Multifunctional Molecule Engineered SnO₂ for Perovskite Solar Cells with High Efficiency and Reduced Lead Leakage

Outstanding performance of perovskite solar cells (PSCs) is closely linked to the optoelectrical properties of charge transporting layers. Herein, amino trimethylene phosphonic acid (ATMP) and KOH are mixed (ATMP-K) and incorporated in a SnO₂ precursor solution to significantly improve the performance of the electron transport layer (ETL) SnO₂ in PSCs. Combining density functional theory (DFT) calculations and experiments, it is demonstrated that ATMP-K effectively passivates the oxygen vacancy and reduces the hydroxyl groups on the surface of SnO₂, resulting in a larger perovskite grain size and better energy-level alignment with perovskites. ATMP-K boosts the power conversion efficiency (PCE) of the PSCs from 20.99% to 23.52%. When applying in a perovskite/silicon heterojunction tandem solar cell, the device delivers an efficiency up to 24.75% with a high V_OC of 1.94 V, compared with 22.67% and 1.85 V of the reference cells. Furthermore, ATMP-K-modified PSCs also show extraordinary ability to absorb Pb²⁺ ions after their degradation in water, offering a facile strategy for reducing Pb leakage.