In the first part of my talk, I will describe our development of (dissipative) quantum transport theory for transient transport and its application on the understanding of quantum interference and decoherence in molecular electronics. Time-dependent quantum transport is a nontrivial problem, our development of equations of motion (EOMs) method significantly reduces the computational cost. In order to deal with the dissipation induced by electron-phonon interaction, we developed dissipative quantum transport theory for weak, strong and arbitrary electron-phonon coupling strength. In the second part, I will present our development of quantum mechanical approaches for modeling photovoltaic effect (PV) and electroluminescence (EL) processes in nanoscale. Based on nonequilibrium Green's function quantum transport equation and density functional tight-binding method, the light-matter interaction is included to describe the energy conversion in the devices under non-equilibrium condition. The reliability of our method is illustrated by numerical simulations of silicon nanowire based solar cells and LED devices. EL spectra of the nanowire under different bias voltage are obtained and, more importantly, radiation pattern and polarization of optical emission can be determined using our approach. Our work is a step forward towards atomistic quantum mechanical modeling of light-induced current and electrically induced optical response in nanoscale system. Moreover, a novel quantum theory is developed to describe the energy conversion of plasmonic hot-carrier solar cell, which is used to study the fundamental limitations to plasmonic hot-carrier solar cells. The numerical results indicate this cell can significantly improve the absorption of solar radiation but it suffers from low internal quantum efficiency as plasmon excitation creates a broad distribution of hot electron/hole energies. The connection of these results to recent experiments will also be described.

Yu Zhang is currently a Postdoctoral Fellow in Department of Chemistry and Center for Bio-inspired Energy Science at the Northwestern University, working for Prof. George C. Schatz. He hold a BSc in Physics from Sun Yat-Sen University in 2010, where he did undergraduate researches on quantum optics. In 2014, He finished his PhD study in Chemical Physics under the supervision of Prof. GuanHua Chen in the Department of Chemistry and Center of Theoretical and Computational Physics at The University of Hong Kong. Yu Zhang is interested in the development and application of theoretical models and computational methods for problems of scientific importance. His researches are broadly categorized under theoretical condensed matter physics, chemical physics and biophysics. His current researches include quantum plasmonics, energy and charge transfer, hot-carrier relaxation and trapping, ion transport and pump, etc.