Extrinsic Doping and Interface Engineering of Nonaqueous Tin Oxide Nanocrystals for Efficient Perovskite Solar Cells

ABSTRACT Tin oxide (SnO 2 ) is an excellent electron transport layer (ETL) in n‐i‐p perovskite solar cells (PSCs), but its prevalent aqueous processing limits application in p‐i‐n or tandem architectures. Herein, a stable, nonaqueous platform of conductive Sb‐doped SnO 2 (ATO) nanocrystals (∼4 nm) is developed, enabling high‐performance ETLs for both device configurations. This platform is built upon a tert ‐butanol‐based synthesis, yielding nanocrystals that are near‐monodispersed and stable in low‐polarity solvents for over one year, addressing the fundamental processing incompatibility. Within this platform, coupled materials engineering is performed: Sb doping suppresses oxygen vacancies while preserving high crystallinity, and interface regulation with a phosphonic acid molecule (3‐aminopropylphosphonic acid) optimizes energy‐level alignment and suppresses non‐radiative recombination. Consequently, this versatile ATO nanocrystal platform delivers impressive efficiencies: a champion (average) power conversion efficiency (PCE) of 26.2% (25.2 ± 0.46%) in n‐i‐p PSCs and, notably, 21.2% (20.4 ± 0.42%) in p‐i‐n PSCs without any buffer layer—the highest for a solution‐processed, sole SnO 2 ‐based ETL in this challenging architecture. This work provides a viable processing pathway that bridges the compatibility gap for SnO 2 ETLs in both n‐i‐p and p‐i‐n PSCs.