Tailoring the Intermediate Phase to Control Formation of γ-CsPbI₃Films

Controlling the crystallization pathway of inorganic CsPbI₃perovskite is essential for achieving high efficiency and stability in optoelectronic devices. Here, we report a solvent-engineering strategy that combines an antisolvent process with vacuum treatment (AVT) to modulate evaporation dynamics of the precursor, guiding the formation of highly oriented (CH₃)₂NH₂PbI₃(DMAPbI₃) and Cs₄PbI₆intermediate phases. Synchrotron and in situ analyses revealed correlations between intermediate orientation and γ-CsPbI₃crystallinity. This directional crystallization pathway promotes vertical alignment and grain enlargement in γ-CsPbI₃films, resulting in fewer voids, lower defect densities, and reduced tensile strain. Photovoltaic devices based on AVT-processed films achieved a power conversion efficiency of 18.47% with a fill factor of 83.14% and retained 101.9% of their initial efficiency after 526 h without encapsulation. This study first reports that the quality of DMAPbI₃and Cs₄PbI₆intermediates, controlled by combination of antisolvent and vacuum treatment, plays a crucial role in achieving high-quality γ-CsPbI₃films.