This paper aims at providing an updated overview of the main achievements in the development of solar cells based on Cu 2 ZnSn(S,Se) 4 (CZTS(Se)) Kesterite absorbers obtained by electrodeposition. Although undoubtedly challenging, the ultimate goal is to learn from the past works and build a solid framework for future advances in this field. What is the reason for the lower efficiency of electrodeposited CZTS(Se)-based devices (8%) compared to the world record efficiency achieved with a hydrazine-based solution approach (12.6%)? Can this gap be filled, or there are intrinsic limitations for this achievement? The review is divided into the three main electrodeposition approaches: sequential elemental layer, alloy co-deposition, and chalcogenide co-deposition. It is argued that considerable technical challenges must be overcome for the latter approach to be successfully applied.Plot of the record power conversion efficiencies of Kesterite sulfide-based solar cells obtained by electrodeposition (hollow dots), and world record efficiency of CZTS(Se)-based devices (full dots). The dashed line shows the 15% minimum efficiency threshold considered relevant for potential industrial application.

International audienceCu2ZnSnSe4 solar cell absorbers are synthesized by large-area electrodeposition of metal stack precursors followed by selenization. A champion solar cell exhibits 8.2% power conversion efficiency, a new record for Cu2ZnSnSe4 solar cells prepared from electrodeposited metallic precursors. Significant improvements of device performance are achieved by the application of two etching procedures and buffer layer optimization. These results validate electrodeposition as a credible alternative to vacuum processes (sputtering, co-evaporation) for earth-abundant thin-film solar cell fabrication at low cost. Copyright (C) 2015 John Wiley & Sons, Ltd

Understanding the impact of GaN surface treatment conditions on dielectric/GaN interface chemical properties is critically important for device performance. This point is under intensive research for the dielectric/GaN structure because GaN does not have a good native oxide quality such as SiO2 used in silicon technologies. The effects of different wet treatments prior to atomic layer deposition (ALD) of thin Al2O3 on Ga-polar GaN were studied by X-ray photoelectron spectroscopy (XPS). The same wet treatments have been applied to the recessed region of AlGaN/GaN heterostructures, followed by ALD of 30 nm Al2O3 in order to form MOS-channel high-electron-mobility transistors (MOSc-HEMTs) on 200 mm GaN-on-Si wafers with CMOS compatible processing. The resulting transistors exhibited a normally off behavior (threshold voltage V TH = 0.4–0.6 V) and their V TH was correlated to the oxidation at the Al2O3/GaN interface, suggesting the presence of donor defects.

This paper presents a simple and nondestructive method to determine doping densities and built-in potential of subcells by adapting the well-known capacitance-voltage (C-V) technique to two-terminal (2 T) tandem solar cells. Because of the electrical coupling between the two subcells in a monolithic 2 T tandem solar cell, the standard method using a Mott-Schottky plot (1/C 2 vs V) cannot be applied. Using numerical modeling, it is demonstrated that, by under chosen illumination conditions where only one subcell can absorb the light, it is possible to explore the bias dependence of the capacitance and to extract the parameters of the other subcell if the appropriate frequency conditions are present. This method is experimentally applied to an AlGaAs/Si tandem cell, and parameters of both AlGaAs and Si cells are extracted.Finally, the validity of that method is assessed by the very good agreement obtained when comparing the values extracted from our measurements on the tandem cell to those extracted from measurements on isotype cells and to the values targeted during the fabrication process of the AlGaAs/Si tandem solar cell.

Cu2ZnSnSe4 solar cells were synthesized by electrodeposition of metal stack precursors followed by selenization, a high potential process for industry, leading to conversion efficiencies above 5%. An additional selenium‐capping layer deposited on the precursor before annealing showed improved uniformity and morphology of CZTSe layers compared to other selenization routes. Two different atmospheric annealing systems were used: a closed graphite box in a tubular furnace and a three‐chamber dynamic rapid thermal processing furnace. The RTP system gave larger grains and more compact layers, whereas CZTSe selenized in tube furnace had smaller grains and a higher series resistance. Both annealing systems gave best cells power conversion efficiencies over 5%. We will discuss the device photoelectric properties and their relation to material structures and processing.

Electrodeposition followed by rapid thermal annealing is a favorable process for industrial solar thin film fabrication. In this regard, we attempt to develop a process for earth‐abundant pure sulfide kesterite solar cells fabrication of Cu2ZnSnS4 (CZTS) at pre‐industrial scale (15 × 15 cm2). Synthesis at a large scale is a challenging issue that we attempt to address discussing the choice of annealing parameters. We found out that in our system a low background pressure is needed to ensure a good vapors distribution. However, S, SnS, Zn volatilities are enhanced, making difficult the control of the composition. Annealing temperature profile has a strong influence on the final absorber composition. The introduction of an intermediate reactive pre‐alloying step previously to the high temperature annealing is shown to help to obtain more compact absorbers, leading to a maximum power conversion efficiency of 2.4% for a 0.435 cm2 CZTS device.

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Monolithic two-terminal III-V on Si dual-junction solar cells, designed for low concentration applications, were fabricated by means of surface-activated direct wafer bonding. The III-V top cell is a heterojunction formed by an n-Ga 0.5 In 0.5 P emitter and a p-Al 0.2 Ga 0.8 As base. An efficiency of 21.1 ± 1.5% at one sun and 23.7 ± 1.7% at 10 suns is demonstrated, which to our knowledge is the best dual-junction twoterminal III-V on Si tandem cell efficiency reported to date under verified reference conditions. The I-V characterization of these 1-cm 2 tandem cells under concentration required the development of a new method using a single-source multiflash solar simulator and not perfectly matched component cells, also known as pseudoisotypes, formed by Si single-junction cells and optical filters. In addition, the spectrum of the pulsed solar simulator was measured using a high-speed CMOS spectrometer, allowing the calculation of the spectral mismatch correction factor. Merging these two techniques results in the hybrid corrected pseudo-isotype (HCPI) characterization method, which shows a fast and accurate performance with a simplified procedure based on a single-source solar simulator. Pseudo-isotypes are easily adaptable to new cell designs by simply using a different filter, hence allowing the characterization of new multijunction solar cell architectures.