Engineering Tin Oxide Electron Transport Layers for High‐Performance n‐i‐p Perovskite Solar Cells: Challenges, Strategies, and Prospects

Tin oxide (SnO 2 ) has emerged as a leading electron transport layer (ETL) in perovskite solar cells (PSCs), particularly in n‐i‐p architectures, due to its high electron mobility, wide bandgap, and exceptional thermal and chemical stability. However, several challenges remain unresolved, including inconsistent film quality, intrinsic lattice defects, energy‐level misalignment, and suboptimal interfacial engineering, all of which hinder the operational stability and long‐term performance of PSCs. In this review, we provide a detailed and systematic overview of recent progress in SnO 2 ‐based ETLs for n‐i‐p structured PSCs. Key topics include defect passivation strategies, band energy alignment engineering, and interfacial charge transport optimization. Special emphasis is placed on the latest developments in surface treatments, doping strategies, and interface modifications that enhance electron transport and device operational stability. We critically evaluate how these advances contribute to improve power conversion efficiency and device durability. By addressing these bottlenecks through rational engineering, SnO 2 is poised to play a pivotal role in pushing PSCs performance closer to its theoretical limit and facilitating future commercialization.