Dual Interfacial Modifications by a Natural Organic Acid Enable High-Performance Perovskite Solar Cells with Lead Shielding

Effective interfacial modification of the perovskite layer is a feasible approach to improve the efficiency and stability of perovskite solar cells (PSCs). Herein, we introduce a dual interfacial modification approach utilizing a natural organic acid, citric acid (CA), to enhance both interfaces adjacent to the crucial perovskite layer within the PSC structure. First, a CA thin layer is deposited on the top of a SnO₂ electron transport layer to mitigate the corrosive effects of alkaline impurities in SnO₂ on the perovskite film and to control the crystal growth of the perovskite. Then, the perovskite film is post-treated with CA to adjust the surface condition and passivate the defects on the film surface; thus, the interface contact around perovskite is strengthened, thereby facilitating charge transfer at the interfaces. Besides, CA also provides an in situ suppression of lead leakage in case the perovskite film is destroyed, owing to the strong chelating interactions of carboxyl groups with Pb²⁺. The photovoltaic performance and stability of the final PSCs are significantly enhanced, with the power conversion efficiency (PCE) increasing from 21.02 to 24.20%. This optimization of the important interfaces adjacent to the perovskite layer through surface treatment with a natural organic acid offers a practical method for enhancing the performance and stability of environmentally friendly PSCs.