Lattice Oxygen‐Mediated Defect and Strain Regulation of SnO ₂ via Water‐Soluble Tb ₂ O ₃ for High‐Performance Perovskite Solar Cells

ABSTRACT Tin dioxide (SnO ₂ ) is widely used as the electron transport layer (ETL) in n‐i‐p type perovskite solar cells (PSCs), yet its practical potential is plagued by intrinsic oxygen vacancies and structural defects arising from chemical bath deposition (CBD). Herein, we propose a facile pretreatment strategy: integrating water‐soluble terbium oxide nanocrystalline (Tb ₂ O ₃ NCs) into the CBD‐derived SnO ₂ ETLs post‐cleaning but pre‐annealing. Systematic characterizations confirm that Tb ₂ O ₃ NCs induce a homogeneous SnO ₂ ‐Tb ₂ O ₃ composite interface via lattice oxygen‐mediated interfacial interaction. The abundant lattice oxygen of Tb ₂ O ₃ NCs mediates the passivation of SnO ₂ oxygen vacancies by replenishing oxygen defects. Meanwhile, the lattice oxygen‐regulated composite ETL exhibits enhanced carrier mobility, reduced surface roughness, and optimized surface energy, which synergistically promote perovskite crystallization into large‐grain films with superior light‐trapping capability. Consequently, the target PSCs achieve a champion power conversion efficiency (PCE) of 25.95%. Furthermore, the lattice oxygen‐mediated interfacial bonding mitigates ETL tensile strain under thermal cycling. These synergistic merits significantly enhance the device's humidity stability and operational stability in ambient air. This work provides a facile and scalable strategy to simultaneously engineer the defect state and structural integrity of SnO ₂ ETLs, offering valuable insights for the rational design of high‐efficiency and stable PSCs.