Search

Plasmonic Cu nanoparticles were in-situ grown into a Cu$_2$O semiconductor matrix by using reactive magnetron sputtering and adjusting the amount of oxygen available during the synthesis in order to prevent the oxidation of part of copper atoms landed on the film surface. Varying only the oxygen flowrate (OFR) and using a single Cu target it was possible to observe the evolution in the simultaneous formation of metallic Cu and Cu$_2$O phases for oxygen-poor conditions. Suchformation is accompanied by the development of the surface plasmon band (SPB) corresponding to Cu, as evidenced by UV-Vis spectrophotometry and spectroscopic ellipsometry. The bandgap values of the elaborated composites containing embedded Cu plasmonic nanodomains were lower than the bandgap of single-phased Cu$_2$O films, likely due to the higher defect density associated to the nanocrystalline nature of films, promoted by the presence of metallic Cu. The resistivity of the thin films increased with more oxidative deposition conditions and was associated to an increase in Cu$_2$O/Cu ratio and smaller and more isolated Cu particles, as evidenced by high resolution transmission electron microscopy and X-ray diffraction. Photoconversion devices based on the studied nanocomposites were characterized by I-V and spectral photocurrent measurements, showing an increase in the photocurrent density under light illumination as consequence of the plasmonic particles excitation leading to hot carrier's injection in the nearby ZnO and Cu$_2$O semiconductors., Comment: ACS Applied Electronic Materials, American Chemical Society, 2022

In this work were elaborated thin films of Zinc Magnesium Oxide (ZnMgO) by ultrasonic spray pyrolysis. Zn(1-x)Mg(x)O is a wide bandgap compound semiconductor with useful properties for optoelectronic devices, mainly ultraviolet “solar-blind” detectors, as an active layer, and solar cells where it can be used as a buffer layer. The main difficulties related to the elaboration of Zn(1-x)Mg(x)O using solution-based and spray pyrolysis techniques are the wide miscibility gap between MgO and ZnO and the use of toxic and unsafe solvents such as methanol. In this study, we were able to elaborate Zn(1-x)Mg(x)O with varying Mg content up to 70% with water-based solutions only. The difficulty using only water-based solutions is related to the inherent unfavorable properties such as strong hydrogen bonds with high boiling point. However, we managed to optimize the precursors solution concentration, the number of scans, the flow rate, the pressure and the temperature, to obtain homogeneous and good quality films. The solid composition in the thin films was measured using X-ray fluorescence to assess the Mg solubility limit in Zn(1-x)Mg(x)O and its incorporation efficiency. High transmittance of about 90 % in the visible region was obtained in all the films with a very small variation with the thickness, suggesting a highly controlled process of the elaboration.The bandgap and the Urbach energy variation with the composition were investigated and linked to the morphology and structural properties. A miscibility limit of 30 % of Mg was obtained, confirmed by the X-ray fluorescence measurements and correlated to the bandgap variation with the Mg composition extracted from the transmittance spectra analysis. The structural properties were investigated using confocal micro-Raman spectroscopy which permitted to identify the wurtzite structure as the only phase in all the films with composition less than 30 %, with a phase separation occurring beyond this limit. The electrical properties were characterized using the van der Pauw and Hall effect technique using indium to form the ohmic contacts. The n-type carrier concentration dramatically decreases from about 2*10^(19) to 5*10^(15) cm^(-3) when increasing Mg composition from 0 % to 7 %. The thin films become semi-insulating for Mg composition higher than 7 %. The correlation of the electrical results with the optical and structural properties suggests that, in addition to the increase of the bandgap, a compensation mechanism related to the defects introduced in the alloy plays a central role in the decrease in the carrier concentration. The mobility slightly increases with the Mg composition suggesting that the films crystal quality was not significantly degraded by the increase of the magnesium composition in the considered range. The modulation of the conductivity, in addition and partially related to the modulation of the bandgap, is of high interest to the detector or the solar cell device.

Numerical simulations of AZO/Zn1−xGexO/Cu2O solar cell are performed in order to model for the first time the impact of the germanium composition of the ZnGeO buffer layer on the photovoltaic conversion efficiency. The physical parameters of the model are chosen with special care to match literature experimental measurements or are interpolated using the values from binary metal oxides in the case of the new Zn1−xGexO compound. The solar cell model accuracy is then confirmed thanks to the comparison of its predictions with measurements from the literature that were done on experimental devices obtained by thermal oxidation. This validation of the AZO/Zn1−xGexO/Cu2O model then allows to study the impact of the use of the low cost, environmental friendly and industrially compatible spray pyrolysis process on the solar cell efficiency. To that aim, the Cu2O absorber layer parameters are adjusted to typical values obtained by the spray pyrolysis process by selecting state of the art experimental data. The analysis of the impact of the absorber layer thickness, the carrier mobility, the defect and doping concentration on the solar cell performances allows to draw guidelines for ZnGeO/Cu2O thin film photovoltaic device realization through spray pyrolysis.

