Realization of 11.5% Efficiency Cu2ZnSn(S,Se)4 Thin‐Film Solar Cells by Manipulating the Phase Structure of Precursor Films

Cu 2 ZnSn(S,Se) 4 has been widely regarded as a promising thin‐film solar cell material. In recent years, the development of Cu 2 ZnSn(S,Se) 4 solar cells has encountered a bottleneck, and the higher open‐circuit voltage deficit mainly caused by the secondary phase, CZTSSe/CdS interface recombination, deep‐level defects, and band‐tailing effects has been an outstanding issue. Herein, the influence of the composition and phase distribution of the precursor thin film on the defect and performance of Cu 2 ZnSn(S,Se) 4 solar cells is studied. By modifying the distribution of composition and phase for precursor films, a Cu 2 ZnSn(S,Se) 4 absorber layer without secondary phase and with fewer detrimental defects can be obtained from the pure‐phase precursor film. Thanks to the reduction of the band‐tailing effects, the increase in the depletion width for heterojunction, and the decrease in CZTSSe/CdS interface recombination, the photovoltaic performance of CZTSSe thin‐film solar cells is significantly improved. Finally, based on the excellent kesterite absorber layer, a Cu 2 ZnSn(S,Se) 4 solar cell with 11.51% power conversion efficiency (the active area efficiency is 12.4%) is prepared.