Electrochemical Stability and Trap-State-Mediated Photoluminescence Modulation of InP-Based Quantum Dots

Indium phosphide (InP) quantum dots (QDs) are promising heavy-metal-free materials for optoelectronics, but their redox stability, trap-state landscape, and charge carrier dynamics are not well understood. Here we investigate InP and InP/ZnSe/ZnS QD films with different ligands by using spectroelectrochemistry. For both core-only and core/shell/shell QD films, the absorption spectra remain unchanged during charging, indicating that injected charges do not populate the conduction or valence bands. InP/ZnSe/ZnS QD films with original ligands exhibit reversible photoluminescence (PL) modulation: an increase at modest cathodic potentials, followed by quenching at more negative potentials. Solid-state ligand exchange using ethylenediamine (2DA) and sodium sulfide (Na2S) enhances conductivity and induces stronger PL changes at both cathodic and anodic potentials. These results are in line with the population of electron traps at modest cathodic potentials (i.e., near the midbandgap), suppressing nonradiative recombination and increasing the PL. At more negative potentials, electrochemical reactions of surface species result in new trap states quenching the PL. Our findings provide insights into the stability and trap-state-mediated carrier dynamics during electrochemical charging of InP-based QDs.