The bi-functional additive of ammonium benzenesulfonate enables the fabrication of low-defect and high-performance perovskite solar cells.

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 (≈22% RH, ≈25 °C).

Despite demonstrating remarkable power conversion efficiencies (PCEs), perovskite solar cells (PSCs) have not yet achieved their full potential. In particular, the interfaces between the perovskite and charge transport layers account for the vast majority of the recombination losses. Interfacial contact and band alignment between the lowtemperature-processed TiO 2 electron transport layer (ETL) and the perovskite are essential to minimize nonradiative recombination losses. In this study, a CeO x interlayer is employed to modify the perovskite/TiO 2 interface, and the charge transport properties of the devices are investigated. The bilayer-structured TiO 2 /CeO x ETL leads to the modification of the interface energetics, resulting in improved electron extraction and reduced nonradiative recombination in the PSCs. Devices based on TiO 2 /CeO x ETL exhibit a high open-circuit voltage (V oc ) of 1.13 V and an enhanced PCE of more than 20% as compared with V oc of 1.08 V and a PCE of approximately 18% for TiO 2 -based devices. Moreover, PSCs based on TiO 2 / CeO x ETL maintain over 88% of their initial PCEs after light illumination for 300 min, whereas PSCs based on TiO 2 ETL almost failed. This study provides an efficient strategy to enhance the PCE and stability of PSCs based on a lowtemperature-processed TiO 2 ETL.