Surface Reconstruction of CdSe Quantum Dots Driven by Electron Accumulation and External Electric Fields

Electroluminescent applications of quantum dot light-emitting diodes (QLEDs) remain challenging because of the performance degradation and lifetime reduction of blue-light-emitting quantum dots (QDs). Although several strategies have been proposed to promote the QLEDs’ performances, the mechanism of the performance degradation needs further theoretical exploration. In a typical electroluminescent process, QDs are placed under an electric field accompanied by electron/hole injection. Electron accumulation may occur when the injection rate of electrons is faster than that of holes; however, its effect, as well as its coupling with the external field, on the structural stability and optical properties of ligated QDs has not yet been fully studied at the atomistic scale. First-principles calculations and ab initio molecular dynamic simulations in this work reveal that the electron accumulation in ligated CdSe QDs has a tendency to localize at one or two surface Cd atoms, making them reduce and change their bonding with surrounding atoms. The reduction of surface Cd atoms results in remarkable surface reconstruction and shifts in optical absorption peaks. Moreover, the injected electron couples with the external field, and their coupling is enhanced when two electrons are accumulated. The revealed molecular mechanism complies with available observations and contributes to the theoretical understanding of QD instability in electroluminescent applications.