The Synergistic Effect of Phosphonic and Carboxyl Acid Groups for Efficient and Stable Perovskite Solar Cells

Reducing the interfacial defects between the perovskite/electron transport layer (ETL) is the key point to improving the efficient and stable performance of perovskite solar cells (PSCs). In this study, two self-assembled molecules ((aminomethyl)phosphonic acid and glycine) with different functional groups (phosphonic acid (-H₂PO₃) and carboxylic acid (-COOH)) were mixed to form the buried bottom interface of PSCs. The synergistic effect of -H₂PO₃ with its higher anchoring ability and -COOH with its fast carrier transport improved the performance of PSCs. Additionally, the SnO₂ modified by mixed self-assembly molecules (M-SAM) showed a more appropriate energy level alignment, favoring charge transport and minimizing energy loss. In addition, the amine group (-NH₂) on the two small molecules effectively interacted with uncoordinated Pb²⁺ in perovskite and improved the quality of the perovskite films. Consequently, the (FAPbI₃)_0.992(MAPbBr₃)_0.008 PSCs with M-SAM reached a PCE of 24.69% (0.08 cm²) and the perovskite modules achieved a champion efficiency of 18.57% (12.25 cm² aperture area). Meanwhile, it still maintained more than 91% of its initial PCE after being placed in nitrogen atmosphere at 25 °C for 1500 h, which is better than that of the single-SAM and control devices. Further reference is provided for the future commercialization of perovskite with efficient and stable characteristics.