# Ligand Influence on CuInS2 Quantum Dot Photoconductive Films

## TL;DR

This paper studies how different ligands affect the performance of CuInS2 quantum dots in photodetection devices.

## Contribution

The study demonstrates that shorter ligands improve charge transport and photodetection performance in CuInS2 quantum dot films.

## Key findings

- MPA- and TGA-capped QD films showed 7–9 times higher current than DDT-capped films.
- TGA-capped QD devices had a photocurrent-to-dark current ratio of 2.6.
- TGA-capped QD devices responded well to 20 kHz pulsed UV excitation.

## Abstract

In this work, we investigate the effect of ligand chemistry on the optical and electrical properties of copper indium disulphide (CuInS2) quantum dots (QDs) and evaluate their suitability for photodetection with simple device structures. CuInS2 QDs capped with dodecanethiol (DDT) ligands were synthesized, followed by processes to exchange the DDT with thioglycolic acid (TGA), mercaptopropionic acid (MPA), or thioacetamide (TAA) ligands. Photoluminescence (PL) and UV-Visible absorption studies revealed that while TGA- and MPA-capped QDs retained strong emission, TAA-capped QDs exhibited significant quenching, indicating surface defect formation due to poor ligand binding. Metal–semiconductor–metal (MSM) test structures were fabricated using the QD films as the active layer to study their electrical properties under dark and UV-illuminated conditions. Devices based on MPA- and TGA-capped QD films demonstrated currents that were 7–9 times higher than those of devices with native DDT ligands, with significantly enhanced photocurrent-to-dark current ratios of 2.6 and 1.7, respectively, highlighting the effective charge transport pathways enabled by the shorter ligands. The device with TGA-capped QD film also responded well to 20 kHz pulsed UV excitation, underscoring the strong potential of this simple MSM structure for photodetection and optical switching applications.