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Persistent Quantum Coherence and Strong Coupling Enable Fast Electron Transfer across the CdS/TiO2 Interface: A Time-Domain ab Initio Simulation

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journal contribution
posted on 16.10.2018, 00:00 by Hamid Mehdipour, Alexey V. Akimov, Joanna Jankowska, Ali T. Rezakhanai, Saeedeh S. Tafreshi, Nora H. de Leeuw, Alireza Z. Moshfegh, Oleg V. Prezhdo
Fast transfer of photoinduced electrons and subsequent slow electron–hole recombination in semiconductor heterostructures give rise to long-lived charge separation which is highly desirable for photocatalysis and photovoltaic applications. As a type II heterostructure, CdS/TiO2 nanocomposites extend the absorption edge of the light spectrum to the visible range and demonstrate effective charge separation, resulting in more efficient conversion of solar energy to chemical energy. This improvement in performance is partly explained by the fact that CdS/TiO2 is a type II semiconductor heterostructure and CdS has a smaller energy band gap than UV-active TiO2. Ultrafast transient absorption measurements have revealed that electrons generated in CdS by visible light can quickly transfer into TiO2 before recombination takes place within CdS. Here, using time-domain density functional theory and nonadiabatic molecular dynamics simulations, we show how electronic subsystems of the CdS and TiO2 semiconductors are coupled to their lattice vibrations and coherently evolve, enabling effective transfer of photoinduced electrons from CdS into TiO2. This very fast electron transfer, and subsequent slow recombination of the transferred electrons with the holes left in CdS, is verified experimentally through the proven efficient performance of CdS/TiO2 heterostructures in photocatalysis and photovoltaic applications.