Adopting a functional programming style could make your programs more robust, more compact, and more easily parallelizable. However, mastering it requires some effort. This article's purpose is to explain what functional programming is and how it differs from traditional imperative programming. The author also explains how functional programming helps with concurrent and parallel programming. The language I use in the examples is Clojure, a modern dialect of Lisp.

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.

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.

A detailed investigation on the performance of an InGaN-based double-junction solar cell was carried out. We have globally simulated the solar cell using empirical InGaN material parameters, to avoid any overestimation in the solar cell performances. In order to take into account the interdependence of the solar cell physical and geometrical parameters, ensuring the absoluteness of the optimized photovoltaic performances, the cell was optimized using a multivariate optimization algorithm that simultaneously optimizes eleven physical and geometrical parameters. We obtained an optimal efficiency of 24.4%, with a short circuit current J SC = 12.92 mA=cm 2 , an open circuit voltage V OC = 2.287 V and a fill factor FF = 82.55%. We then quantitatively investigated the impact on the solar cell performances of the internal polarization and structural defects in InGaN. We have shown that the internal polarization reduces the performance of the cell by inducing an electric field which does not favor an efficient collection of photo-generated carriers. We have also investigated the impact of structural defects in InGaN, including disorder and deep defects, and correlated their effect to the InGaN doping concentration.

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.

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.

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.

The InGaN ternary alloy has the potentiality to achieve high efficiency solar cells: tunable bandgap in the whole solar spectrum, high absorption coefficient, high stability and radiation tolerance. These very promising characteristics make InGaN potentially ideal for designing and developing next-generation high-efficiency thin films solar cells. However, challenging issues remain to address: (i) the difficulty to elaborate sufficiently thick monocrystalline InGaN layers with a high Indium content; (a) the high defects density and the spontaneous and piezoelectric polarizations; (iii) the p-doping which remains difficult to master. In this report, we use rigorous optimization approach based on state-of-the-art optimization algorithms to investigate the effect of defects and polarization (spontaneous and piezoelectric) on a double junction InGaN solar cell. A better understanding of the mechanisms involved in the heterostructure has a crucial impact on the design and elaboration of high efficiency InGaN thin films solar cells which require, in particular, a precise control of the Tunnel Junction elaboration which is still very challenging.

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.