Coordination-Driven Neutralization of SnO₂ Colloids for Suppressing Buried Interfacial Deprotonation in Perovskite...

Commercial SnO₂ 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 SnO₂/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 SnO₂ colloidal solutions. PBTC effectively neutralizes excessive OH^- while strongly coordinating with SnO₂ 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 SnO₂ 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.