Electronic structure and stability of the (0 0 1) surface of halide double perovskite Cs2AgBiBr6

Abstract

Cs2AgBiBr6 is an attractive lead-free candidate for photovoltaic applications. Recently, surfaces were reported to be crucial in improving the power conversion efficiency of Cs2AgBiBr6-based perovskite solar cells (PSCs). However, the in-depth understanding of the stability and electronic structure of Cs2AgBiBr6 surfaces is still lacking. To address it, we explore the energetics and electronic properties of the Cs2AgBiBr6 (001) surface with CsBr and AgBiBr4 terminations by first-principles calculations. It is found that both terminations may coexist on the (001) surface. Importantly, a lack of deep-states assisted carrier recombination and the low probability of the band-edges related nonradiative recombination for the (001) surface may contribute to the long lifetime of carriers observed in Cs2AgBiBr6. Besides, the moderate carrier effective masses of the (001) surface explain the experimental moderate charge-carriers mobility of Cs2AgBiBr6. Encouragingly, there is a considerable difference in ionization potentials for the two terminations, implying that surface/interface engineering can modify the band offset between the light absorber and carrier transporter and shows the potential to improve charge transfer. Our research provides valuable insights into the photoelectric properties of the Cs2AgBiBr6 (001) surface. It is vital for the future design of Cs2AgBiBr6 PSCs through surface/interface engineering.