# Temperature-Optimized Liquid-Phase Iodide Ligand Exchange Enables Low-Trap Solution-Processed PbS Quantum Dot Photodetection at 940 nm

## TL;DR

This paper shows that optimizing the temperature during a chemical treatment of PbS quantum dots improves their performance in photodetectors.

## Contribution

The study introduces a temperature-optimized ligand-exchange method that enhances photodetector performance by reducing defects and trap losses.

## Key findings

- Ligand exchange at 40°C maximizes iodide passivation and minimizes oxygen-related defects in PbS quantum dots.
- Photodetectors made from 40°C-treated QDs show 52% external quantum efficiency at 940 nm.
- The method enables n-type band alignment and improved device reproducibility.

## Abstract

PbS quantum dots (QDs) synthesized with oleic acid (OA) ligands suffer from poor charge transport in solid films, necessitating ligand exchange to shorter halide ligands for optoelectronic applications. This study investigates how ligand-exchange temperature governs OA-to-iodide substitution in PbS QDs. At 40 °C, the QD surface shows maximized halide passivation (I/Pb = 0.60) and minimized oxygen-related species (O/Pb = 0.23), suggesting reduced oxygen-associated defect formation and enabling n-type band alignment and reduced trap-mediated losses. PbS QD photodetectors fabricated from the 40 °C-treated QDs have 52% external quantum efficiency (EQE) at 940 nm (vs. 39% at 25 °C), with a responsivity of 0.394 A/W and an estimated detectivity of 2.1 × 1013 Jones. Temperature optimization of ligand-exchange provides a straightforward lever to improve device performance and reproducibility.