Parameters influencing charge recombination kinetics in dye-sensitized nanocrystalline titanium dioxide films
Parameters influencing charge recombination kinetics in dye-sensitized nanocrystalline titanium dioxide films
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DOI：
10.1021/jp991085x
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发表时间：
2000-01-27
影响因子：
3.3
通讯作者：
Durrant, JR
中科院分区：
文献类型：
--
作者：
Haque, SA;Tachibana, Y;Durrant, JR
Ru-II（2,2‘-联吡啶-4,4’二羧酸酯）(2)(NCS)(2)敏化纳米TiO2薄膜的光激发导致电子注入半导体。本文讨论了电荷分离反应后的电荷重组动力学。这些电荷复合动力学被发现强烈地依赖于激发强度、电解质组成和对TiO2薄膜施加电偏置。当激发强度小于1个染料分子/TiO2粒子时，复合动力学与激发强度无关。在此水平上增加激发强度会导致电荷复合动力学的快速加速。同样，对于施加在TiO2电极上的正电位，复合动力学与施加电位无关。如果施加的电位比阈值电位V-kin更负，则再次观察到电荷重组动力学的快速加速，例如，从+0.1 V时的1 ms到-0.8 V时的3 ps（类似于10(8)倍的速率增加）。此外，在恒定的施加电位下，电荷重组动力学被发现强烈依赖于电解质组成（高达10(6)倍的速率变化）。这种对电解质组成的强烈依赖被发现与阈值电位V-kin的移位有关。光谱电化学测量用于监测由电解质组成引起的阱/导带密度的变化。在动力学测量中观察到的阈值电压V-kin与光谱电化学测量中观察到的TiO2的电子占据导带/阱态的阈值电压之间存在直接的相关性。这种直接相关性在广泛的电解质组成中被观察到，包括质子和非质子溶剂，以及Li+离子和4-叔丁基吡啶的添加。我们得出结论，在这种染料敏化薄膜中的电荷重组动力学强烈依赖于TiO2薄膜在陷阱/导带状态中的电子占据。这种作用可以通过光强度、外加电势和电解质组成的变化来调节。讨论了这些结果与染料敏化光电化学器件功能的关系。
Optical excitation of Ru-II(2,2'-bipyridyl-4,4'dicarboxylate)(2)(NCS)(2)-sensitized nanocrystalline TiO2 films results in injection of an electron into the semiconductor. This paper addresses the kinetics of charge recombination which follows this charge separation reaction. These charge recombination kinetics were found to be strongly dependent upon excitation intensity, electrolyte composition, and the application of an electrical bias to the TiO2 film. For excitation intensities resulting in less than one excited dye molecule/TiO2 particle, the recombination kinetics were independent of excitation intensity. Increasing the excitation intensity above this level resulted in a rapid acceleration in the charge recombination kinetics. Similarly, for positive electrical potentials applied to the TiO2 electrode, the recombination kinetics were independent of applied potential. If the applied potential was more negative than a threshold potential V-kin, a rapid acceleration of the charge recombination kinetics was again observed, for example from similar to 1 ms at +0.1 V vs Ag/AgCl to similar to 3 ps at -0.8 V (similar to 10(8) fold increase in the rate). Moreover, at a constant applied potential the charge recombination kinetics were found to be strongly dependent upon electrolyte composition (up to 10(6)-fold change in rate). This strong dependence upon the electrolyte composition was found to be associated with shifts in the threshold potential V-kin. Spectroelectrochemical measurements were used to monitor the shift in the trap/conduction band density of states induced by the electrolyte composition. A direct correlation was observed between the threshold voltage V-kin observed from kinetic measurements, and the threshold voltage for electron occupation of conduction band/trap states of the TiO2 observed from spectroelectrochemical measurements. This direct correlation was observed for a wide range of electrolyte compositions including protic and aprotic solvents and the addition of Li+ ions and 4-tert-butylpyridine. We conclude that the charge recombination kinetics in such dye-sensitized films are strongly dependent upon the electron occupation in trap/conduction band states of the TiO2 film. This occupation may be modulated by variations in light intensity, applied electrical potential, and electrolyte composition. These results are discussed with relevance to the function of dye-sensitized photoelectrochemical devices.