Additive-assisted defect passivation of perovskite with metformin hydrochloride: toward high-performance p-i-n perovskite solar cells

Defects at the grain boundaries and surfaces of perovskite thin films are the key factors that cause nonradiative recombination, thus restricting the performance of perovskite solar cells (Pero-SCs). By introducing foreign additives to manage the chemical environment of the precursor, perovskite films can obtain optimized morphology and reduced defects, thereby enhancing the photovoltaic performance and stability of derived Pero-SCs. Herein, we report the bifunctional molecule metformin hydrochloride (MetHCl), whose multidentate structure is capable of simultaneously passivating several sorts of defects in perovskite films. Concurrently, the strong binding ability to Pb2+ makes it impressive in regulating perovskite crystallization. The nonvolatile MetHCl can remain in the perovskite film, contributing to acquiring a high-quality film with denser grains and fewer pinholes. Finally, p-i-n Pero-SCs containing the MetHCl additive exhibited enhanced stability and achieved a champion power conversion efficiency of 21.59% with an open-circuit voltage of 1.17 V.