Ligand Exchange Strategy in Quantum Dot Solids Towards Highly Sensitive Infrared Photodetectors

As-synthesized quantum dots (QDs) are typically capped with long organic ligands that hinder charge transport in QD solids, limiting device performance. Engineering QD surface chemistry through ligand exchange is therefore crucial for achieving high-sensitivity infrared (IR) photodetectors. In this work, we systematically investigate how ligand exchange affects the optoelectronic properties, quantum confinement, and surface chemistry of lead chalcogenide (PbX, X =Se, S) QD films. A series of short-chain ligands and a two-step hybrid ligand treatment combining organic and inorganic species were explored. We find that ligand exchange effectively suppresses PbX oxidation, enhancing film stability compared to untreated QDs. Two-step ligand treatments produce uniform surfaces and significantly improve charge carrier mobility, whereas one-step processes often result in surface cracking and poor transport. Optimization of ligand concentration and film thickness yields efficient IR photodetector performance. In particular, PbX QD films treated with 3-mercaptopropionic acid (MPA) and zinc iodide (ZnI₂) exhibit reduced dark current, enhanced photocurrent, and improved carrier mobility and conductivity relative to other treatments. This simple yet effective passivation strategy provides a promising pathway for developing high-performance QD-based optoelectronic devices, especially for IR photodetection applications.