High Efficiency (16.37%) of Cesium Bromide—Passivated All‐Inorganic CsPbI2Br Perovskite Solar Cells

All‐inorganic CsPbI 2 Br perovskite has attracted increasing attention, owing to its outstanding thermal stability and suitable bandgap for optoelectronic devices. However, the substandard power conversion efficiency (PCE) and large energy loss ( E loss ) of CsPbI 2 Br perovskite solar cells (PSCs) caused by the low quality and high trap density of perovskite films still limit the application of devices. Herein, the post‐treatment of evaporating cesium bromide (CsBr) is utilized on top of the perovskite surface to passivate the CsPbI 2 Br–hole‐transporting layer interface and reduce E loss . The results of microzone photoluminescence indicate that the evaporated CsBr gathered at the grain boundaries of CsPbI 2 Br layers and Br‐enriched perovskites (CsPbI x Br 3− x , x < 2) are formed, which can provide protection for CsPbI 2 Br. Therefore, the gaps between crystal grains are filled up, and the recombination loss of the all‐inorganic CsPbI 2 Br PSCs is reduced accordingly. The champion device exhibits high open‐circuit voltage and a PCE of 1.271 V and 16.37%, respectively. This is the highest reported PCE among all‐inorganic CsPbI 2 Br PSCs reported so far. In addition, the stability of CsPbI 2 Br PSCs is effectively improved by CsBr passivation, and the device without encapsulation can retain 86% of its initial PCE after 1368 h of storage, which is beneficial for practical applications.