Structurally Reinforced All-Inorganic CsPbI2Br Perovskite by Nonionic Polymer via Coordination and Hydrogen Bonds

The all-inorganic CsPbI2Br perovskite with superior thermal durability faces challenges of low-phase stability and high moisture sensitivity. Herein, a nonionic additive of polyethyleneimine (PEI) with multiple amino groups is introduced to form hydrogen bond with I-/Br(-)ions and coordinate with Pb2+/Cs(+)ions simultaneously. The strong interplay between PEI and CsPbI2Br achieves a well-controlled grain size, reduced defects, and reinforced phase structure of CsPbI2Br film, which boosts the power conversion efficiency (PCE) of perovskite solar cells to 15.48%. The hydrophobic long alkyl chain of PEI greatly improves the humidity resistance, retaining 81.9% of initial PCE of zjr unsealed device under 20 +/- 5% relative humidity (RH) for 500 h. Remarkably, a PCE of 13.37% is achieved by the device based on CsPbI2Br-PEI film processed under ambient condition (approximate to 22% RH, approximate to 25 degrees C).