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 CsPbI2Br, 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 Pb2+, more efficiently passivating the defect states and suppressing the lattice distortion of the PbI6 octahedra in the CsPbI2Br perovskite. Consequently, a champion power conversion efficiency of 16.5% with an open-circuit voltage up to 1.33 V is obtained for the CsPbI2Br+Me-Ur-based PSCs, accompanied by enhanced stability under continuous illumination at a temperature of 45 +/- 5 degrees C. These results emphasize the importance of regulating the lattice distortion by the urea derivative to implement efficient and stable inorganic CsPbI2Br PSCs.