Purpose The purpose of this paper is to investigate the effect of growth temperature on the evolution of indium incorporation and the growth process of InGaN/GaN heterostructures. Design/methodology/approach To examine this effect, the InGaN/GaN heterostructures were grown using Taiyo Nippon Sanso Corporation metal-organic chemical vapor deposition (MOCVD) SR4000-HT system. The InGaN/GaN heterostructures were epitaxially grown on 3.4 µm undoped-GaN (ud-GaN) and GaN nucleation layer, respectively, over a commercial 2” c-plane flat sapphire substrate. The InGaN layers were grown at different temperature settings ranging from 860°C to 820°C in a step of 20°C. The details of structural, surface morphology and optical properties were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), atomic force microscopy and ultraviolet-visible (UV-Vis) spectrophotometer, respectively. Findings InGaN/GaN heterostructure with indium composition up to 10.9% has been successfully grown using the MOCVD technique without any phase separation detected within the sensitivity of the instrument. Indium compositions were estimated through simulation fitting of the XRD curve and calculation of Vegard’s law from UV-Vis measurement. The thickness of the structures was determined using the Swanepoel method and the FE-SEM cross-section image. Originality/value This paper report on the effect of MOCVD growth temperature on the growth process of InGaN/GaN heterostructure, which is of interest in solid-state lighting technology, especially in light-emitting diodes and solar cell application.

International audience; In this study, InGaN/GaN heterostructures were grown using metal organic vapor deposition (MOCVD) at different temperatures (800°C, 750°C and 700°C). The structural, crystallinity, surface morphology and optical properties were investigated using X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM) and ultraviolet-visible (UV-Vis) spectrophotometer, respectively. From observation, it is found that the indium composition was obtained from XRD through the process of fitting of the simulation. The process of indium incorporation is found to be sensitive to temperature variances. When the temperature is further reduced, the indium incorporation process would become stagnant as the decomposition process of ammonia would be less efficient. FE-SEM images have revealed surface-related defects such as V-pits. The secondary energy gap is obtained from the optical characterization which confirmed the incorporation of indium in the epilayers.

International audience; The Indium Gallium Nitride (InGaN) alloy has the required potentialities to be a material of choice used in the next generation high efficiency solar cells. Indeed, the mere change in its Indium composition allows its absorption to cover the whole solar spectrum. The other main advantages of InGaN, in addition to its tunable bandgap, are a high absorption coefficient, a high stability and radiation tolerance. However, challenging issues remain to address: (i) the difficulty to elaborate sufficiently thick monocrystalline InGaN layers with a high Indium content; (ii) the high defects density and the spontaneous and piezoelectric polarizations; (iii) the p-doping which remains difficult to master. A review of this promising technology for solar cells is provided and present challenges and future perspectives are presented, including the use of InGaN multijunction structures and a new InGaN Schottky Based Solar Cells (SBSC) structure.

International audience; This article presents Solis, a new modular, fast, and portable one-dimensional (1D) semiconductor device simulator designed and developed particularly for photovoltaic solar cells. Solis is coded in standard C++, runs natively on Windows and Linux, and is freely available to download. All the physical models and excitation parameters can be fully controlled using the fast embedded Lua scripting engine. Solis includes a useful set of tools coded in C, such as a code editor, graphical device editor, and data plotter. A material parameters database including well-known semiconductors and their alloys is also included. The Solis calculation engine implements the drift–diffusion transport model and takes into account indirect recombination processes (with user-defined deep or shallow levels) as well as radiative and Auger recombination. The anode and cathode parameters, including the refractive index, extinction coefficient, recombination speed, and barrier height for the Schottky contact, are fully included. It natively handles spontaneous and piezoelectric polarization, which is key for the development of devices based on wurtzite materials. The values of all the material parameters can be graded arbitrarily in position, offering flexibility for the simulation of heterostructure solar cells. In addition, Solis offers functionality needed by researchers to analyze the simulation results, including graphing (of the band diagram, carrier concentration, ionized dopant and trap concentrations, current–voltage and capacitance–voltage characteristics, quantum efficiency, etc.) with complete control of the graph and a useful mathematical console. Solis simulation results for a solar cell using Earth-abundant elements are presented herein. One of the main issues in the development of such solar cells, viz. the inhomogeneity due to phase separation in the absorber, is highlighted.

