A Key 2D Intermediate Phase for Stable High‐Efficiency CsPbI2Br Perovskite Solar Cells

Abstract Inorganic CsPbI 2 Br perovskite is promising for solar cell applications due to its excellent thermal stability and optoelectronic characteristics. Unfortunately, the current high‐efficiency CsPbI 2 Br perovskite solar cells (PSCs) are mostly fabricated in an inert atmosphere due to their instability to moisture. Herein, a low‐dimensional intermediate‐assisted growth (LDIAG) method is reported for the deposition of CsPbI 2 Br film in ambient atmosphere by introducing imidazole halide (IMX: IMI and IMBr) into the precursor solution to control both nucleation and growth kinetics. The IMX first combines with PbI 2 in the precursor film to form a 2D intermediate which then gradually releases PbI 2 to slowly form high‐quality CsPbI 2 Br film during annealing. It is found that the LDIAG method produces a uniform, highly crystalline, pinhole‐free, and stable CsPbI 2 Br film with low defect density. Consequently, the solar cell efficiency is increased to as high as 17.26%, one of the highest for this type of device. Furthermore, the bare device without any encapsulation shows excellent long‐term stability with ≈86% of its initial efficiency retained after being exposed to the ambient environment for 1000 h. This work provides a perspective to tune the intermediate phases and crystallization pathway for high‐performance inorganic PSCs formed under ambient conditions.