Modulated crystallization and enhanced stable of high efficient perovskite solar cells with Pb(Ac)2

α-Formamidinium lead iodide (α-FAPbI3) has become one of the most promising candidate materials for stable perovskite solar cells (PSCs) owing to their outstanding optoelectronic properties and high thermal stability. The crystallinity of the active layer of perovskite is essential to the performance of perovskite solar cells. In this paper, we added lead acetate Pb(Ac)2 as a grain growth agent into the perovskite precursor solution to prepare high-efficiency and stable perovskite solar cells. It was revealed that the crystals of Pb(Ac)2-modified film grew selectively along the [200] direction and that the FAPbI3 active layer grains were arranged neatly and densely, due to the significant influence of a moderate amount of weakly acidic Ac- on the crystal growth of FAPbI3. The relative reduction in its grain boundaries led to the decrease in the grain boundary impedance, and it was easier for electrons to perform long-range migration in the perovskite active layer. The beneficial effects of Pb(Ac)2 were further expiored by femtosecond Fs-TA measurements and density of states (tDOS) analysis, where the carrier lifetimes τ2 was increased from 482.4 ps to 1340 ps, and the trap density of film states was significantly reduced. The filling factor (FF) and power conversion efficiency (PCE) were increased from 76.5% and 19.7–81.1% and 21.8%, respectively, the Pb(Ac)2 devices were placed in air for 800 h for the light aging test, and the test results still maintained 90% of the original efficiency, which improved the stability of FAPbI3 crystals.