International audience; In this work, ZnO films are deposited by the ultrasonic spray pyrolysis technique on soda lime glass substrates by following a specific design of experiment. The ZnO films are spray deposited using different elaboration parameters. Optical, morphological, structural and electrical properties of the ZnO films are systematically investigated. Fourier-transform infrared and transmittance spectra are measured to examine their optical properties. They are correlated to their structural properties determined by X-ray diffraction and Raman spectroscopy. The surface morphology is analyzed using atomic force microscopy while the electrical conductivity is measured using the four probe technique. This comprehensive analysis shows that ZnO thin films elaborated using ultrasonic spray pyrolysis with fast growth rate have a high transparency in a wide thickness range, making them suitable for use in applications such as all-oxide solar cells.

International audience; The development of cost-effective solar cells requires on the one hand to master the elaboration techniques, and on the other hand, an adequate design to optimise the photovoltaic efficiency. These two research topics are closely linked and their association in the research work is the key in the development of novel thin film solar cells. The design associated with numerical optimisation gives the set of optimal physical and geometrical parameters, taking into account the technological feasibility. This will allow elaboration to target the most efficient structures in order to speed up the final device realisation. In this work, we used a new approach, based on rigorous multivariate mathematical global Bayesian algorithm, to optimise a Schottky based solar cell (SBSC) using InGaN as the absorber. The obtained photovoltaic efficiency is close to the conventional structures efficiency while being less complex to elaborate. In addition, the results have shown that the optimised SBSC structure exhibits high fabrication tolerances.

International audience; The challenge of switching for photovoltaic as a major source of electricity can only be fulfilled by using solar cells based on low toxicity and earth abundant materials combined with a low cost process. One of the most promising solution to achieve this goal is to use a metal oxide absorber such as cuprous oxide (Cu2O). In 2016, a Cu2O/ZnGeO solar cell was demonstrated by the Minani group and reached a record efficiency of 8.1%. A recent modeling of Cu2O solar cells by Rizi et al. confirms that ZnGeO buffer layer outperforms other buffer layers reported experimentally due to a better band alignement. However the experimental and simulated results were obtained by taking into account a solar cell based on a high demanding energy process (T>1000°C). Cuprous oxide thin films have already been developed by low cost and large area compatible processes, but currently in detriment of material quality with grain size in the range of tenth of nanometers and mobility two order of magnitude lower. In order to evaluate the impact of low cost processes on solar cell performances, we analyse the modelisation results of Cu2O/ZnGeO solar cell by carefully taking into account experimental material properties, defects and grain size of Cu2O grown by low cost processes. The conclusion of this analysis will serve as a guideline for solar cells elaboration by spray pyrolysis in our laboratory and measurements of device performances will be compared with our simulated results.

Gallic acid (GA) is involved in many biochemical processes and reactions and is of great importance in environment thanks to its antioxidant and pro-oxidant properties. We present in this paper a comprehensive study of GA deprotonation by means of Raman spectroscopy. In the Raman spectra, we identified the characteristic bands that were sensitive to the five pH-dependent GA forms. From these results, we extracted the GA pKa values that are consistent with the reference values. These results permit the monitoring of GA forms for applications. Copyright © 2015 John Wiley & Sons, Ltd.

International audience; The performance of a double heterojunction solar cell based on Indium Gallium Nitride (InGaN) including a tunnel junction was simulated. The most challenging aspects of InGaN solar cells development being the crystal polarization and structural defects detrimental effects, their impact on the solar cell performances has been investigated in detail. The solar cell simulation was performed using physical models and InGaN parameters extracted from experimental measurements. The optimum efficiency of the heterojunction solar cell was obtained using a multivariate optimization method which allows to simultaneously optimize eleven parameters. The optimum defect free efficiency obtained is 24.4% with a short circuit current J SC = 12.92mA/cm 2 , an open circuit voltage V OC = 2.29V and a fill factor FF = 82.55%. The performances evolution as functions of the polarization and the defects types and parameters was studied from their maximum down to as low as a 2% efficiency.

We analyzed and discussed the influence of thickness and doping concentration of the different layers in a-Si(p)/c-Si(n)/a-Si(n) photovoltaic (PV) cells with the aim of increasing its efficiency while decreasing its global cost. Compared to the efficiency of a standard marketed PV cell, elaborated with a ZnO transparent conductive oxide (TCO) layer but without Back Surface Field (BSF) layer, an optimization of the thickness and dopant concentration of both the emitter a-Si(p) and absorber c-Si(n) layers will gain about 3% in the global efficiency of the cell. The results also reveal that with introduction of the third layer, i.e. the BSF layer, the efficiency always achieves values above 20% and all other parameters of the cell, such as the open-circuit voltage, the short-circuit current and the fill-factor, are strongly affected by the thickness and dopant concentration of the layers. The values of all parameters are given and discussed in the paper. Thereby, the simulation results give for an optimized a-Si(p)/c-Si(n)/a-Si(n) PV cells the possibility to decrease the thickness of the absorber layer down to 50 ?m which is lower than in the state-of-the-art. This structure of the cell achieves suitable properties for high efficiency, cost-effectiveness and reliable heterojunction (HJ) solar cell applications.

