an homogeneous sample containing about 60 dots with a numerical ensemble average derived from single dot calculations. The broader energy range of the numerical spectrum motivated us to perform further verifications, which have clarified some aspects of the experimental results and helped us to develop a suitable model for the spectrum, by assuming a not equiprobable weight from each dot, a model which is extremely consistent with the experimental data..

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.

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.

We present fully self-consistent simulation results based on an electro-thermo-mechanical model of a typical AlGaN/GaN HEMT structure. The mechanical stress state is analyzed under different dc operating conditions in view of possible dislocation formation and movement by comparing simulated elastic energy densities and resolved shear stresses with theoretically predicted values. In particular, we find nonzero resolved shear stress on all wurtzite slip systems, with relevant values especially at high dc power. This could allow formation and movement of dislocations, leading to device degradation.

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.

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 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.

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.