Dynamics of charge recombination at surface observed by highly sensitive transient absorption spectrometer

界面电荷复合是一个有趣的过程，它已被应用于太阳能转换装置，如光催化剂和染料敏化太阳能电池。光激发发生电荷分离，然后产生阳离子和阴离子。这些是非发射物种，因此这些物种的动力学不能用荧光光谱探测。瞬态吸收技术是研究这一目标的有力工具。然而，在现实中，由于灵敏度低，探测这些现象是相当困难的。为此，我们提出研制高灵敏度瞬态吸收光谱仪。首先，研制了高灵敏度瞬态吸收光谱仪。使用光谱仪，我们可以观察到非常小的吸光度变化（<10^<-6>）。这一灵敏度足以观察单层薄膜中的瞬态吸收。研究了染料敏化半导体薄膜的电荷分离和复合动力学，有机染料吸附在氧化物半导体（TiO_2,ZnO， SnO_2等）上。我们发现电荷分离的量子产率对激发光强非常敏感，在较低的激发光强下量子产率保持恒定。我们还估计了电荷分离的绝对量子产率。我们还研究了TiO_2薄膜等光催化剂的主要光激发过程。光激发产生电子和空穴。利用我们的光谱仪可以研究这些物质的反应性。

Charge recombination at interface is an interesting process and it has been applied to solar energy conversion devices, such as photocatalysts and dye-sensitized solar cells. Upon photoexcitation charge separation occurs and then cations and anions are produced. These are non-emitive species and therefore dynamics of these species cannot be probed by fluorescence spectroscopy. Transient absorption technique is a powerful tool for this target. However, in reality it is quite difficult to probe these phenomena due to low sensitivity. Thus, we proposed to develop highly sensitive transient absorption spectrometer.Firstly, we developed highly sensitive transient absorption spectrometer. Using the spectrometer, we can observed very small absorbance change (<10^<-6>). This is enough sensitivity to observe transient absorption in mono-layer film.We studied charge separation and recombination dynamics of dye-sensitized semiconductor films, organic dyes adsorbed on oxide semiconductors (TiO_2,ZnO, SnO_2 etc.). We found that quantum yield of the charge separation is very sensitive to the exciting light intensity and it becomes constant at lower intensity. We also estimated absolute quantum yield of the charge separation. We also studied primary process of photoexcitation of photocatalyst, such as TiO_2 films. Upon photoexcitation electrons and holes are produced. Using our spectrometer reactivity of these species can be studied.