Abstract: Organic-inorganic halide perovskites have significant potential for application in next-generation solar cells. However, their applications are limited by challenges associated with large-area processability and long-term stability owing to the presence of pinholes and defect sites. Here, we incorporated cesium formate in a perovskite active layer using a sequential perovskite fabrication process to eliminate the defect sites of perovskites and improve the film processability via roll-to-roll (R2R) processing. The addition of cesium formate salt to the PbI₂ layer influences the perovskite crystal formation behavior as well as increases the perovskite crystallinity and decreases the defect density. Furthermore, cesium formate addition eliminated small PbI₂ grains and smoothed the perovskite surface, resulting in a large crystal grain size. The formate ions interact with the PbI₂ component and passivate halide vacancy defects, reducing nonradiative recombination and improving charge transfer. Additionally, the treated perovskite films were highly stable in air, exhibiting improved efficiency retention over time and achieving a power conversion efficiency (PCE) of > 22% compared to the control. Furthermore, the additive-treated perovskite film was processed using the R2R method, achieving a high PCE of >14% with minimal hysteresis.

Key words: Perovskite Solar Cells, Pseudo-halide ion, Stability, Roll-to-roll process