An electron transport layer (ETL) is vital for extracting carriers in perovskite solar cells (PSCs). SnO₂ with high electron mobility and excellent energy level matching with adjacent perovskites has been considered as an ideal electron transport material with excellent application prospects. However, some surface defects always exist on the SnO₂ films prepared by a solution method, which will cause non-radiative recombination at the ETL/perovskite interface. Herein, an interfacial engineering strategy is adopted to eliminate the surface defects and improve the interface performance by modifying the SnO₂ with ammonium polyacrylate (PANH₄). After the PANH₄ treatment, the interfacial defects of the SnO₂/perovskite film were reduced significantly and the electron transport was effectively facilitated by the denser SnO₂ layer, finally improving the power conversion efficiency (PCE) of PSCs. Besides, the grain size of the perovskite increases, simultaneously improving the stability of the device. As a result, the PCE of PSCs with an active area of 0.09 cm² was increased from 18.91% to 20.70%.