Unraveling the Antisolvent Bathing Effect on CsPbI3 Crystallization under Ambient Conditions

Antisolvent treatment has been developed to effectively fabricate dimethylammonium-iodide (DMAI)-assisted CsPbI3 perovskite solar cells (PSC) under moisture conditions. However, a clear understanding of its effect on the crystallization mechanism is still elusive. Here, the antisolvent bathing effect on DMAI-assisted CsPbI3 crystallization is investigated under ambient conditions. For films bathed into antisolvents with Lewis basic oxygen (i.e., diethyl ether, anisole, ethyl acetate, and methyl acetate), rapid crystallization kinetics are observed due to the interaction between Cs4PbI6 and antisolvent in the form of the adduct. The Cs4PbI6-antisolvent adduct lowers the transformation energy barrier, thereby enabling immediate phase transformation to CsPbI3 as soon as DMAPbI(3) is decomposed. Based on this observation, a new crystallization mechanism is proposed for DMAI-assisted CsPbI3 in which Cs4PbI6, instead of DMAPbI(3), plays the role of the predominant phase of crystallization. Accelerated crystallization due to anisole antisolvent bathing results in a uniform film morphology and better coverage with fewer defects and pinholes. This enhances the power conversion efficiency of the n-i-p-structured PSCs based on anisole-bathed CsPbI3 to 18.84%, even under moisture conditions.