Physical routes for the synthesis of kesterite

This paper provides an overview of the physical vapor technologies used to synthesize Cu2ZnSn(S,Se)4 thin films as absorber layers for photovoltaic applications. Through the years, CZT(S,Se) thin films have been fabricated using sequential stacking or co-sputtering of precursors as well as using sequential or co-evaporation of elemental sources, leading to high-efficient solar cells. In addition, pulsed laser deposition of composite targets and monograin growth by the molten salt method were developed as alternative methods for kesterite layers deposition. This review presents the growing increase of the kesterite-based solar cell efficiencies achieved over the recent years. A historical description of the main issues limiting this efficiency and of the experimental pathways designed to prevent or limit these issues is provided and discussed as well. Afinal section is dedicated to the description of promising process steps aiming at further improvements of solar cell efficiency, such as alkali doping and bandgap grading1. R Caballero and M León acknowledge financial support via the Spanish Ministry of Science, Innovation and Universities project (WINCOST, ENE2016-80788-C5-2-R) and thank H2020 EU Programme under the project INFINITE-CELL (H2020-MSCA-RISE-2017-777968). 2. S Canulescu and J Schou acknowledge the support from Innovation Fund Denmark. 3. D-H Kim acknowledges financial support via the DGIST R&D Program of the Ministry of Science and ICT, KOREA (18-BD-05). 4.C. Malerba acknowledges the support from the Italian Ministry of Economic development in the framework of the Operating Agreement with ENEA for the Research on the Electric System. 5.A Redinger acknowledges financial support via the FNR Attract program, Project : SUNSPOT, Nr.11244141. 6. E Saucedo thanks H2020 EU Programme under the projects STARCELL (H2020-NMBP-03-2016-720907) and INFINITE-CELL (H2020-MSCA-RISE-2017-777968), the Spanish Ministry of Science, Innovation and Universities for the IGNITE project (ENE2017-87671-C3-1-R), and the European Regional Development Funds (ERDF, FEDER Programa Competitivitat de Catalunya 2007–2013). IREC belong to the SEMS (Solar Energy Materials and Systems) Consolidated Research Group of the ‘Generalitat de Catalunya’ (Ref. 2017 SGR 862). 7. Taltech acknowledges financial support via the Estonian Ministry of Education and Research funding project IUT19-28 and the European Union Regional Development Fund, Project TK141. 8. B Vermang has received funding from the European Research Council (ERC) under the European Union’s Horizon 2020 Research and Innovation Programme (Grant Agreement No 715027

Low temperature time resolved photoluminescence in ordered and disordered Cu2ZnSnS4 single crystals

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History and prospects of the physical synthesis of kesterite for photovoltaic applications

Through the years, kesterite Cu2ZnSn(S,Se)4 thin films have been fabricated using various physical synthesis technologies. Among them, sequential stacking or co-sputtering of precursors as well as sequential or co- evaporation of elemental sources have led to the achievement of high-efficient solar cells. In this work, we provide an up-to-date overview of the physical vapor technologies used to synthesize CZT(S,Se) thin films as absorber layers for photovoltaic applications. This review starts with an enumeration of the well-known pro- cesses used for the growth of CZT(S,Se) absorber layers. A historical description of the main issues limiting the efficiency and of the experimental pathways designed to prevent or limit these issues is presented and discussed. The discussion is articulated through the transition from a one-step synthesis process consisting in a high temperature deposition to a two-step synthesis process composed of (i) the deposition of a precursor film and (ii) a thermal annealing under S (sulfurization) or Se (selenization) atmosphere. To complete the de- scription, morphological properties, such as void formation and thin films blistering are discussed in relation with the synthesis protocols used. In addition, alternative methods for kesterite layers deposition are devel- oped such as pulsed laser deposition of composite targets and monograin growth by the molten salt method, both leading to a significant progress in device efficiency. A final discussion is dedicated to the description of promising process steps aiming at further improvements of solar cell efficiencies, such as alkali doping and alloying of kesterite for bandgap grading. As a result, this work highlights the growing increase of the kesterite-based solar cell efficiencies achieved over the recent years and offers a broad and updated overview of the physical vapor deposition technologies currently applied to the fabrication of performant CZT(S,Se) absorber layers