A First‐Principles Investigation of Electronic Structure and Stability of the γ‐CsPbI 3 Surface

Enhancing the stability of the photoactive phases of inorganic cesium lead iodide (CsPbI 3 ) perovskite is crucial for improving the long‐term performance of CsPbI 3 ‐based solar cells. Structural degradation, often initiated by surface defects and enthalpy‐driven phase transitions, remains a major challenge. In this study, we use density functional theory combined with surface grand potential analysis to systematically evaluate the thermodynamic stability and electronic properties of key CsPbI 3 surfaces—(001), (011), and (100)—with both stoichiometric and nonstoichiometric terminations. Our results demonstrate that the CsI‐terminated (001) surface is the most thermodynamically stable within the chemical potential region where bulk CsPbI 3 is stable. In contrast, the (011) and (100) surfaces achieve thermodynamic stability only via reconstruction into nonstoichiometric terminations. Electronic structure analysis further reveals that stoichiometric terminations on (011) and (100) surfaces tend to introduce metallic Pb 0 states or I 2 − ‐like dimers, whereas nonstoichiometric terminations effectively avoid such defect states. These findings highlight the essential role of surface termination engineering in stabilizing CsPbI 3 for efficient and durable photovoltaic applications.