Optimization of α-FAPbI 3 crystallization by intermediate compounds transformation for efficient and stable perovskite solar cells

Efficient and stable perovskite solar cells (PSCs) is inseparable from the deposition of splendid perovskite absorbent layer. The intermediate compounds of (PbI2)2RbAc was constructed through the introduction of RbAc additive in the PbI2 precursor solution, and further transformed into the (PbI2)2RbCl secondary phase under the annealing of perovskite films, along with delaying the growth of perovskite crystals, regulating residual PbI2, and optimizing the quality of perovskite crystals. Besides, the introduction of RbAc additive passivated the defects of alpha-FAPbI3 perovskite and inhibited the non-radiative recombination of carriers. Based on the novel mechanism of regulating alpha-FAPbI3 crystallization through secondary phase transformation, PSCs optimized with RbAc additive achieved a power conversion efficiency (PCE) of 24.45%, and the PSCs prepared under natural humid air environment obtained a PCE of 23.20%. Moreover, the optimized PSCs retained 91.55% of the initial PCE after 1200 h of storage, and showed excellent light and thermal stability.