Van der Waals-coupled two-dimensional (2D) heterostructures have attracted great attention recently due to their high potential in the next-generation photodetectors and solar cells. The understanding of charge-transfer process between adjacent atomic layers is the key to design optimal devices as it directly determines the fundamental response speed and photon-electron conversion efficiency. However, general belief and theoretical studies have shown that the charge transfer behavior depends sensitively on interlayer configurations, which is difficult to control accurately, bringing great uncertainties in device designing. Here we investigate the ultrafast dynamics of interlayer charge transfer in a prototype heterostructure, the MoS₂/WS₂ bilayer with various stacking configurations, by optical two-color ultrafast pump–probe spectroscopy. Surprisingly, we found that the charge transfer is robust against varying interlayer twist angles and interlayer coupling strength, in time scale of ∼90 fs. Our observation, together with atomic-resolved transmission electron characterization and time-dependent density functional theory simulations, reveals that the robust ultrafast charge transfer is attributed to the heterogeneous interlayer stretching/sliding, which provides additional channels for efficient charge transfer previously unknown. Our results elucidate the origin of transfer rate robustness against interlayer stacking configurations in optical devices based on 2D heterostructures, facilitating their applications in ultrafast and high-efficient optoelectronic and photovoltaic devices in the near future.

中文翻译：

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MoS ₂ / WS ₂双层中可靠的独立于堆叠的超快电荷转移

Van der Waals耦合的二维（2D）异质结构由于在下一代光电探测器和太阳能电池中的巨大潜力，近来备受关注。了解相邻原子层之间的电荷转移过程是设计最佳器件的关键，因为它直接决定了基本响应速度和光电子转换效率。然而，一般的信念和理论研究表明，电荷转移行为敏感地取决于层间结构，这很难精确控制，从而给器件设计带来了很大的不确定性。在这里，我们研究了原型异质结构MoS ₂ / WS ₂中层间电荷转移的超快动力学。通过光学双色超快泵浦-探针光谱技术，可形成具有各种堆叠配置的双层薄膜。出乎意料的是，我们发现电荷转移在约90 fs的时间范围内对变化的层间扭曲角和层间耦合强度具有鲁棒性。我们的观察，再加上原子分辨的透射电子表征和随时间变化的密度泛函理论模拟，揭示了鲁棒的超快电荷转移归因于异质层间拉伸/滑动，这为以前未知的有效电荷转移提供了额外的渠道。我们的结果阐明了基于2D异质结构的光学设备中针对层间堆叠配置的传输速率鲁棒性的起源，