McCool Nicholas S, Swierk John R, Nemes Coleen T, Schmuttenmaer Charles A, Mallouk Thomas E
Department of Chemistry and Energy Sciences Institute, Yale University , 225 Prospect Street, P.O. Box 208107, New Haven, Connecticut 06520-8107, United States.
J Phys Chem Lett. 2016 Aug 4;7(15):2930-4. doi: 10.1021/acs.jpclett.6b01528. Epub 2016 Jul 19.
Water-splitting dye-sensitized photoelectrochemical cells (WS-DSPECs) rely on photoinduced charge separation at a dye/semiconductor interface to supply electrons and holes for water splitting. To improve the efficiency of charge separation and reduce charge recombination in these devices, it is possible to use core/shell structures in which photoinduced electron transfer occurs stepwise through a series of progressively more positive acceptor states. Here, we use steady-state emission studies and time-resolved terahertz spectroscopy to follow the dynamics of electron injection from a photoexcited ruthenium polypyridyl dye as a function of the TiO2 shell thickness on SnO2 nanoparticles. Electron injection proceeds directly into the SnO2 core when the thickness of the TiO2 shell is less than 5 Å. For thicker shells, electrons are injected into the TiO2 shell and trapped, and are then released into the SnO2 core on a time scale of hundreds of picoseconds. As the TiO2 shell increases in thickness, the probability of electron trapping in nonmobile states within the shell increases. Conduction band electrons in the TiO2 shell and the SnO2 core can be differentiated on the basis of their mobility. These observations help explain the observation of an optimum shell thickness for core/shell water-splitting electrodes.
光解水染料敏化光电化学电池（WS-DSPEC）依靠染料/半导体界面处的光致电荷分离来为水分解提供电子和空穴。为了提高这些器件中的电荷分离效率并减少电荷复合，可以使用核/壳结构，其中光致电子转移通过一系列逐渐更正的受体态逐步发生。在此，我们使用稳态发射研究和时间分辨太赫兹光谱来跟踪从光激发的钌多吡啶染料注入电子的动力学，该动力学是关于SnO2纳米颗粒上TiO2壳层厚度的函数。当TiO2壳层厚度小于5埃时，电子直接注入SnO2核中。对于更厚的壳层，电子注入到TiO2壳层中并被捕获，然后在数百皮秒的时间尺度上释放到SnO2核中。随着TiO2壳层厚度的增加，电子被困在壳层内非移动态的概率增加。TiO2壳层和SnO2核中的导带电子可以根据它们的迁移率来区分。这些观察结果有助于解释核/壳光解水电极存在最佳壳层厚度的现象。
