Urea Derivative‐Promoted CsPbI2Br Perovskite Solar Cells with High Open‐Circuit Voltage

Inorganic perovskite solar cells (PSCs) have witnessed extraordinary advances owing to their prominent stability against thermal aging. However, they suffer from a phase transition from black phase to yellow phase under ambient conditions and serious energy losses relative to the optical bandgap. Herein, urea (Ur) and methyl‐substituted urea (Me‐Ur) additives are used to modulate the lattice structure and crystallinity of the CsPbI 2 Br, facilitating phase stability and high device performance. The Me‐Ur can attenuate the strong hydrogen bonding networks in the Ur, which leads to stronger coordination of the carbonyl group with undercoordinated Pb 2+ , more efficiently passivating the defect states and suppressing the lattice distortion of the [PbI 6 ] 4− octahedra in the CsPbI 2 Br perovskite. Consequently, a champion power conversion efficiency of 16.5% with an open‐circuit voltage up to 1.33 V is obtained for the CsPbI 2 Br+Me‐Ur‐based PSCs, accompanied by enhanced stability under continuous illumination at a temperature of 45 ± 5 °C. These results emphasize the importance of regulating the lattice distortion by the urea derivative to implement efficient and stable inorganic CsPbI 2 Br PSCs.