title: Quantum Coherence Facilitates Efficient Charge Separation at a MoS2/MoSe2 van der Waals Junction.
abstract: Two-dimensional transition metal dichalcogenides (MX2, M = Mo, W; X = S, Se) hold great potential in optoelectronics and photovoltaics. To achieve efficient light-to-electricity conversion, electron-hole pairs must dissociate into free charges. Coulomb interaction in MX2 often exceeds the charge transfer driving force, leading one to expect inefficient charge separation at a MX2 heterojunction. Experiments defy the expectation. Using time-domain density functional theory and nonadiabatic (NA) molecular dynamics, we show that quantum coherence and donor-acceptor delocalization facilitate rapid charge transfer at a MoS2/MoSe2 interface. The delocalization is larger for electron than hole, resulting in longer coherence and faster transfer. Stronger NA coupling and higher acceptor state density accelerate electron transfer further. Both electron and hole transfers are subpicosecond, which is in agreement with experiments. The transfers are promoted primarily by the out-of-plane Mo-X modes of the acceptors. Lighter S atoms, compared to Se, create larger NA coupling for electrons than holes. The relatively slow relaxation of the "hot" hole suggests long-distance bandlike transport, observed in organic photovoltaics. The electron-hole recombination is notably longer across the MoS2/MoSe2 interface than in isolated MoS2 and MoSe2, favoring long-lived charge separation. The atomistic, time-domain studies provide valuable insights into excitation dynamics in two-dimensional transition metal dichalcogenides.
authors.affiliation: College of Chemistry, Key Laboratory of Theoretical and Computational Photochemistry of Ministry of Education, Beijing Normal University , Beijing, 100875, People's Republic of China.|School of Physics and Complex and Adaptive Systems Lab, University College Dublin , Dublin 4, Ireland.
authors.forename: Run
authors.initials: R
authors.lastname: Long
authors.affiliation: Department of Chemistry, University of Southern California , Los Angeles, California 90089, United States.
authors.forename: Oleg V
authors.initials: OV
authors.lastname: Prezhdo
keywords: MoS2/MoSe2 van der Waals heterojunction; charge separation and recombination; nonadiabatic molecular dynamics; nonradiative relaxation; quantum coherence; time-domain density functional theory