Inorganic Rubidium Cation as an Enhancer for Photovoltaic Performance and Moisture Stability of HC(NH2)2PbI3 Perovskite Solar Cells.

Perovskite solar cells (PSCs) based on organic monovalent cation (methylammonium or formamidinium) have shown excellent optoelectronic properties with high efficiencies above 22%, threatening the status of silicon solar cells. However, critical issues of long-term stability have to be solved for commercialization. The severe weakness of the state-of-the-art PSCs against moisture originates mainly from the hygroscopic organic cations. Here, rubidium (Rb) is suggested as a promising candidate for an inorganic-organic mixed cation system to enhance moisture-tolerance and photovoltaic performances of formamidinium lead iodide (FAPbI₃). Partial incorporation of Rb in FAPbI₃ tunes the tolerance factor and stabilizes the photoactive perovskite structure. Phase conversion from hexagonal yellow FAPbI₃ to trigonal black FAPbI₃ becomes favored when Rb is introduced. The authors find that the absorbance and fluorescence lifetime of 5% Rb-incorporated FAPbI₃ (Rb_0.05FA_0.95PbI₃) are enhanced than bare FAPbI₃. Rb_0.05FA_0.95PbI₃-based PSCs exhibit a best power conversion efficiency of 17.16%, which is much higher than that of the FAPbI₃ device (13.56%). Moreover, it is demonstrated that the Rb_0.05FA_0.95PbI₃ film shows superior stability against high humidity (85%) and the full device made with the mixed perovskite exhibits remarkable long-term stability under ambient condition without encapsulation, retaining the high performance for 1000 h. [ABSTRACT FROM AUTHOR]