International audience; Owing to its good tolerance to radiations, its high light absorption and its Indium-composition-tuned bandgap, the Indium Gallium Nitride (InGaN) ternary alloy is a good candidate for high--efficiency--high--reliability solar cells able to operate in harsh environments.Unfortunately, InGaN p-doping is still a challenge, owing to InGaN residual n-doping, the lack of dedicated acceptors and the complex fabrication process itself. To these drawbacks can be added the uneasy fabrication of ohmic contacts and the difficulty to grow the high-quality-high-Indium-content thin films which would be needed to cover the whole solar spectrum. These drawbacks still prevent InGaN solar cells to be competitive with other well established III-V and silicon technologies.In this communication, a new Metal-IN (MIN) InGaN solar cell structure is proposed, where the InGaN p-doped layer is removed and replaced by a Schottky contact, lifting one of the above mentioned drawbacks. A set of realistic physical models based on actual measurements is used to simulate and optimize its behavior and performance using mathematically rigorous multi-criteria optimization methods, aiming to show that both efficiency and fabrication tolerances are better than the previously described simple InGaN Schottky solar cell.

On the road towards next generation high efficiency solar cells, the ternary Indium Gallium Nitride (InGaN) alloy is a good passenger since it allows to cover the whole solar spectrum through the change in its Indium composition. The choice of the main structure of the InGaN solar cell is however crucial. Obtaining a high efficiency requires to improve the light absorption and the photogenerated carriers collection that depend on the layers parameters, including the Indium composition, p-and n-doping, device geometry.. . Unfortunately, one of the main drawbacks of InGaN is linked to its p-type doping, which is very difficult to realize since it involves complex technological processes that are difficult to master and that highly impact the layer quality. In this paper, the InGaN p-n junction (PN) and p-in junction (PIN) based solar cells are numerically studied using the most realistic models, and optimized through mathematically rigorous multivariate optimization approaches. This analysis evidences optimal efficiencies of 17.8% and 19.0% for the PN and PIN structures. It also leads to propose, analyze and optimize player free InGaN Schottky-Based Solar Cells (SBSC): the Schottky structure and a new MIN structure for which the optimal efficiencies are shown to be a little higher than for the conventional structures: respectively 18.2% and 19.8%. The tolerance that is allowed on each parameter for each of the proposed cells has been studied. The new MIN structure is shown to exhibit the widest tolerances on the layers thicknesses and dopings. In addition to its being player free, this is another advantage of the MIN structure since it implies its better reliability. Therefore, these new InGaN SBSC are shown to be alternatives to the conventional structures that allow removing the p-type doping of InGaN while giving photovoltaic (PV) performances at least comparable to the standard multilayers PN or PIN structures., Comment: Superlattices and Microstructures, Elsevier, 2016

Long format oral presentationChair of Session I: Nanomaterials Fabrication / Synthesis in Nanotech France 2016Chair of Session I: NanoEnergy in NanoMatEn 2016 associated conference; International audience; The Indium Gallium Nitride III-N alloy has the required potentialities to be a material of choice used in the next generation high efficiency solar cells. Indeed, the mere change in its Indium composition allows its absorption to cover the whole solar spectrum. One of InGaN main challenges remains today its p-doping. We therefore propose a comparative study between PN and PIN thin films structures, alongside new Schottky based designs which allow the removal of the difficult p-layer. A mathematically rigorous multi-criteria structure optimization associated to a 2D simulation based on actually measured physical parameters and precise models lead to theoretical efficiencies of 17.8%, 19.0%, 18.2% and 19.8% respectively for the PN, PIN, Schottky and a new proposed Metal-IN (MIN) Schottky based structure. The tolerance that is allowed on each parameter for each of the proposed cells has been thoroughly studied. These studies have shown that the new MIN structure exhibits high fabrication tolerances. This is particularly true for the n-doping of its n-layer, which can be raised enough, without loss of efficiency, to realize good low resistance ohmic contacts.Therefore, these new InGaN Schottky Based Solar Cells (SBSC) are shown to be efficient and tolerant alternatives to the conventional structures, allowing the removal of the p-type doping of InGaN while giving photovoltaic (PV) performances comparable to the highest reported thin films Solar Cell efficiencies.

International audience; The Indium Gallium Nitride (InGaN) III-Nitride ternary alloy has the potentiality to allow achieving high efficiency solar cells through the tuning of its band gap by changing the Indium composition. It also counts among its advantages a relatively low effective mass, high carriers' mobility, a high absorption coefficient along with good radiation tolerance. However, the main drawback of InGaN is linked to its p-type doping, which is difficult to grow in good quality and on which ohmic contacts are difficult to realize. The Schottky solar cell is a good alternative to avoid the p-type doping of InGaN. In this report, a comprehensive numerical simulation, using mathematically rigorous optimization approach based on state-of-the-art optimization algorithms, is used to find the optimum geometrical and physical parameters that yield the best efficiency of a Schottky solar cell within the achievable device fabrication range. A 18.2% efficiency is predicted for this new InGaN solar cell design.

