Abstract Low-bandgap conjugated polymers, which have an alternating structure of electron-donating and electron-withdrawing monomer units in their main chains, are expected to show high photovoltaic efficiency when the monomer units are appropriately designed. For understanding key factors of the photovoltaic efficiency, we have investigated the structure and dynamics of short-lived transients in films of a low-bandgap conjugated polymer with an alternating structure of thieno[3,4-b]thiophene and benzo[1,2-b:4,5-b′]dithiophene, PTB7, by time-resolved near-infrared stimulated Raman spectroscopy as well as time-resolved near-infrared absorption spectroscopy. Positive polarons of PTB7 are clearly distinguished from its singlet excitons in stimulated Raman spectra by the peak position of a CC stretch band of the thiophene rings in benzodithiophene and intensity of a C S C deformation band of them. These differences strongly suggest that the repeated structure of thiophene rings in the main chain predominantly contributes to the charge transfer characteristics of PTB7 in films. Time-resolved absorption and stimulated Raman spectra of PTB7 films blended with a fullerene derivative show that spectral changes associated with the initial charge separation complete within 1 ps while effects of conformational changes and intermediate species are absent. We suggest that alternating copolymers composed of electron-donating and electron-accepting units commonly undergo the initial charge separation process without conformational changes or intermediates.

中文翻译：

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近红外共振刺激拉曼研究 PTB7 薄膜中的短寿命瞬变

摘要 低带隙共轭聚合物在其主链上具有供电子和吸电子单体单元交替结构，当单体单元设计合理时，有望显示出较高的光伏效率。为了了解光伏效率的关键因素，我们研究了具有噻吩并 [3,4-b] 噻吩和苯并 [1,2] 交替结构的低带隙共轭聚合物薄膜中短寿命瞬变的结构和动力学-b:4,5-b']二噻吩，PTB7，通过时间分辨近红外受激拉曼光谱以及时间分辨近红外吸收光谱。通过苯并二噻吩中噻吩环的 CC 拉伸带的峰值位置和它们的 CSC 变形带的强度，PTB7 的正极化子与受激拉曼光谱中的单线态激子明显不同。这些差异强烈表明主链中噻吩环的重复结构主要有助于薄膜中 PTB7 的电荷转移特性。与富勒烯衍生物混合的 PTB7 薄膜的时间分辨吸收和受激拉曼光谱表明，与初始电荷分离相关的光谱变化在 1 ps 内完成，而没有构象变化和中间物种的影响。