Quasi-Quantum Dots-Induced Stabilization of α-CsPbI3 Perovskite for High-Efficiency Solar Cells

All-inorganic cesium lead iodide perovskites (CsPbI3) are promising materials for efficient solar cells. However, they suffer from the formation of an undesired yellow δ-phase under ambient conditions. Herein, we provide a novel strategy to in-situ prepare quasi-quantum dots (QQD) CsPbI3 films by using a new ligand, adamantan-1-yl methanammonium (AMDA), with ultralow contents (~ 0.25 wt%) in the perovskite films. Strong interaction and charge coupling between ligands and nanocrystals significantly increase surface Gibbs energy of CsPbI3 and suppress the grain sizes to around 30 nm, which effectively prevents the black α-phase from the destruction of moisture and heat. By reducing the trap density of states in the QQD CsPbI3 films, the all-inorganic PSCs exhibit a power conversion efficiency of 13.5%. Most importantly, the QQD CsPbI3 films can substantially keep as α-phase and the QQD-based PSCs retain 90% of its initial efficiency after storage either in ambient condition for 30 days or 85°C heating for 336 h. These results indicate that in-situ preparing QQD films are a potential strategy to effectively improve the long-term stability of all inorganic perovskite materials.