Conducting polymer composites, which are simply physical mixtures of an insulating polymer matrix and intrinsically conducting polymers, are promising new materials for various applications such as antistatic coatings, shielding and electromagnetic absorbers. In this context, a novel conducting composite was successfully produced. It is based on epoxy resin and polyaniline (PANI) doped in benzene sulfonic acid, which was used as conducting filler. The effect of PANI loading levels on the structural, morphological, thermal, electrical and dielectric properties was explored using techniques, such as Raman, Fourier transform infrared and ultraviolet-visible-NIR spectroscopy, X-ray diffraction, atomic force microscopy, scanning electron microscopy, thermogravimetric analysis and differential scanning calorimetry. The electrical behavior and morphology of the synthesized PANI revealed disorder and defects. In addition, as the applied voltage is increased, the current through the sample increases rapidly. The conductivity and dielectric properties were also investigated at room temperature in the frequency range of 1 MHz–1 GHz. The dielectric constant was shown to increase with increased loading at low frequencies and then decreases rapidly, reaching a constant value at higher frequencies. In addition, the AC conductivity of the prepared composites increases with the addition of PANI and is higher at high frequencies. Furthermore, the stability of the composites was found to be influenced by increasing the amount of PANI filler in the matrix. The defects and heterogeneous system of polyaniline (PANI) doped in benzene sulfonic acid (BSA) with a crystalline region dispersed in an amorphous low-conducting region as shown in the scanning electron microscopy micrograph reveal the current–voltage characteristic, which shows a nonohmic variation. It increases in current with applied voltage owing to the conduction mechanisms of PANI due to the formation of polarons and bipolarons. As the applied voltage increases, the formation of polarons and bipolarons increases rapidly, contributing to higher values of current through sample. This characteristic affects the dielectric behaviors of the elaborate composites.

The InGaN ternary alloy has the potentiality to achieve high efficiency solar cells. Indeed the bandgap of the InGaN alloy covers the whole solar spectrum including the visible region by changing the Indium composition. The InGaN alloy also counts among its advantages a relatively low effective mass of electrons and holes, their high mobilities, high absorption coefficients as well as radiation tolerance. These very promising characteristics give the possibility to design and develop next-generation high-efficiency thin films solar cells, based on multijunction technology. However, the main drawback is the difficulty of p-doping and the high defects density in these III-Nitride alloys. In this report, we develop a novel and rigorous optimization approach based on state-of-the-art optimization algorithms, to design an optimal multijunction solar cell based on InGaN alloys. This approach allows to automatically determine the values of the cell parameters, among which are the geometries of the active layers, their doping and defect levels, to maximize its efficiency within the possibilities of actual device fabrication. We have found that the use of this rigorous optimization approach is necessary because of the high dependence of the cell efficiency on the device geometry, doping and defects, particularly concerning the top and bottom P layers properties

In this report, we study, by means of numerical simulation, the impact of the active layer properties and device geometry on the performance of the “solar blind” UV MSM detector based on AlGaN and BGaN alloys. The parameters investigated, using the Silvaco Athena and Atlas tools, were: (i) the Schottky contact width and thickness; (ii) the ternary (AlGaN or BGaN) physical properties, including the active layer thickness, n-type doping concentration and traps density. We implement the physical models and the ternary material properties, taken from literature or, if not available (as for the new BGaN ternary), from the interpolation between the binary materials weighted by the mole fractions. We have found that: (i) the photocurrent is highly improved by optimizing the device geometry, in particular the Schottky contact semi-transparency (depending on the contact thickness and metal absorption spectrum) and width; (ii) the doping and traps highly impact the device spectral response, and, in particular, a compromise in the doping concentration must be reached in order to maximize the detector performances; (iii) the incorporation of a small amount of boron in the active layer improves the detector spectral response. These results give us a powerful tool in order to understand quantitatively the impact of elaboration and processing conditions on the photodetector characteristics and thus identify the key issues in technology development (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

International audience; Large internal gains that can be obtained in wide band gap semiconductors-based (GaN and ZnO types) Schottky and/or metal-semiconductor-metal photodetectors are generally accompanied by large dark current and time response. We show that, using quasi-alloy of BGaN/GaN superlattices as the active layer, the dark current can be lowered while maintaining high internal gain (up to 3 x 10(4)) for optical power in the nW range and low time response (few tens of ns) for optical power in the W range. Furthermore, the boron incorporation allows the tuning of the cutoff wavelength

We develop a generalized model in order to calculate the point spread functions in both the focal and the detection planes for the electric field strengths. In these calculations, based on the generalized Jones matrices, we introduce all of the interdependent parameters that could influence the spatial resolution of a confocal optical microscope. Our proposed model is more nearly complete, since we make no approximations of the scattered electric fields. These results can be successfully applied to standard confocal optical techniques to get a better understanding for more quantitative interpretations of the probe.

