Multidentate Phosphine Oxide Ligands for Regulating Surface Coordination and Electronic Coupling in CsPbI ₃ Quantum Dot Solar Cells

All-inorganic CsPbI 3 perovskite quantum dots (PQDs) suffer from a long-standing trade-off between effective surface passivation and efficient interdot charge transport. Here, we identify ligand denticity as a key parameter governing this balance using mono-, bi-, and tetradentate phosphine oxide ligands. Increasing denticity strengthens surface coordination and suppresses defect-assisted recombination but simultaneously introduces steric constraints that weaken interdot electronic coupling. Density functional theory calculations reveal that the bidentate ligand 2-TPPO preferentially adopts an energetically favorable bridging configuration between adjacent PQDs, enabling both strong surface binding and efficient carrier transport. Consistent with this mechanism, 2-TPPO-treated PQD solids exhibit reduced trap density and improved structural ordering. Consequently, CsPbI 3 PQD solar cells achieve an efficiency of 17.1% with enhanced operational stability. These findings establish ligand denticity as a molecular design principle for balancing defect passivation and electronic coupling in PQD solids.