Key Laboratory of Excited-State Materials of Zhejiang Province, Department of Chemistry, Zhejiang University, Hangzhou 310027, China.
ZJU-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou, Zhejiang 311200, China.
J Am Chem Soc. 2023 May 24;145(20):11227-11235. doi: 10.1021/jacs.3c01192. Epub 2023 May 9.
Whether and how an electron-hole pair at the donor-acceptor interface separates from their mutual Coulombic interaction has been a long-standing question for both fundamental interests and optoelectronic applications. This question is particularly interesting but yet to be unraveled in the emerging mixed-dimensional organic/2D semiconductor excitonic heterostructures where the Coulomb interaction is poorly screened. Here, by tracking the characteristic electroabsorption (Stark effect) signal from separated charges using transient absorption spectroscopy, we directly follow the electron-hole pair separation process in a model organic/2D heterostructure, vanadium oxide phthalocyanine/monolayer MoS. After sub-100 fs photoinduced interfacial electron transfer, we observe a barrier-less long-range electron-hole pair separation to free carriers within 1 ps by hot charge transfer exciton dissociation. Further experiment reveals the key role of the charge delocalization in organic layers sustained by the local crystallinity, while the inherent in-plane delocalization of the 2D semiconductor has a negligible contribution to charge pair separation. This study reconciles the seemingly contradicting charge transfer exciton emission and dissociation process and is important to the future development of efficient organic/2D semiconductor optoelectronic devices.
在给体-受体界面处的电子-空穴对是否以及如何与其库仑相互作用分离，这一直是基础研究和光电应用都非常感兴趣的问题。在新兴的混合维度有机/二维半导体激子异质结构中，这个问题尤其有趣，但尚未得到解决，因为在这种结构中库仑相互作用的屏蔽效果很差。在这里，我们通过瞬态吸收光谱跟踪分离电荷的特征电吸收（斯塔克效应）信号，直接跟踪模型有机/二维异质结构（氧化钒酞菁/单层 MoS）中电子-空穴对的分离过程。在 100fs 以下的光诱导界面电子转移后，我们观察到在 1ps 内通过热电荷转移激子解离，无势垒的长程电子-空穴对分离为自由载流子。进一步的实验表明，有机层中电荷离域的关键作用是由局部结晶度维持的，而二维半导体的固有面内离域对电荷对分离几乎没有贡献。这项研究调和了看似矛盾的电荷转移激子发射和解离过程，对高效有机/二维半导体光电设备的未来发展非常重要。
