Insights Into Coverage -Dependent Carboxylate Passivation And Surface Termination Of InP Quantum Dots For Optimized Optoelectronic Performance

Abstract

Indium phosphide quantum dots (InP QDs) have emerged as promising alternatives to Cd-based materials for QLED applications, offering high photoluminescence quantum yield (PLQY) and a wide color gamut. Owing to their large surface-to-volume ratio, the surface structure plays a decisive role in governing the optoelectronic properties of InP QDs. Among the crystal facets, the polar (111) and (-111) surfaces are particularly challenging because they can be either In- or P-terminated, necessitating a careful evaluation of their thermodynamic stability. In this work, first-principles calculations were performed to determine the surface energies of InP(111) with In- or P-terminated, yielding 51.25 meV/Å2 and 53.47 meV/Å2, respectively. These results indicate that the In-terminated surface is thermodynamically more stable under ideal conditions. Surface passivation by native carboxylate ligands (described as C2H5COOˉ) was further examined, revealing diverse binding motifs and uniform charge redistribution that stabilize colloidal growth. However, density of states analysis shows that while low ligand coverage increases the band gap (1.69 eV vs. 1.55 eV for pristine InP(111)), high coverage introduces hole trap states that reduce the gap (1.12 eV) and potentially limit PLQY. Integrated DOS analyses further demonstrate that ligand coverage strongly modulates PLQY. Specifically, at 25% carboxylate coverage, the PLQY displays an enhancement of approximately 4%, whereas coverage beyond 50% induces nonradiative pathways that diminish radiative efficiency. These findings provide atomic-scale insights into the interplay between surface termination, ligand passivation, and optoelectronic performance, offering design principles for optimizing the quantum efficiency of InP QDs in light-emitting applications.