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

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 ap-plications. 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 den-sities, 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.