Defect Passivation and Stress Regulation via Bidentate Anchoring of Lewis Base for High-Efficiency CsPbI Solar Cells.

All-inorganic CsPbI perovskites film prepared via the low-temperature solution method often suffers from numerous defects during the crystallization process. Passivators used for surface passivation typically contain monofunctional groups, including sulfur, nitrogen, and oxygen. These monodentate groups bind to uncoordinated Pb by sharing electron pairs, thereby reducing surface defects. However, the monodentate anchoring formed is relatively weak and susceptible to be damage due to its low bond strength. Herein, a bidentate Lewis base, 2-(2-pyridyl)ethylamine (2-PyEA), containing a pyridine ring and an alkyl amine, is employed to passivate surface defects and stabilize CsPbI crystal structure. Compared to monodentate ligands, 2-PyEA displays significantly enhanced coordination ability. In particular, the bidentate anchoring of 2-PyEA introduces lattice distortion and transforms tensile stress into compressive stress within the CsPbI film, improving the structural stability of the perovskite material. As a result, the perovskite solar cells treated with 2-PyEA achieve impressive power conversion efficiencies (PCEs) of 21.35% and 17.19% for active areas of 0.09 and 1.0 cm, respectively. Notably, the device achieves an even higher PCE of 39.95% under indoor illumination conditions. The devices exhibit higher stability under ambient conditions with 5% relative humidity.