中文摘要：

为了实现窄能隙有机光敏剂的理性设计,有必要全面理解发生在二氧化钛/染料/电解质复杂界面的激发态演化动力学。本文通过构建分别以苯并噻二唑-苯甲酸（BTBA）和吡啶并噻二唑-苯甲酸（PTBA）为电子受体的有机给受体染料,借助超快瞬态吸收光谱测量与理论模拟,我们发现在实际的二氧化钛/染料/电解质界面存在激发态多步弛豫与多态电子注入的过程。密度泛函理论及含时密度泛函理论计算表明,二氧化钛表面的光激发产生的“热”激发态染料分子会通过分子片段间的扭转运动发生显著的多步结构弛豫,最终形成共轭骨架具有醌式结构、更加平面化的平衡构型。通过对飞秒瞬态吸收光谱进行目标分析,我们发现相对于以苯并噻二唑-苯甲酸为电子受体的染料,以吡啶并噻二唑-苯甲酸为电子受体的染料呈现出较慢的电子注入速率与较短的激发态寿命,导致总的电子注入产率较低,给出了基于该染料所制备的太阳电池的外量子产率峰值低的原因。

英文摘要：

Unlocking the dynamics of the evolution of the excited state at the complicated titania/dye/ electrolyte interface in organic dye-sensitized solar cells is crucial to provide a basis for the rational design of low-energy-gap organic photosensitizers. By constructing two organic donor-acceptor dyes composed of benzothiadiazole-benzoic acid （BTBA） and pyridothiadiazole-benzoic acid （PTBA） as electron acceptors, we have identified the images of multiple-step relaxations of the excited state and multiple-state electron injections at the titania/dye/electrolyte interface using ultrafast transient absorption spectroscopic measurements in conjunction with theoretical simulations. Density functional theory and time-dependent density functional theory calculations indicate that there should be torsion-induced excited state relaxations from an optically generated ＂hot＂ excited state to the equilibrium excited state characteristic of a more planar conjugated backbone and a quinonoid structure for dye molecules on the titania surface, suggesting the probable presence of multiple-state electron injections at the titania/dye/electrolyte interface. In virtue of a target analysis of femtosecond transient absorption spectra, we have found that the dye with PTBA features a much lower overall electron injection yield with respect to the dye with BTBA owing to the sluggish electron injection and short lifetime of the excited state, accounting for a lower maximum of external quantum efficiencies of the device made from the dye with PTBA as an acceptor.