Nonstoichiometric acid-base reaction as reliable synthetic route to highly stable CH 3 NH 3 PbI 3 perovskite film

Perovskite solar cells have received worldwide interests due to swiftly improved efficiency but the poor stability of the perovskite component hampers the device fabrication under normal condition. Herein, we develop a reliable nonstoichiometric acid-base reaction route to stable perovskite films by intermediate chemistry and technology. Perovskite thin-film prepared by nonstoichiometric acid-base reaction route is stable for two months with negligible PbI 2 -impurity under 1/465% humidity, whereas other perovskites prepared by traditional methods degrade distinctly after 2 weeks. Route optimization involves the reaction of PbI 2 with excess HI to generate HPbI 3, which subsequently undergoes reaction with excess CH 3 NH 2 to deliver CH 3 NH 3 PbI 3 thin films. High quality of intermediate HPbI 3 and CH 3 NH 2 abundance are two important factors to stable CH 3 NH 3 PbI 3 perovskite. Excess volatile acid/base not only affords full conversion in nonstoichiometric acid-base reaction route but also permits its facile removal for stoichiometric purification, resulting in average efficiency of 16.1% in forward/reverse scans.