Simultaneous cation substitution and rear interface engineering strategies for highly efficient CZTSSe-based solar cells

Abstract

Kesterite-based thin-film solar cells (TFSCs) exhibit limited device performance improvements owing to large open circuit voltage (V_oc)-deficit, which is attributed to the presence of deep-level defect clusters in the bulk material and Sn-ion destabilization at the rear contact. Various strategies have been extensively investigated to address these drawbacks; however, several issues remain unresolved. In this paper, we present a combined double-cation substitution and rear-interface engineering strategy for realizing highly efficient CZTSSe-based TFSCs. The simultaneous use of the above strategies provided a synergetic effect, suppressing the formation of Zn- and Sn-related defects and the corresponding defect clusters. Consequently, it reduced the recombination rate, improved the microstructure with a large grain size and without voids, reduced V_oc-deficit and the band-tailing states, and enhanced device parameters. In particular, the power conversion efficiency increased from 8.28 to 11.23%. This study elucidated the distinct correlation between Zn- and Sn-defects (and/or defect clusters) and various device characteristics, providing valuable insights for improving the performance of kesterite-based TFSCs.