International audience; no abstract

International audience; In thin film polycrystalline CdS/CIGS heterojunction solar cells, understanding the intrinsic and interface defect properties is crucial to optimize their performances. In this paper, we focus our attention on the CdS/CIGS hetero-interface at different stages of its formation. All investigations were carried out on CIGS co-evaporated samples elaborated in pilot-line conditions onto which the CdS layer was deposited by chemical bath deposition (CBD). This latter chemical process involves the use of a NH, solution that modifies the ClGS surface composition. In order to separate the respective role of the NH/sub 3/ bath and the CdS layer thickness , we have investigated samples elaborated with several NH/sub 3/ pretreatment time of CIGS surface prior to CdS deposition. Admittance spectroscopy was used to follow the evolution of the hetero-interface defects properties.

International audience; no abstract

We study, by means of numerical simulation, the impact of doping and traps on the performance of the "solar blind" ultraviolet Schottky detector based on AlGaN. We implemented physical models and AlGaN material properties taken from the literature, or from the interpolation between the binary materials (GaN and AlN) weighted by the mole fractions. We found that doping and traps highly impact the spectral response of the device, and in particular a compromise in the doping concentration must be reached in order to optimize the spectral response of the detector. These results give us a powerful tool to quantitatively understand the impact of elaboration and processing conditions on photodetector characteristics, and thus identify the key issues for the development of the technology.

International audience; The current search of low-cost and more environmentally friendly photovoltaic technologies and is a driving force for the development of thin-film Cu2O as absorber material. Indeed, by combining its earth abundance and potentially excellent electrical and optical properties, cuprous oxide is one of the highest potential metal oxides for the absorber layer of solar cells. Usually, photovoltaics based on bulk cuprous oxide were produced by forming the Cu2O absorber material from thermal oxidation of copper. However, the thermal oxidation method requires high energy consumption, which limits the development of Cu2O based solar cells at low cost and industrial scale. The ultrasonic spray pyrolysis (USP) technique meets these crucial requirements of low cost and compatibility with large area industrial manufacturing. Nevertheless, the deposition of Cu2O thin films by USP still suffers from the novelty of this elaboration process as their lower properties are detrimental to the performances of photovoltaic devices, mainly due to the high concentration of impurities. Very recently, the feasibility of using new precursor solution protocol was suggested by Plankensteiner et al. (ChemNanoMat 6 4 (2020). pp. 663–671) and consists in the substitution of the glucose oxidizer agent by D-sorbitol or glycerol to improve Cu2O thin film properties as this reactant might decrease carbon related by-products during the pyrolysis reaction and thus impurities in the Cu2O thin films. Beyond the feasibility and in order to investigate the Cu2O thin films obtained by USP using D-sorbitol as a new oxidizer agent and to optimize the material for all-oxide solar cell applications, the present work focus on the detailed study of thin film microstructural and optical properties with respect to elaboration conditions, mainly the concentration, pH and thickness, thanks to a specific design of experiment. The deposited thin films properties, using this new precursor solution, were compared to the standard solution processed Cu2O. Cuprous oxide thin films are thus characterized from transmission measurements to investigate the optical properties and evaluate the defects thanks to Urbach energy and absorption edge comparisons. High resolution confocal Raman mapping was used for phase analysis while the microstructure of thin films is analyzed by scanning electron microscopy. Finally, thanks to the correlation between the optical properties, Raman mapping and scanning electron microscopy, the evolution of the microstructure of the thin films with respect to the deposition conditions is presented and allow to better understand Cu2O thin film properties with the aim of enhancing all-oxide photovoltaic performances.

