Because of remarkable properties of InGaN, we simulated and optimized an InGaN-based dual-junction solar cell connected by a specifically designed tunnel junction. The device is simulated in the framework of a drift-diffusion model using the ATLAS device simulation framework from the Silvaco company. The optimization is done by coupling ATLAS with multivariate mathematical optimization methods based on state-of-the-art optimization algorithms. For that, we used a Python package that we developed in the SAGE software interface. The objective is to optimize the conversion efficiency of the solar cell by simultaneously optimizing several physical and geometrical parameters of the solar cell. It is an unprecedented multivariate optimization for solar cells which takes into account the correlation between these parameters. For this solar cell, we optimized simultaneously 11 parameters of the structure. An optimum conversion efficiency of 24% was predicted for this designed solar cell.

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.

Choosing the Indium Gallium Nitride (InGaN) ternary alloy for thin films solar cells might yield high benefits concerning efficiency and reliability, because its bandgap can be tuned through the Indium composition and radiations have little destructive effect on it. It may also reveal challenges because good quality p-doped InGaN layers are difficult to elaborate. In this letter, a new design for an InGaN thin film solar cell is optimized, where the player of a PIN structure is replaced by a Schottky contact, leading to a Metal-IN (MIN) structure. With a simulated efficiency of 19.8%, the MIN structure performs better than the previously studied Schottky structure, while increasing its fabrication tolerance and thus functional reliability a. Owing to its good tolerance to radiations [1], its high light absorption [2, 3] and its Indium–composition–tuned bandgap [4, 5], 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 [6], the lack of dedicated ac-ceptors [7] and the complex fabrication process itself [8, 9]. To these drawbacks can be added the uneasy fabrication of ohmic contacts [4] and the difficulty to grow the high-quality-high-Indium-content thin films [10] 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 [11]. In this letter, is proposed a new Metal-IN (MIN) InGaN solar cell structure 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 [12].

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.

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.

L'alliage de Nitrure de Gallium et d'Indium (InGaN) est un matériau semi-conducteur qui présente aujourd’hui un grand intérêt pour la réalisation de cellules solaires à très haut rendement grâce à sa large et modulable bande interdite en fonction de la composition d’Indium. Néanmoins, la croissance de couches épitaxiales d’InGaN, le dopage et le contact ohmique au niveau de la couche “P” reste un challenge. La cellule solaire Schottky est une bonne alternative pour éviter la couche “P”. Nous avons simulé et optimisé, avec des méthodes mathématiques rigoureuses, une cellule solaire Schottky afin de trouver les paramètres géométriques et physiques optimaux donnant ainsi le rendement optimal de la cellule solaire. 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.

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.

The development of new thin films solar cells is highly accelerated by using rigorous optimization approach. A large set of parameters is involved in the solar cell operation: active layer thickness, composition, bandgap, doping, contacts, etc. The study of the solar cell performances with respect to these linked parameters is necessary to better understand the underlying physics and to optimize the final device. We propose in this poster presentation (*) a new open-source solar cell optimizer: SLALOM for SoLAr ceLl multivariate OptiMizer. SLALOM implements, for the first time for solar cells, a rigorous multivariate approach while the standard optimization work used to use the one-by-one parameter procedure. SLALOM is implemented to be easily extended to any simulator, the core code itself does not depend on any particular engine. It can be adapted for any solar cell structure, runs locally or remotely on a calculation server, using the SSH protocol and includes a graphical user interface to real-time monitor the optimization. Two study cases, InGaN and CZTS solar cells, are presented to show the SLALOM ability to become a useful tool for the development of novel solar cells.

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The design and optimization of novel structures is an essential part of the next-generation solar cells development. Indeed, the technological steps involved in the development of high-performance solar cells involve a huge set of interdependent physical and geometrical parameters: layers thicknesses, dopings, compositions, and defect characteristics. In this work, we propose a new open-source and free solar cell optimizer: SLALOM À for SoLAr ceLl multivariate OptiMizer À that implements a rigorous multivariate approach, which improves from the one-parameter-at-a-time procedure that is traditionally used in the field to a state-of-the-art multivariate approach. Applied to indium gallium nitride (InGaN) solar cells, it shows its potential to become a useful tool for the development of novel solar cells. SLALOM is implemented to be extended to any semiconductor simulation engine. Several models for solar cells have been implemented in SLALOM, including, for instance, InGaN. One can adapt these models to any solar cell technology by changing the parameter set, the here proposed generic code structure remaining unchanged.