The dynamics and efficiency of photoinduced electron transfer were measured at dye-sensitized photoanodes in aqueous (acetate buffer), nonaqueous (acetonitrile), and mixed solvent electrolytes by nanosecond transient spectroscopy (TAS) and ultrafast optical-pump terahertz-probe spectroscopy (OPTP). Higher injection efficiencies were found in mixed solvent electrolytes for dye-sensitized SnO2/TiO2 core/shell electrodes, whereas the injection efficiency of dye-sensitized TiO2 electrodes decreased with the increasing acetonitrile concentration. The trend in injection efficiency for the TiO2 electrodes was consistent with the solvent-dependent trend in the semiconductor flat-band potential. Photoinduced electron injection in core-shell electrodes has been understood as a two-step process involving ultrafast electron trapping in the TiO2 shell followed by slower electron transfer to the SnO2 core. The driving force for shell-to-core electron transfer increases as the flat band potential of TiO2 shifts negatively with increasing concentration of acetonitrile. In acetonitrile-rich electrolytes, despite the larger driving force, electron injection is suppressed. Interestingly, a net negative photoconductivity in the SnO2 core is observed in mixed solvent electrolytes by OPTP. We hypothesize that an electric field is formed across the TiO2 shell from the oxidized dye molecules after injection. The intrinsic conduction band electrons in SnO2 are trapped at the core-shell interface by the electric field, resulting in a negative photoconductivity transient. The overall electron injection efficiency of the dye- sensitized SnO2/TiO2 core/shell photoanodes, measured on longer timescales, is optimized in mixed solvents. The ultrafast transient conductivity data illustrate the crucial role of the electrolyte in regulating the driving forces for electron injection and charge separation at dye-sensitized semiconductor interfaces.

中文翻译：

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水/非水电解质混合物中染料敏化 SnO2/TiO2 核壳电极的电子转移动力学

通过纳秒瞬态光谱 (TAS) 和超快光泵太赫兹探针光谱 (OPTP) 在水性（醋酸盐缓冲液）、非水性（乙腈）和混合溶剂电解质中的染料敏化光阳极测量光诱导电子转移的动力学和效率。染料敏化 SnO2/TiO2 核/壳电极的混合溶剂电解质具有较高的注入效率，而染料敏化 TiO2 电极的注入效率随着乙腈浓度的增加而降低。 TiO2 电极的注入效率趋势与半导体平带电势的溶剂依赖性趋势一致。核壳电极中的光致电子注入被理解为一个两步过程，涉及 TiO2 壳中的超快电子捕获，然后较慢的电子转移到 SnO2 核。随着乙腈浓度的增加，TiO2 的平带电位负移，壳到核电子转移的驱动力增加。在富含乙腈的电解质中，尽管驱动力较大，但电子注入受到抑制。有趣的是，通过 OPTP 在混合溶剂电解质中观察到 SnO2 核中的净负光电导性。我们假设注射后氧化染料分子在 TiO2 壳上形成电场。 SnO2 中的本征导带电子被电场捕获在核壳界面，导致负光电导瞬态。在较长时间尺度上测量的染料敏化 SnO2/TiO2 核/壳光阳极的整体电子注入效率在混合溶剂中进行了优化。超快瞬态电导率数据说明了电解质在调节染料敏化半导体界面的电子注入和电荷分离驱动力方面的关键作用。