Coordination‐Driven Neutralization of SnO ₂ Colloids for Suppressing Buried Interfacial Deprotonation in Perovskite Solar Cells

ABSTRACT

Commercial SnO ₂ colloidal solutions are widely used as an electron transport layer (ETL) in perovskite solar cells (PSCs). However, their intrinsic strong alkalinity, required for colloidal stability, creates a high proton‐affinity SnO ₂ /perovskite interface that promotes deprotonation of formamidinium (FA ⁺ ) cations, destabilizing the perovskite lattice and accelerating nonradiative recombination. Herein, the coordination‐driven neutralization strategy was proposed by introducing a multidentate acidic molecule, 2‐phosphonobutane‐1,2,4‐tricarboxylic acid (PBTC), to regulate commercial SnO ₂ colloidal solutions. PBTC effectively neutralizes excessive OH ⁻ while strongly coordinating with SnO ₂ surface through its phosphonic and carboxylic groups, thereby reconstructing the surface chemistry environment and stabilizing the colloidal dispersion under near‐neutral conditions. This strategy reduces the density of defects in SnO ₂ ETL, facilitating more efficient electron extraction and transport. More importantly, the resulting near‐neutral buried interface inhibits FA ⁺ deprotonation and mitigates non‐radiative recombination losses. Consequently, the optimized devices achieve a power conversion efficiency of 25.87%. The unencapsulated devices retain 94.18% of their initial efficiency after 1000 h under ISOS‐L‐2I conditions and 90.85% after 300 h of ultraviolet illumination. This work presents a new strategy for synergistically regulating colloidal chemistry and interfacial reactions through multidentate coordination, offering a promising pathway toward highly efficient and stable PSCs.