Ambient air-processed Cu2ZnSn(S,Se)4 solar cells with over 12％ efficiency

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) thin films are attractive due to environmental-friendly and earth-abundant constituents, and superior optoelectronic properties such as high absorption coefficient and tunable bandgaps (1.0-1.5 eV).In the past several years,profound progress has been made in CZTSSe via addressing the issues of massive deep defects [1,2], severe band tailing [3], uncontrollable grain growth [4,5], and unoptimized interfaces [6,7].The highest certified power conversion efficiency (PCE) for CZTSSe thin-film solar cells was 12.62％ (the year 2019) from a vacuum-based method [8] and 12.6％ (the year 2014) from a nonvacuum-based method (Table 1) [9].The vacuum-based methods,such as sputtering and evaporation approaches, usually suffer from relatively low throughput and material utilization, and high intrinsic costs.For the non-vacuum-based methods, the highest PCE of 12.6％ was achieved from a spin-coating approach with the hydrazine solution in the glove box [12].Hydrazine is highly toxic and explosive, which hinders the practical application of this approach.For solar cells based on other non-vacuum-based approaches, like electrodeposition and spray pyrolysis, the efficiency is stuck at around 10％.