Improved performance of double Cs2AgBiBr6 perovskite solar cells by engineering passivation defects with Co2+ additives

Abstract

Cs2AgBiBr6, a double perovskite structure, offers potential as a stable and non-toxic alternative to organic lead perovskites. However, challenges such as poor film quality and a wide indirect band gap have limited its applications. In this study, we introduced Co2+ cations into the precursor solution to slow down Cs2AgBiBr6 film crystallization kinetics. This intervention led to improved film quality, larger grain sizes, reduced defect densities, band gap modulation, and increased solar cell efficiency. Additionally, Co2+ B-site substitution effectively reduced bromine vacancies in the pristine perovskite, mitigating carrier defect recombination. Co2+ also lowered the band gap of Cs2AgBiBr6 and adjusted energy level arrangements, facilitating carrier transport, enhancing electron-hole extraction, and improving conductivity. We investigated the optimal Co2+ addition ratio and elucidated the enhancement mechanisms. The introduction of Co2+ increased power conversion efficiency from 2.11 % to 3.50 % and short-circuit current density from 3.88 to 4.88 mA/cm2. This study offers a straightforward method to enhance Cs2AgBiBr6-based solar cells.