Complex Additive?Assisted Crystal Growth and Phase Stabilization of ??FAPbI ₃ Film for Highly Efficient, Air?Stable Perovskite Photovoltaics

Solution-processed formamidinium lead iodide (FAPbI3) perovskite is entropically metastable, and it exhibits condition-induced crystal polymorphism. Under an ambient atmosphere, the photoactive black ?-FAPbI3 converts easily to photoinactive yellow ?-FAPbI3. This ? ? ? phase degradation further accelerated upon exposure high temperature/humidity, directly threatening performance stability of solar cells (PSCs). Herein, cesium iodide-lead iodide:dimethyl sulfoxide (CsI-PbI2:DMSO) complex introduced as a stabilizer modulate crystallization from ?-FAPbI3 precursor simultaneously, serve defect passivator suppress trap states formation. Theoretical simulations experimental results reveal pivotal role additive in optimizing energy band alignment optoelectronic properties most importantly, hindering transition. The best PSC device based on additive-engineered film achieves efficiency ?21.9%, which ?11% higher than that its pristine counterpart (?19.8%). In addition, incorporation CsI-PbI2:DMSO remarkably enhances long-term photostability PSCs by inhibiting ion migrations preserving ?-phase FAPbI3 perovskite. engineering presented herein offers route produce FAPbI3-based with improved performance, stability, reproducibility.