Intermediate-Phase-Modified Crystallization for Stable and Efficient CsPbI₃ Perovskite Solar Cells

All-inorganic CsPbI₃ perovskite solar cells (PSCs) are becoming desirable for their excellent photovoltaic ability and adjustable crystal structure distortion. However, the unsatisfactory crystallization of the perovskite phase is unavoidable and leads to challenges on the road to the development of high-quality CsPbI₃ perovskite films. Here, we reported the intermediate-phase-modified crystallization (IPMC) method, which introduces pyrrolidine hydroiodide (PI) before the formation of the perovskite phase. The hydrogen bonding, which originates from the interaction between the -NH in PI and the dimethylammonium iodide (DMAI) from the precursor solution, improved the crystallization conditions and further prompted the transition from the DMAPbI₃ phase to CsPbI₃ perovskite phase. The application of the IPMC method not only decreased the trap density but also changed the energy alignment for better separation of electron-hole pairs. As a result, the devices based on the PI-CsPbI₃ perovskite films reached an efficiency of 18.72% and maintained 85% of their initial PCE after 1000 h of being stored in an ambient environment (∼25% RH, 25 °C). This work stimulates inspiration on how to conveniently fabricate high-quality perovskite films in industry.