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We review the stability and reliability results of kesterite (Cu2ZnSn(S,Se)4, CZTSSe)-based solar cells and we complete the reviewed data with additional as yet unpublished data on these matters. We also review published and new data on upscaling and the possible technological applications for this material. Kesterite material is composed of mainly earth-abundant elements and is therefore very attractive for large-scale applications. Stability data are so far quite scarce and the main results are the accelerated aging tests carried out for CZTSSe monograin technology, as well as yet unpublished data on long indoor and outdoor irradiance tests carried out on thin-film CZTSSe technology deposited by a wet processing method. On upscaling and technological applications we point out the works on three main large-scale photovoltaic technologies (monograin, in-line vacuum thin film, and wet-deposited thin film), as well as some work on water-splitting applications. ; IMRA Europe and crystalsol thank their numerous co-workers for contributing to this work. The work carried out at cyrstalsol was partly supported by the European Union through the European Regional Development Fund and Archimedes/DoRa project TK141. IMRA Europe, Midsummer and Ayesa acknowledge the European Commision for the funding of the kesterite research from 2017 by the H2020 program under the project STARCELL (H2020-NMBP-03-2016-720907).

CZTS / CdS / ZnO / ITO solar cell was studied using Solar Cell Capacitance Simulato-1D (SCAPS-1D) program. We performed an improvement on the theoretical cell by increasing the doping and thickness of some layers. As a result, the efficiency was shifted from 2.18% to 6.17% and several back reflection layers (BSL) were introduced on the enhanced cell until. We obtained a highest conversion efficiency of 13.99%. The best reflection layer (CZTSSe) was combined with the best buffer layer (CdSe), with thickness of 0.9µm, on the enhanced cell. Thereby, we obtained a cell with a conversion efficiency of 16.53%. A second improvement was made to the best obtained cell, where the CZTSSe with thickness of 0.05µm and the CdSe with thickness of 0.9µm were combined. Consequently, the efficiency was increased from 16.53% to 21.76%. By comparing the experimental results with those obtained with the program, it was found that the program simulates reality, i.e. the experimental and theoretical results matched.

Kesterite solar cells based on Cu2ZnSnS4 and Cu2ZnSnS4 (CZTSe) are potential future candidates to be used in thin-film solar cells. The technology still has to he developed to a great extent and for this to happen, high levels of confidence in the characterization methods are required, so that improvements can he made on solid interpretations. In this study, we show that the interpretations of one of the most used characterization techniques in kesterites, scanning transmission electron microscopy (STEM), might be affected by its specimen preparation when using focused ion beam (FIB). Using complementary measurements based on scanning electron microscopy and Raman scattering spectroscopy, compelling evidence shows that secondary phases of ZnSe mixed in the bulk of CZTSe are the likely cause of the appearance of voids in STEM lamellae. Sputtering simulations support this interpretation by showing that Zn in a ZnSe matrix is preferentially sputtered compared with any metal atom in a CZTSe matrix. ; This work was supported in part by the FEDER funds through the COMPETE 2020 Programme, in part by FCT-Portuguese Foundation for Science and Technology under Project UID/CTM/50025/2013, in part by CAPES (CAPES-INL 04/14), in part by FAPEMIG, and in part by CNPq Brazilian agencies. The work of B. Vermang was supported by the European Research Council under the European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement 715027. The work of P. M. P. Salome was supported in part by the Fundacao para Ciencia e Tecnologia (FCT) under Project IF/00133/2015 and in part by the NovaCell-Development of Novel Ultrathin Solar Cell Architectures for Low-Light, Low-Cost, and Flexible Opto-Electronic Devices Project (028075) co-funded by FCT and the ERDF under Grant COMPETE2020.