Compositional and Interfacial Modification of Cu2ZnSn(S,Se)4 Thin‐Film Solar Cells Prepared by Electrochemical Deposition

Abstract A highly efficient Cu 2 ZnSn(S,Se) 4 (CZTSSe)‐based thin‐film solar cell (9.9 %) was prepared using an electrochemical deposition method followed by thermal annealing. The Cu–Zn–Sn alloy films was grown on a Mo‐coated glass substrate using a one‐pot electrochemical deposition process, and the metallic precursor films was annealed under a mixed atmosphere of S and Se to form CZTSSe thin films with bandgap energies ranging from 1.0 to 1.2 eV. The compositional modification of the S/(S+Se) ratio shows a trade‐off effect between the photocurrent and photovoltage, resulting in an optimum bandgap of roughly 1.14 eV. In addition, the increased S content near the p–n junction reduces the dark current and interface recombination, resulting in a further enhancement of the open‐circuit voltage. As a result of the compositional and interfacial modification, the best CZTSSe‐based thin‐film solar cell exhibits a conversion efficiency of 9.9 %, which is among the highest efficiencies reported so far for electrochemically deposited CZTSSe‐based thin‐film solar cells.