Quantum Coherence Facilitates Efficient Charge Separation at a MoS2/MoSe2 van der Waals Junction

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• 作者：Run Long ; Oleg V. Prezhdo
• 刊名：Nano Letters
• 出版年：2016
• 出版时间：March 9, 2016
• 年：2016
• 卷：16
• 期：3
• 页码：1996-2003
• 全文大小：497K
• ISSN：1530-6992

文摘

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.