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This paper aims at providing an updated overview of the main achievements in the development of solar cells based on Cu2ZnSn(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.

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.

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.