Concerted Ion Migration and Diffusion‐Induced Degradation in Lead‐Free Ag ₃ BiI ₆ Rudorffite Solar Cells under Ambient Conditions

Silver bismuth iodide (SBI) materials have recently gained attention as nontoxic alternatives to lead perovskites. Although most of the studies been focusing on photovoltaic performance, inherent ionic nature SBI materials, their diffusive behavior, and influence material/device stability is underexplored. Herein, AgBi2I7, Ag2BiI5, Ag3BiI6 thin films are developed in controlled ambient humidity conditions with a decent efficiency up 2.32%. While exploring device stability, it found that exhibits unique ion-migration behavior where Ag+, Bi3+, I− ions migrate diffuse through dopant-free hole transport layer (HTL) leading degradation. Interestingly, this relatively fast for case antisolvent-processed thin-film-based devices contrasting without antisolvent not observed other material-based devices. Theoretical calculations suggest low decomposition enthalpy favors AgI BiI3 causing migration electrode which protected by using thick HTL . The new mechanism reported herein underlines importance material composition fundamental understanding better solar cell design also extending applications various optoelectronics.