Goswami Tanmay, Bhatt Himanshu, Yadav Dharmendra Kumar, Ghosh Hirendra N
Institute of Nano Science and Technology, Knowledge City, Sector 81, SAS Nagar, Punjab-140306, India.
School of Chemical Sciences, National Institute of Science Education and Research (NISER), Bhubaneswar, Odisha 752050, India.
Nanoscale. 2025 Feb 27;17(9):5213-5221. doi: 10.1039/d4nr03874f.
The performance of an optoelectronic device is largely dependent on the light harvesting properties of the active material as well as the dynamic behaviour of the photoexcited charge carriers upon absorption of light. Recently, atomically thin two-dimensional transition metal dichalcogenides (2D TMDCs) have garnered attention as highly prospective materials for advanced ultrathin solar cells and other optoelectronic applications, owing to their strong interaction with electromagnetic radiation, substantial optical conductivity, and impressive charge carrier mobility. WSe is one such extremely promising solar energy material. It has absorption throughout the UV-Vis-NIR region with the existence of four excitonic features, just like MoS and WS. However, stability issues and the absence of any robust synthetic route limit their practical applications. Herein, we have successfully synthesized atomically thin stable WSe nanosheets using a very effective colloidal hot injection method and further studied the optical properties of this material using femtosecond transient absorption spectroscopy. We probed all four excitonic features of WSe spread throughout the visible region. The dynamics of the high-energy excitons were found to be distinctively slower when compared to their band edge counterparts, adding an additional advantage in optoelectronic applications. We delved further into the factors governing exciton dynamics within WSe, uncovering the strong influence of the electronic band structure. Importantly, our study highlights the importance of all four excitonic features in a 2D TMDC material, which emerge in the system irrespective of the excitation wavelength and influence each other.
光电器件的性能在很大程度上取决于活性材料的光捕获特性以及光吸收后光激发电荷载流子的动态行为。最近，原子级薄的二维过渡金属二硫属化物（2D TMDCs）作为先进超薄太阳能电池和其他光电器件应用的极具前景的材料而备受关注，这是由于它们与电磁辐射的强相互作用、可观的光导率以及令人印象深刻的电荷载流子迁移率。WSe就是这样一种极具前景的太阳能材料。它在紫外 - 可见 - 近红外区域都有吸收，存在四个激子特征，就像MoS和WS一样。然而，稳定性问题以及缺乏任何可靠的合成路线限制了它们的实际应用。在此，我们使用一种非常有效的胶体热注入方法成功合成了原子级薄的稳定WSe纳米片，并使用飞秒瞬态吸收光谱进一步研究了这种材料的光学性质。我们探测了遍布可见光区域的WSe的所有四个激子特征。结果发现，与带边激子相比，高能激子的动力学明显更慢，这在光电器件应用中增添了一个额外的优势。我们进一步深入研究了WSe内部激子动力学所涉及的因素，揭示了电子能带结构的强烈影响。重要的是，我们的研究突出了二维TMDC材料中所有四个激子特征的重要性，这些特征在系统中出现，与激发波长无关且相互影响。
