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

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.