Dual Function of Surface Alkali-Gas Erosion on SnO₂ for Efficient and Stable Perovskite Solar Cells

The electrical character and interface contact of the electron transport layer (ETL) play a critical role in high-efficiency planar perovskite solar cells. Here, a dual functional surface alkali-gas erosion (SAE) method is proposed based on the unique chemical properties of the amphoteric oxide. First, during the SAE process, SnO2 can react with alkaline gas slightly, and the chemical reaction mechanism is elucidated, which leads to the crystal fusion of the SnO2 surface, bringing an improved electron mobility and an excellent interface contact between the SnO2 ETL and perovskite layer. Second, the SAE method introduced the −NH2 group on the SnO2 surface chemically, which can provide a nucleation site for the perovskite crystal and promote the growth of the perovskite film; meanwhile, the −NH2 group connected chemically with SnO2 also serves as a bridge-link by replacing the organic cation at the perovskite/SnO2 interface, which effectively enhances the interfacial charge transport and the perovskite crystallinity. As a consequence, devices with SAE achieve a champion PCE of 21.10%, and the average PCE is increased from 18.07 to 20.30%, which mainly results from the increase of short-circuit current density from 22.34 to 24.19 mA cm–2. Moreover, the optimized devices retain 86% of its initial PCE (compared with 41% of the control device) after 60 days at room temperature with 40–50% humidity.