Controlled Growth of Large Grains in CH3NH3PbI3 Perovskite Films Mediated by an Intermediate Liquid Phase without an Antisolvent for Efficient Solar Cells

High-quality crystalline large grains with uniform morphologies of the perovskite films are particularly important for achieving stable, high-performance perovskite solar cells. Herein, an effective strategy to control the growth of large grains in the CH 3 NH 3 PbI 3 perovskite films is demonstrated by modifying the perovskite film deposition process through forming an intermediate CH 3 NH 3 PbI 3 ·methylammonium chloride (MACl)· x CH 3 NH 2 liquid phase induced by CH 3 NH 2 gas treatment in combination with a MACl additive without an antisolvent. By tuning the incorporation of the MACl additive to the perovskite precursor solution, this intermediate liquid phase enables the well-controlled growth of large grains up to 3 μm, highly uniform morphology, and higher crystallinity in the final CH 3 NH 3 PbI 3 perovskite films. The high-quality CH 3 NH 3 PbI 3 film derived from the CH 3 NH 3 PbI 3 ·MACl· x CH 3 NH 2 phase leads to enhanced carrier lifetime and reduced charge-trap density and nonradiative recombination of the perovskite films. In addition, the defect healing and reduced grain boundaries also greatly improve the environmental stability in ambient air. The perovskite solar cells made via the CH 3 NH 3 PbI 3 ·MACl· x CH 3 NH 2 phase exhibit high power conversion efficiency of 18.4%, much higher than that of the perovskite solar cells made without MACl (15.8%).