Photoexcited dynamics of electrons and holes in semiconductor quantum dots (QD), including phonon-induced relaxation, multiple exciton generation, and recombination (MEG and MER), were simulated by combining ab initio time-dependent density functional theory and non-adiabatic (NA) molecular dynamics. These nonequilibrium phenomena govern the optical properties and photoexcited dynamics of QDs, determining the branching between electronic processes and thermal energy losses. Our approach accounts for QD size and shape as well as defects, core�shell distribution, surface ligands and charge trapping, which significantly influence the properties of photoexcited QDs. The method creates an explicit time-domain representation of photoinduced processes and describes various kinetic regimes owing to the non-perturbative treatment of NA couplings in the quantum dynamics. QDs of different sizes and materials, with and without ligands, are considered. The simulations provide direct evidence that the high-frequency ligand modes on the QD surface play a pivotal role in the electron�phonon relaxation, MEG, and MER. We also found logarithmic temperature dependence of the Auger rates in semiconductor QDs which agrees well with the experimental observation. This anomalous temperature dependence is not determined by static electronic structures of the QDs depending on temperature, but attributed to dynamical electron-phonon couplings, directly demonstrating that the Auger processes are actually induced by the electron-phonon couplings. Our findings suggest that high-frequency and broad phonon modes of a QD surface dictate efficient Auger dynamics of QDs. The insights reported here suggest novel routes for controlling the photoinduced processes in semiconductor QDs and lead to new design principles for increasing efficiencies of photovoltaic devices.

Photoexcited electron and hole dynamics coupled to phonon modes in semiconductor quantum dots

246th National Meeting (2013)

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