Passivation of Magnetron‐Sputtered SnO ₂ Via Ammonium Paratungstate for Enhanced Open‐Circuit Voltage in Perovskite Solar Cells

Magnetron sputtering is a highly promising method for fabricating all functional layers in perovskite solar cells. However, magnetron‐sputtered SnO 2 (sp‐SnO 2 ) films exhibit high defect density, leading to lower open‐circuit voltage ( V OC ), fill factor (FF), and power conversion efficiency (PCE) compared to spin‐coated films. Here, ammonium paratungstate (APT) is introduced on the surface of sp‐SnO 2 to passivate defects. The APT modification effectively passivates nonstoichiometric oxygen defects, suppresses nonradiative recombination, and improves heterojunction contact. Consequently, APT‐treated devices achieve significantly enhanced performance and stability, with a V OC of 1.041 V, FF of 77.78%, PCE of 20.54%, and retention of 80.98% initial efficiency after 1440 h of natural aging. This work demonstrates that APT passivation of sp‐SnO 2 enables high‐performance PSCs and provides a straightforward solution to improve the performance of sp‐SnO 2 electron transfer layer.