All‐inorganic CsPbIBr2 perovskite solar cells (PSCs) recently demonstrated great superiority for application in tandem and semitransparent photovoltaics because of their excellent phase stability. However, compared to state‐of‐the‐art PSCs, the inferior film quality is harmful for the photovoltaic performance improvement. Herein, a novel ionic additive, tetrabutylammonium hexafluorophosphate (TBAPF6), is employed to improve the all‐inorganic CsPbIBr2 perovskite film quality and passivate detrimental defects. By assembly into carbon–electrode‐based solar cells, a champion efficiency as high as 10.57% is achieved, which is much higher than that of a control device with 8.30% efficiency, mainly attributed to the suppressed non‐radiative recombination. More importantly, the presence of alkyl chains and fluorine atoms in TBAPF6 significantly increases the hydrophobicity of perovskite films and therefore improves the long‐term stability under harsh conditions without encapsulation.