Surface Passivation with Lattice‐Matched Bidentate Ligand Enabling High‐Performance Perovskite Quantum Dot Photodetectors

Surface halide vacancies are prevalent on lead halide perovskite (LHP) quantum dots (QDs) due to their intrinsically low formation energy, and they serve as dominant non-radiative recombination centers that degrade optoelectronic performance. While ligand exchange has been commonly used to mitigate these surface defects, the influence of multidentate ligand geometry on binding interactions with QD surfaces remains largely unexplored. In this study, we demonstrate that controlling the spatial configuration of bidentate phosphine ligands by adjusting the length of the alkyl bridge connecting the phosphorus atoms can achieve better lattice matching to the CsPbI₃ QD surface and thereby enhance ligand-surface binding strength. By comparing DPPM and DPPP, which possess distinct P-P separations, we show that the lattice-matched ligand DPPP exhibits stronger binding affinity due to improved steric compatibility with the QD lattice. As a result, DPPP-treated QDs exhibit significantly higher photoluminescence quantum yield and lower trap density than their DPPM-treated counterparts. Photodiodes incorporating DPPP-passivated QDs achieve enhanced responsivity and reduced dark current, reaching a specific detectivity of 5.67 × 10¹² Jones. These findings highlight the critical role of ligand-lattice geometric matching in improving interfacial coordination and device performance, offering a new molecular design strategy for high-performance LHP QD-based optoelectronics.