National audience

National audience; Aujourd’hui, la grande majorité des panneaux photovoltaïques fabriqués dans le monde sont à base de silicium. Cependant, ces panneaux souffrent d’un faible rendement de conversion. Afin d’améliorer ce rendement, d’autres matériaux alternatives sont étudiés. Parmi ces nouveaux matériaux, le nitrure d’Indium Gallium (InGaN) possède le potentiel pour réaliser une avancée majeure de l’industrie photovoltaïque. En effet, ces matériaux possèdent des caractéristiques uniques pour réaliser des cellules solaires à très haut rendement de conversion grâce à une bande d’énergie interdite large et modulable juste en changeant la composition d’indium dans le matériaux. L’InGaN possède d’autres avantages, notamment, un coefficient d’absorption très élevé dans toute la gamme du spectre solaire, des mobilités élevées, des masses effectives relativement faibles et une très grande résistance aux rayonnements et autres conditions extrêmes. Cependant, il reste plusieurs difficultés à franchir avant la commercialisation de cellules solaires à base de ce matériau. En effet, InGaN souffre du manque de substrats adaptés pour la croissance épitaxiale, d’une densité de défauts très élevée, et de la difficulté à réaliser le dopage de type-p. L’objectif de notre travail est alors, la modélisation et l’optimisation de différentes structures de cellules solaires à base d’InGaN. La modélisation se fait en utilisant le logiciel ATLAS de SILVACO (Silicon valley Corporation), et l’optimisation se fait en couplant ATLAS avec des outils mathématiques d’optimisation. Nous utilisons pour cela, des algorithmes mathématiques rigoureux de Sage/SciPy (Logiciel open source).Le but est d’optimiser le rendement de la cellule en optimisant simultanément plusieurs paramètres de la cellule solaire (paramètres physiques et géométriques). IL s’agit donc d’une optimisation multivariée qui diffère de l’optimisation paramétrique généralement utilisée.Nous avons donc ici, étudié une nouvelle structure de cellule solaire basée sur un contact Schottky (Contact métal/semi-conducteur) entre une fine couche métallique et le Nitrure de Galium Indium.Nous avons pour cette structure, optimisé le rendement de la cellule en optimisant simultanément plusieurs paramètres de la cellule solaire, ce qui est à notre connaissance une première. Nous avons obtenu un rendement optimal de 18.2%. Ce dernier montre le mérite d’une telle structure qui pourrait être une alternative aux structure PN et PIN afin d’éviter les difficultés liées à la couche P de la cellule solaire.

International audience; All-oxide photovoltaics is a new and very promising technology for low cost and efficient solar cells using earth-abundant and environmentally compatible materials. To match the requirements of this technology, beyond the optimization of the absorber layer, it is crucial to elaborate window and transport layers with excellent optical and structural properties in a wide range of thickness. Among the oxide materials, zinc oxide is a key material for the realization of these layers in the targeted all-oxide solar cells. Beside the low toxicity and abundance of ZnO, the reduction of the environmental footprint of photovoltaic technology could benefit from the low energy and low precursor consumption of the ultrasonic spray pyrolysis (USP) process. In addition to the environmental aspects, the USP process combines many advantages compared to conventional methods such as low-cost and large-scale production capability. The potential for elaboration of thin films of suitable structural and optical properties of this process combined with the previously mentioned advantages makes it of high interest for the future of photovoltaics. To date, the optical and structural properties of ZnO elaborated by USP have not been fully investigated with respect to the precursor solution concentration, which could have a strong impact on these properties and thus on the performances of the solar cell.ZnO thin films were deposited using the USP process after a precise optimization of the main growth conditions, namely the substrate temperature, spray pressure, nozzle speed and precursor solution flux, according to a specific design of experiment. ZnO films were confirmed to be conductive by showing resistivity values in the order of 1 Ω.cm. For this study, we used X-ray diffraction (XRD) and Raman spectroscopy to analyze the crystal structure, orientation and texture coefficient. Our results show that the preferential orientation can be controlled to be either (002) or (100) by adjusting the precursor solution concentration. On the one hand, the precise control of the orientation allows to better control the optical properties, that are crucial in our application, and, on the other hand, limit the defects at the heterointerface. The morphological properties were studied using atomic force microscopy and were correlated to the structural properties of the ZnO thin films. For instance, high consistency was evidenced between the AFM measured grain size and the XRD measured crystallite size. Finally, the optical properties were studied from UV/visible transmittance spectroscopy. The deposited ZnO films exhibit high transmittance above 90 % for the whole concentration range of the precursor solution with a maximum as high as 95 %. The resulting optical and structural properties could benefit to the performances of all-oxide solar cells deposited by USP.

International audience; The synthesis of new efficient low cost solar cells made with earth abundant materials requires on the one hand the development of such materials and, on the other hand, an adequate design of the solar cell that optimizes their use. This latter part is all the more challenging as the materials can be tuned in a variety of ways, adjusting for instance their doping, composition, bandgap and thickness. The high number of parameters that can be adjusted implies that finding their optimal combination is a task in itself, which is presently addressed by a parametic optimisation: optimising one parameter at a time with respect to the cell efficiency, the others being kept constant. Despite its apparent simplicity, this method is time consuming and is not proven mathematically to allow to find the optimal parameter set. Mathematically proven methods can now be easily used in the field of photovoltaics, which allow a simultaneous optimisation of an increased number of parameters, implying a susbtantial decrease in the computation time, along with an increase in the precision of the prediction. A review of present methods and how we have improved them for speed, correctness and precision will be provided.

