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

Cu₂ZnSn(S,Se)₄ has been widely regarded as a promising thin-film solar cell material. In recent years, the development of Cu₂ZnSn(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 Cu₂ZnSn(S,Se)₄ solar cells is studied. By modifying the distribution of composition and phase for precursor films, a Cu₂ZnSn(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 Cu₂ZnSn(S,Se)₄ solar cell with 11.51% power conversion efficiency (the active area efficiency is 12.4%) is prepared.