In Situ erovskitoid Engineering at SnO2 Interface toward Highly Efficient and Stable Formamidinium Lead Triiodide Perovskite Solar Cells

The black-phase formamidinium lead triiodide (alpha-FAPbI(3)) perovskite has turned out to be one of the most efficient light harvesting materials. However, the phase stability of FAPbI(3) is a long-standing issue. Herein, we introduce a layer of tetrabutylammonium fluoride (TBAF) on SnO2, which would form an in situ layer of TBAPbI(3) perovskitoid at the SnO2/FAPbI(3) interface by interacting with PbI2. The results show that this strategy could improve the conductivity of SnO2, passivate the defects in perovskite, improve the phase stability of alpha-FAPbI(3), and retard the nonradiative recombination in the device. As a result, we obtain a champion device with a power conversion efficiency of 23.1% under AM 1.5 G illumination of 100 mW/cm(2). The unencapsulated devices can maintain excellent stability under illumination, thermal stress, and humidity conditions, respectively.