Chemistry of co-evaporated CIGS surfaces submitted to chemical treatments relevant to fabrication steps were investigated by XPS and admittance spectroscopy. A Se XPS signal specific of the CIGS surfaces was identified. Surface states seen by Admittance and surface chemistry are seen to change significantly during the elaboration steps. Consequences for device elaboration are briefly discussed.

In recent years, Gallium Indium Nitride (InGaN) alloy has become a semiconductor of choice for the realization of optoelectronic devices, because of its wide spectral coverage, with a bandgap that can be modulated, by changing the indium composition, between 0.7 eV and 3.4 eV. This allows the absorption of a large part of the solar spectrumand makes the InGaN alloy an excellent candidate for the realization of high efficiency multi-junction solar cells. This thesis work led to a further investigation into the performance of different InGaN-based solar cell structures. It is part of a project aiming to associate mathematical optimization methods with a rigorous simulation process based as much as possible on models and experimental results. This is a new optimization approach that optimizes the performance of solar cells by simultaneously optimizing several parameters (physical and geometrical) of the solar cell. We have studied for this thesis, different structures of single junction solar cells, including new structures without P layer and we have also studied a complex structure with double junction. These studies allowed us to evaluate the optimal performance that InGaN-based solar cells can achieve for their design and future development; L’alliage de Nitrure de Gallium et d’Indium (InGaN) est devenu au cours des dernières années un semi-conducteur important pour la réalisation de composants optoélectroniques, du fait de sa bande interdite modulable en fonction de la composition d’indium, entre 0.7 eV à 3.4 eV. Ceci permet l’absorption d’une grande partie du spectre solaire et fait de l’alliage InGaN un excellent candidat pour la réalisation de cellules solaires multijonctions à très haut rendement. Ce travail de thèse a permis une investigation approfondie sur les performances de différentes structures de cellules solaire à base d’InGaN. Il s’inscrit dans le cadre d’un projet visant à associer des méthodes d’optimisation mathématique multivariée à une démarche rigoureuse de simulation s’appuyant autant que possible sur des modèles et résultats expérimentaux. Il s’agit d’une nouvelle approche qui permet d’étudier les performances des cellules solaires en optimisant simultanément plusieurs paramètres (physiques et géométriques) de la cellule solaire. Nous avons étudié pour cette thèse, différentes structures de cellules solaires à simple jonction, notamment de nouvelles structures sans couche P et avons fait également l’étude d’une structure complexe à double jonction. Ces études nous ont permis d’évaluer les performances optimales que pourraient avoir les cellules à base d’InGaN et seront importantes pour la conception et l’élaboration future de cellules solaires InGaN à haut rendement

In recent years, Gallium Indium Nitride (InGaN) alloy has become a semiconductor of choice for the realization of optoelectronic devices, because of its wide spectral coverage, with a bandgap that can be modulated, by changing the indium composition, between 0.7 eV and 3.4 eV. This allows the absorption of a large part of the solar spectrumand makes the InGaN alloy an excellent candidate for the realization of high efficiency multi-junction solar cells. This thesis work led to a further investigation into the performance of different InGaN-based solar cell structures. It is part of a project aiming to associate mathematical optimization methods with a rigorous simulation process based as much as possible on models and experimental results. This is a new optimization approach that optimizes the performance of solar cells by simultaneously optimizing several parameters (physical and geometrical) of the solar cell. We have studied for this thesis, different structures of single junction solar cells, including new structures without P layer and we have also studied a complex structure with double junction. These studies allowed us to evaluate the optimal performance that InGaN-based solar cells can achieve for their design and future development, L’alliage de Nitrure de Gallium et d’Indium (InGaN) est devenu au cours des dernières années un semi-conducteur important pour la réalisation de composants optoélectroniques, du fait de sa bande interdite modulable en fonction de la composition d’indium, entre 0.7 eV à 3.4 eV. Ceci permet l’absorption d’une grande partie du spectre solaire et fait de l’alliage InGaN un excellent candidat pour la réalisation de cellules solaires multijonctions à très haut rendement. Ce travail de thèse a permis une investigation approfondie sur les performances de différentes structures de cellules solaire à base d’InGaN. Il s’inscrit dans le cadre d’un projet visant à associer des méthodes d’optimisation mathématique multivariée à une démarche rigoureuse de simulation s’appuyant autant que possible sur des modèles et résultats expérimentaux. Il s’agit d’une nouvelle approche qui permet d’étudier les performances des cellules solaires en optimisant simultanément plusieurs paramètres (physiques et géométriques) de la cellule solaire. Nous avons étudié pour cette thèse, différentes structures de cellules solaires à simple jonction, notamment de nouvelles structures sans couche P et avons fait également l’étude d’une structure complexe à double jonction. Ces études nous ont permis d’évaluer les performances optimales que pourraient avoir les cellules à base d’InGaN et seront importantes pour la conception et l’élaboration future de cellules solaires InGaN à haut rendement