Interfacial Energy-Level Engineering with Diammonium Halide for Efficient and Stable Perovskite Solar Cells

Interfacial energy-level alignment is critical for the efficient charge extraction and suppression of nonradiative recombination in perovskite solar cells (PSCs). However, the specific role of halide substituents in diamine ligands in regulating this property is insufficiently understood. Here, halide-substituted diamine ligands (C6-DAX₂, X = Cl, Br, I) were employed to modulate the surface electronic structure of perovskite films. Stepwise halide substitution decreased the work function and simultaneously shifted the Fermi level upward, thereby reducing the conduction band offset with C₆₀. This interfacial modulation facilitates electron transport and mitigates recombination losses. As a result, inverted PSCs incorporating C6-DAI₂ deliver a champion power conversion efficiency of 25.0% and maintain 85% of their initial efficiency after 1100 h of continuous operation.