Enhanced ALD-SnO ₂ via Reactive Ion Etching-Assisted Surface Engineering for High-Performance and Stable Perovskite Solar Cells

Atomic layer deposition (ALD)-derived SnO 2 is an attractive electron transport layer (ETL) for scalable, high-performance perovskite solar cells (PSCs) owing to its excellent uniformity and compatibility with industrial processing. However, its intrinsic oxygen vacancies and surface imperfections hinder efficient charge extraction and interfacial stability. Herein, we introduce a reactive ion etching-assisted surface engineering (RIE-ASE) strategy that integrates chemical oxidation and physical ion bombardment to finely tailor the surface chemistry of ALD-SnO 2 . Our systematic surface engineering approach via RIE treatment demonstrates effective passivation of oxygen vacancies and formation of a well-defined SnO 2 surface, enhancing interfacial quality and electronic characteristics. The RIE-ASE-treated layers exhibit improved band alignment with perovskite absorbers and preserved morphological integrity. When incorporated into PSCs, the optimized RIE-ASE-modified single-layer ALD-SnO 2 yields a champion power conversion efficiency (PCE) of 23.13%, surpassing that of UV-Ozone-treated counterparts (21.88%). In addition, the RIE-ASE-treated devices exhibit negligible hysteresis and excellent reproducibility across 20 independent cells. Furthermore, the devices maintain over 95% of their initial PCE after 1000 h under dry room conditions (20 °C, 15% relative humidity), outperforming the 87% retention observed for the UV-ozone-treated control. This study establishes RIE-ASE as a rapid, vacuum-compatible, and highly reproducible method for defect passivation and energy-level tuning of ALD-SnO 2, providing a viable pathway toward scalable and commercially relevant fabrication of efficient and stable perovskite solar cells.