Vacuum-annealed bi-functionalized PbS quantum dots for low-noise and fast-response near-infrared photodetectors

Two-steps ligand-exchange bi-functionalization of PbS quantum-dot (QD) films are employed to realize the highly reliable and rapidly responsive photodetectors. We investigate how bi-functionalization strategy and post-anneal procedure regulates the structural coherence and surface chemistry of ligand-exchanged PbS-QD films, and how these material-level modifications translate into improved photodetector performances. Using reciprocal-space GIWAXS analysis combined with surface-sensitive XPS characterizations, we establish a direct correlation between lattice coherence enhancement, defect suppression, and reduced noise characteristics at 940-nm of light illuminations. The GIWAXS analysis reveals a 25–35 % increase in correlation length of PbS QDs, accompanied by the removal of hydroxyl species and coordinated ligands revealed by spectroscopic XPS identifications. These coupled structural and chemical evolutions are directly linked to the suppressed trap-assisted conduction and broadband noise fluctuations. The bi-functionalized PbS-QD photodetector delivers a detection responsivity of 0.77 A/W, noise-resolved detectivity of 1.68 × 10 10 Jones, and unexceptional response dynamics of 38 μs under 940-nm light illuminations.