Département de Physique and Regroupement Québécois sur les Matériaux de Pointe, Université de Montréal, C.P. 6128, Succursale Centre-Ville, Montréal, Québec, Canada H3C 3J7.
Central Laser Facility, Research Complex at Harwell, Science and Technology Facilities Council, Rutherford Appleton Laboratory, Harwell Oxford, Didcot, Oxfordshire OX11 0QX, UK.
Nat Commun. 2014 Jul 1;5:4288. doi: 10.1038/ncomms5288.
In polymeric semiconductors, charge carriers are polarons, which means that the excess charge deforms the molecular structure of the polymer chain that hosts it. This results in distinctive signatures in the vibrational modes of the polymer. Here, we probe polaron photogeneration dynamics at polymer:fullerene heterojunctions by monitoring its time-resolved resonance-Raman spectrum following ultrafast photoexcitation. We conclude that polarons emerge within 300 fs. Surprisingly, further structural evolution on ≲ 50-ps timescales is modest, indicating that the polymer conformation hosting nascent polarons is not significantly different from that near equilibrium. We interpret this as suggestive that charges are free from their mutual Coulomb potential because we would expect rich vibrational dynamics associated with charge-pair relaxation. We address current debates on the photocarrier generation mechanism at molecular heterojunctions, and our work is, to our knowledge, the first direct probe of molecular conformation dynamics during this fundamentally important process in these materials.
在聚合物半导体中，载流子是极化子，这意味着过剩电荷会使承载它的聚合物链的分子结构发生变形。这导致聚合物振动模式中出现独特的特征。在这里，我们通过监测超快光激发后聚合物：富勒烯异质结的时间分辨共振拉曼光谱来探测极化子光生动力学。我们得出结论，极化子在 300fs 内出现。令人惊讶的是，在 ≲ 50-ps 时间尺度上进一步的结构演化是适度的，这表明承载新生极化子的聚合物构象与平衡态附近的构象没有显著差异。我们将这解释为电荷不受其库仑势的影响，因为我们预计与电荷对弛豫相关的丰富的振动动力学。我们解决了分子异质结上光生载流子产生机制的当前争议，并且据我们所知，我们的工作是首次直接探测这些材料中这一基本过程中分子构象动力学。
