Fully Solution Processed Pure α‐Phase Formamidinium Lead Iodide Perovskite Solar Cells for Scalable Production in Ambient Condition

Manufacturing commercially viable perovskite solar cells still requires appropriate low‐temperature and scalable deposition processes to be developed. While α‐phase FAPbI3 has higher thermal stability and broader absorption than MAPbI3, there still is no report of a pure α‐phase FAPbI3 perovskite film obtained by a scalable printing method. Moreover, spontaneous conversion of the α‐phase to non‐perovskite δ‐phase under ambient conditions poses a serious challenge for practical applications. Herein, a scalable and fully solution based printing method for the fabrication of pure α‐phase FAPbI3 perovskite solar cells is reported. Through adding N‐methyl pyrrolidone and methylammonium chloride to the dimethylformamide based precursor solution to control the crystallization, and vacuum or air‐flow assisted film drying, pure α‐FAPbI3 phase is obtained by doctor blading. The resulting α‐FAPbI3 film is highly stable, with no δ‐FAPbI3 phase being formed even after keeping it in an ambient atmosphere over a period of 200 days without encapsulation. In addition, a fully solution processed PSC with a PCE of 16.1% is processed by the vacuum assisted method, and 17.8% by the air‐flow assisted method. Replacing silver with a printed carbon electrode provides a stable PCE up to 15% for the vacuum assisted and 16.4% for the air‐flow assisted method, which is the highest performance of FAPbI3 solar cells to date. Compared with MAPbI3, the fully printed FAPbI3 perovskite devices exhibit a remarkable thermal stability in humid atmospheres which makes them a promising candidate for scalable production and commercialization.