Department of Chemistry and ‡Department of Materials Science and Engineering, Northwestern University , Evanston, Illinois 60208, United States.
Nano Lett. 2017 Jan 11;17(1):164-169. doi: 10.1021/acs.nanolett.6b03704. Epub 2016 Dec 8.
van der Waals heterojunctions between two-dimensional (2D) layered materials and nanomaterials of different dimensions present unique opportunities for gate-tunable optoelectronic devices. Mixed-dimensional p-n heterojunction diodes, such as p-type pentacene (0D) and n-type monolayer MoS (2D), are especially interesting for photovoltaic applications where the absorption cross-section and charge transfer processes can be tailored by rational selection from the vast library of organic molecules and 2D materials. Here, we study the kinetics of excited carriers in pentacene-MoS p-n type-II heterojunctions by transient absorption spectroscopy. These measurements show that the dissociation of MoS excitons occurs by hole transfer to pentacene on the time scale of 6.7 ps. In addition, the charge-separated state lives for 5.1 ns, up to an order of magnitude longer than the recombination lifetimes from previously reported 2D material heterojunctions. By studying the fractional amplitudes of the MoS decay processes, the hole transfer yield from MoS to pentacene is found to be ∼50%, with the remaining holes undergoing trapping due to surface defects. Overall, the ultrafast charge transfer and long-lived charge-separated state in pentacene-MoS p-n heterojunctions suggest significant promise for mixed-dimensional van der Waals heterostructures in photovoltaics, photodetectors, and related optoelectronic technologies.
二维（2D）层状材料和不同维度纳米材料之间的范德华异质结为栅极可调谐光电设备提供了独特的机会。混合维度 p-n 异质结二极管，如 p 型并五苯（0D）和 n 型单层 MoS（2D），对于光伏应用特别有趣，因为可以通过从大量有机分子和 2D 材料库中进行合理选择来调整吸收截面和电荷转移过程。在这里，我们通过瞬态吸收光谱研究了并五苯-MoS p-n 型 II 异质结中激发载流子的动力学。这些测量表明，MoS 激子的解离是通过空穴转移到并五苯上发生的，时间尺度为 6.7 ps。此外，电荷分离态的寿命为 5.1 ns，比以前报道的二维材料异质结的复合寿命长一个数量级。通过研究 MoS 衰减过程的分数幅度，发现 MoS 向并五苯的空穴转移产率约为 50%，其余空穴由于表面缺陷而发生捕获。总体而言，在并五苯-MoS p-n 异质结中超快的电荷转移和长寿命的电荷分离态表明混合维度范德华异质结构在光伏、光电探测器和相关光电子技术中有很大的应用前景。
