QUANTUM DYNAMICS OF EXCITED CHARGE CARRIER AT HETEROGENEOUS INTERFACE BETWEEN SEMICONDUCTOR AND ORGANIC MOLECULE Public Deposited

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  • March 21, 2019
Creator
  • Li, Lesheng
    • Affiliation: College of Arts and Sciences, Department of Chemistry
Abstract
  • Developing a quantitative understanding of excited charge carrier dynamics at heterogeneous interfaces between semiconductor and organic molecules is of great practical importance in advanced technologically important applications. Despite great advances in this field, there remain many aspects that are yet to be understood such as the density of charge carrier, the role of defects, and the interactions with surface ligand. To this end, we aim to develop and apply a quantitative formulation based on first-principles quantum theory to elucidate how excited carrier dynamics at semiconductor-molecule interfaces depend on the atomistic details. In this work, we systematically investigated several aspects of excited carrier dynamics at semiconductor-molecule interfaces via first-principles quantum mechanics simulations that are synergistically combined with the fewest-switches surface hopping algorithm, G0W0 many-body perturbation theory calculations, and first-principles molecular dynamics. We conclude that hot electron transfer to chemisorbed molecules was observed but was short-lived on the molecules. Interfacial electron transfer was found to be largely decoupled from hot electron relaxation within the semiconductor. While hot electron relaxation was found to take place on a time scale of several hundred femtoseconds, the subsequent interfacial electron transfer was slower by an order of magnitude. Meanwhile, this secondary process of picosecond electron transfer was found to be comparable in time scale to typical electron trapping into defect states in the energy gap. We then investigated how molecular details such as surface coverage and adsorbate species influence hot electron transfer. Counterintuitively, increasing surface coverage was found to suppress hot electron transfer probability because the increased delocalization of the hot electron accepting molecular states change the nonadiabatic couplings at the interface. In addition, the adsorbate species itself is an important factor in hot electron transfer not simply because of energy level alignments, but because the transfer is quite sensitive to nonadiabatic couplings. Finally, we examined the extent to which exchange-correlation approximations influence the interfacial charge transfer at a representative heterogeneous interface. We showed how the charge transfer kinetics are influenced by the exchange-correlation approximation through lattice movement, nonadiabatic couplings, and energy level alignments. The interfacial electron transfer time scale was found to vary by as much as, but not more than, one order of magnitude.
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Advisor
  • Berkowitz, Max
  • Dempsey, Jillian
  • Atkin, Joanna
  • Cahoon, James
  • Kanai, Yosuke
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2018
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