Effect of Sb–Bi alloying on electron–hole recombination time of Cs2AgBiBr6 double perovskite

Abstract

The double perovskite material Cs₂AgBiBr₆, characterized by high stability, low toxicity, and excellent optoelectronic properties, has emerged as a promising alternative to lead-based halide perovskites in photovoltaic applications. However, its photovoltaic conversion efficiency after integration into solar cell devices is less than 3%, significantly lower than that of traditional perovskite solar cells. While alloying methods have been widely applied in the design of photovoltaic materials, their specific role in modulating the lifetime of photo-generated charge carriers in double-perovskite solar cells remains inadequately explored. In this study, through nonadiabatic molecular dynamics (NAMD) simulations, the excited-state dynamics properties of Cs₂AgBiBr₆ and alloyed Cs₂AgSb_0.375Bi_0.625Br₆ samples were compared. The results revealed that the introduction of Sb ions into the double perovskite structure induces lattice deformation upon heating to 300 K, leading to distortion of Bi–Br bonds and enhanced valence band delocalization. Using the decoherence-induced surface hopping method, the capture and recombination processes of charge carriers between different states were simulated. It was suggested that hole lifetime serves as the primary limiting factor for carrier lifetime in Cs₂AgBiBr₆, and replacing 0.375 proportion of Bi with Sb can decelerate the hole capture rate, extending carrier lifetime by 3–4 times. This study demonstrates that alloying offers a viable approach to optimizing the optoelectronic performance of the Cs₂AgBiBr₆ perovskite, thereby advancing the application of double perovskite materials in the field of photovoltaics.