Quantum-Dot-Induced Cesium-Rich Surface Imparts Enhanced Stability to Formamidinium Lead Iodide Perovskite Solar Cells

The stability of formamidinium lead iodide (FAPbI3) perovskites is generally improved by incorporating cesium (Cs) into the crystal structure. However, the effectiveness of this approach is limited by the intrinsically low solid-solubility of Cs in bulk FAPbI3. To circumvent this issue, we demonstrate a method that entails solution-deposition of high-Cs-content Cs1–xFAxPbI3 alloy quantum dots (QDs) onto a bulk Cs-lean FAPbI3-based thin film. This results in a thin film with a Cs-rich QD surface layer, which stabilizes the thin film against the ambient environment. Stable, efficient perovskite solar cells based on these new thin-film structures are demonstrated.