Charge Recombination and Exciton Annihilation Reactions in Conjugated Polymer Blends
Charge Recombination and Exciton Annihilation Reactions in Conjugated Polymer Blends
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DOI：
10.1021/ja908046h
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发表时间：
2010-01-13
影响因子：
15
通讯作者：
Greenham, Neil C.
中科院分区：
文献类型：
--
作者：
Howard, Ian A.;Hodgkiss, Justin M.;Greenham, Neil C.
共轭聚合物薄膜中激发态之间的双分子相互作用是重要的，因为它们影响许多需要高激发密度的光电器件的效率。使用时间分辨光谱，我们测量的双分子相互作用的电荷，单重态激子，和三重态激子在紧密混合的聚芴共混物的带边偏移优化的光诱导电子转移。双分子电荷复合和三重态-三重态湮灭可以忽略不计，但激子-电荷相互作用是有效的。单重态激子被电荷湮灭的过程发生在皮秒的时间尺度上，并达到与电荷转移相当的速率。三重态激子湮灭电荷发生在纳秒的时间尺度。令人惊讶的情况下nongeminate电荷复合显示是由于有限的迁移率的载流子在异质结。因此，可以在共混物中保持极高的电荷对密度。不存在三重态-三重态湮灭是共混物形态中受限三重态扩散的结果。我们认为，双分子相互作用的速率和性质是由聚合物共混物中的随机激发分布和聚合物域之间的有限连接性决定的。基于这些假设的模型定量地解释了这些影响。我们的研究结果提供了一个全面的框架，了解纳米结构材料中的双分子复合和湮灭过程。
Bimolecular interactions between excitations in conjugated polymer thin films are important because they influence the efficiency of many optoelectronic devices that require high excitation densities. Using time-resolved optical spectroscopy, we measure the bimolecular interactions of charges, singlet excitons, and triplet excitons in intimately mixed polyfluorene blends with band-edge offsets optimized for photoinduced electron transfer. Bimolecular charge recombination and triplet-triplet annihilation are negligible, but exciton-charge interactions are efficient. The annihilation of singlet excitons by charges occurs on picosecond time-scales and reaches a rate equivalent to that of charge transfer. Triplet exciton annihilation by charges occurs on nanosecond time-scales. The surprising absence of nongeminate charge recombination is shown to be due to the limited mobility of charge carriers at the heterojunction. Therefore, extremely high densities of charge pairs can be maintained in the blend. The absence of triplet-triplet annihilation is a consequence of restricted triplet diffusion in the blend morphology. We suggest that the rate and nature of bimolecular interactions are determined by the stochastic excitation distribution in the polymer blend and the limited connectivity between the polymer domains. A model based on these assumptions quantitatively explains the effects. Our findings provide a comprehensive framework for understanding bimolecular recombination and annihilation processes in nanostructured materials.