AbstractThe buried interface between the perovskite and the electron transport layer (ETL) plays a vital role for the further improvement of power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). However, it is challenging to efficiently optimize this interface as it is buried in the bottom of the perovskite film. Herein, a buried interface strengthening strategy for constructing efficient and stable PSCs by using CsI‐SnO₂ complex as an ETL is reported. The CsI modification facilitates the growth of the perovskite film and effectively passivates the interfacial defects. Meanwhile, the gradient distribution of Cs⁺ contributes to a more suitable band alignment with the perovskite, and the incorporation of Cs⁺ into the perovskite at the bottom interface enhances the resistance against UV illumination. Eventually, a significantly improved PCE up to 23.3% and a much‐enhanced UV stability of FAPbI₃‐based PSCs are achieved. This work highlights the importance of cesium‐enhanced interfaces and provides an effective approach for the simultaneous realization of highly efficient and UV‐stable perovskite solar cells.