High-Affinity Ligand-Enhanced Passivation of Group III-V Colloidal Quantum Dots for Sensitive Near-Infrared Photodetection

Group III-V colloidal quantum dots (CQDs) are promising infrared-absorbing materials that overcome the limitations of their regulated heavy-metal-containing counterparts, including Pb-, Cd-, and Hg-based materials. However, their surfaces and ligand chemistry remain unexplored, impeding sufficient ligand exchange. Therefore, approaches for selecting suitable exchange/passivation-enabling ligands for group III-V CQDs must be devised. Based on the hard-soft acid-base theory, diverse metal halide ligands and their interactions with InAs CQD surfaces were scrutinized in this study. Experimental investigations and density functional theory calculations indicated that hard-type Sn-based metal halide ligands exhibited a high affinity for the hard-type As-rich surface of InAs CQDs. Attaching different halides (X) affected the photoresponse performance of InAs-CQD-based devices. Here, high-affinity SnBr2 ligands were selected to fabricate the InAs-CQD-based photodiode, which exhibited the highest external quantum efficiency of 43.1% and responsivity of 0.36 A W-1 at an exciton peak of 1020 nm among previously reported InAs-CQD-based photodiodes.