Temperature-Optimized Liquid-Phase Iodide Ligand Exchange Enables Low-Trap Solution-Processed PbS Quantum Dot...

Area of Science:

• Materials Science
• Nanotechnology
• Optoelectronics

Background:

• Lead sulfide quantum dots (PbS QDs) synthesized with oleic acid (OA) ligands exhibit poor charge transport in solid films.
• Ligand exchange to shorter halide ligands is crucial for improving PbS QD optoelectronic applications.

Purpose of the Study:

• To investigate the effect of ligand-exchange temperature on OA-to-iodide substitution in PbS QDs.
• To optimize PbS QD surface passivation for enhanced optoelectronic device performance.

Main Methods:

• Investigated OA-to-iodide ligand exchange in PbS QDs at varying temperatures.
• Analyzed surface composition using elemental analysis (I/Pb and O/Pb ratios).
• Fabricated and characterized PbS QD photodetectors.

Main Results:

• Ligand exchange at 40°C maximized halide passivation (I/Pb = 0.60) and minimized oxygen-related species (O/Pb = 0.23).
• This optimal temperature reduced oxygen-associated defects, enabling n-type band alignment and minimizing trap-mediated losses.
• PbS QD photodetectors fabricated with 40°C-treated QDs showed a 52% external quantum efficiency (EQE) at 940 nm, compared to 39% at 25°C.

Conclusions:

• Temperature optimization of ligand exchange is a critical factor for improving PbS QD surface passivation.
• Optimized ligand exchange significantly enhances PbS QD photodetector performance, including EQE, responsivity, and detectivity.
• This straightforward method offers improved device performance and reproducibility for PbS QD-based optoelectronics.