Neppl Stefan, Mahl Johannes, Roth Friedrich, Mercurio Giuseppe, Zeng Guosong, Toma Francesca M, Huse Nils, Feulner Peter, Gessner Oliver
Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, United States.
Physics Department, Universität Hamburg and Center for Free-Electron Laser Science, 22761 Hamburg, Germany.
J Phys Chem Lett. 2021 Dec 16;12(49):11951-11959. doi: 10.1021/acs.jpclett.1c02648. Epub 2021 Dec 9.
A prerequisite for advancing hybrid solar light harvesting systems is a comprehensive understanding of the spatiotemporal dynamics of photoinduced interfacial charge separation. Here, we demonstrate access to this transient charge redistribution for a model hybrid system of nanoporous zinc oxide (ZnO) and ruthenium bipyridyl chromophores. The site-selective probing of the molecular electron donor and semiconductor acceptor by time-resolved X-ray photoemission provides direct insight into the depth distribution of the photoinjected electrons and their interaction with the local band structure on a nanometer length scale. Our results show that these electrons remain localized within less than 6 nm from the interface, due to enhanced downward band bending by the photoinjected charge carriers. This spatial confinement suggests that light-induced charge generation and transport in nanoscale ZnO photocatalytic devices proceeds predominantly within the defect-rich surface region, which may lead to enhanced surface recombination and explain their lower performance compared to titanium dioxide (TiO)-based systems.
推进混合太阳能光捕获系统的一个先决条件是全面了解光致界面电荷分离的时空动力学。在此，我们展示了对于纳米多孔氧化锌（ZnO）和钌联吡啶发色团的模型混合系统，能够获取这种瞬态电荷重新分布。通过时间分辨X射线光电子能谱对分子电子供体和半导体受体进行位点选择性探测，可直接洞察光注入电子的深度分布及其在纳米长度尺度上与局部能带结构的相互作用。我们的结果表明，由于光注入电荷载流子增强了向下的能带弯曲，这些电子保持在距界面小于6纳米的范围内局域化。这种空间限制表明，纳米级ZnO光催化器件中光诱导电荷的产生和传输主要在富含缺陷的表面区域内进行，这可能导致表面复合增强，并解释了它们与基于二氧化钛（TiO）的系统相比性能较低的原因。
