Enhanced Efficiency and Stability of All‐Inorganic CsPbI 2 Br Perovskite Solar Cells by Organic and Ionic Mixed Passivation

All‐inorganic perovskites have been intensively investigated as potential optoelectronic materials because of their excellent thermal stability, especially for CsPbI 2 Br. Herein, the authors studied the effects of mixed passivation utilizing organic phenylethylammonium bromide and inorganic ionic cesium bromide (PEABr + CsBr) on the all‐inorganic perovskite (CsPbI 2 Br) solar cells for the first time. The treatment with different passivation mechanisms enhances the perovskite film quality, resulting in uniform surface morphology and compact film with low trap density. Besides, the passivation improves the energy level alignment, which benefits the hole extraction at the perovskite/HTL interface and drives the interface electron separation, suppressing the charge recombination and realizing a high open‐circuit voltage ( V oc ). Finally, the device represents a high power conversion efficiency (PCE) of 16.70%, a V oc of 1.30 V, and an excellent fill factor (FF) of 0.82. The V oc loss and high FF should be among the best values for CsPbI 2 Br based devices. Furthermore, the treated devices exhibit remarkable long‐term stability with only 8% PCE loss after storing in a glove box for more than 1000 h without encapsulation.