Yang Yating, Fang Wei-Hai, Long Run
College of Chemistry, Key Laboratory of Theoretical & Computational Photochemistry of Ministry of Education, Beijing Normal University , Beijing 100875, People's Republic of China.
J Phys Chem Lett. 2017 Dec 7;8(23):5771-5778. doi: 10.1021/acs.jpclett.7b02779. Epub 2017 Nov 14.
Two-dimensional transition metal dichalcogenides (TMDs) heterojunctions are appealing candidates for optoelectronics and photovoltaics. Using time-domain density functional theory combined with nonadiabatic (NA) molecular dynamics, we show that photoexcitation dynamics exhibit a significant difference in the vertical and lateral MoS/WSe heterojunctions arising from the disparity in the donor-acceptor interaction and fundamental band alignment. The obtained electron transfer time scale in the vertical heterojunction shows excellent agreement with experiment. Hole transfer proceeds 1.5 times slower. The electron-hole recombination is 3 orders of magnitude longer than the charge separation, which favors solar cell applications. On the contrary, the lateral heterojunction shows no band offsets steering charge separation. The excited electron is localized at the interface that attracts holes to form an exciton-like state due to Coulomb interaction, suggesting potential applications in light-emitting devices. The coupled electron and hole wave functions increase NA coupling and the coherence time, accelerating electron-hole recombination by a factor of 3 compared with the vertical case. The atomistic studies advance our understanding of the photoinduced charge-phonon dynamics in TMDs heterojunctions.
二维过渡金属二硫属化物（TMDs）异质结是光电器件和光伏领域颇具吸引力的候选材料。通过结合时域密度泛函理论和非绝热（NA）分子动力学，我们发现，由于供体 - 受体相互作用和基本能带排列的差异，光激发动力学在垂直和横向MoS/WSe异质结中表现出显著差异。在垂直异质结中获得的电子转移时间尺度与实验结果高度吻合。空穴转移速度慢1.5倍。电子 - 空穴复合时间比电荷分离时间长3个数量级，这有利于太阳能电池应用。相反，横向异质结没有能带偏移来引导电荷分离。受激电子局限于界面处，由于库仑相互作用，该界面吸引空穴形成类激子态，这表明其在发光器件中有潜在应用。耦合的电子和空穴波函数增加了NA耦合和相干时间，与垂直情况相比，电子 - 空穴复合速度加快了3倍。这些原子尺度的研究加深了我们对TMDs异质结中光致电荷 - 声子动力学的理解。
