Ligand effect on surface reconstruction in CdSe quantum dots driven by electron injection in electroluminescence processes†

Abstract

The short lifetime of blue quantum dots (QDs) in the electroluminescence process is indeed one of the main obstacles that hinder their applications in new display technologies. One of the speculations about the short lifespan is believed to be the reduction reactions at the interface between the QD and the ligand caused by electron injection, but little is known about how the reactions proceed. The evolution of geometrical and electronic structures of ligated (CdSe)₆ is simulated with the real-time time-dependent density functional theory (rt-TDDFT) method. Two distinct reactions are characterized in the QDs with different ligand types. One involves the localization of an electron at one specified surface atom, making the ligand separated from the QD, as well as large changes in the QD structures. The other involves the delocalization of an electron across the QD and the ligand, leading to only small changes. In the first case, the destroyed structure becomes irreversible once the ligand fails to re-bond with the QD after the electron–hole recombination. Our simulations provide direct evidence that the reduction reactions caused by electron injection are responsible for the performance loss of blue QDs in the electroluminescence process, and suggest that the delocalization of injected electrons is an interesting strategy for future studies.