To Hop or Not to Hop? Understanding the Temperature Dependence of Spectral Diffusion in Organic Semiconductors
To Hop or Not to Hop? Understanding the Temperature Dependence of Spectral Diffusion in Organic Semiconductors
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DOI：
10.1021/jz400480a
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发表时间：
2013-05-16
影响因子：
5.7
通讯作者：
Beljonne, David
中科院分区：
文献类型：
--
作者：
Athanasopoulos, Stavros;Hoffmann, Sebastian T.;Beljonne, David
在无序有机半导体中，激发态和电荷通过在不均匀加宽的态密度中跳跃来移动，从而能量弛豫（“光谱扩散”）。在低温下，运输可能会受到动力学阻碍，从而导致分散。实验上，这主要是在三重态激发和电荷中观察到的，而对于单重态激发尚未有报道。我们通过使用具有 Miller-Abrahams 或 Forster 类型传输率的晶格蒙特卡罗方法来模拟温度相关的光谱扩散，解决了这种现象的根源。我们的模拟与最近的荧光和磷光实验结果一致。我们表明，当可用的跳跃位点数量有限时，会出现受挫扩散，从而出现色散扩散。对于通过短程相互作用转移的三重态来说，这种情况经常发生，但也可能发生在受限几何形状或稀释系统中的单重态中。当更多的跳跃位点可用时，例如由于某些无定形聚合物薄膜中的共轭增加而导致三联体，沮丧感就会消失。
In disordered organic semiconductors, excited states and charges move by hopping in an inhomogeneously broadened density of states, thereby relaxing energetically ("spectral diffusion"). At low temperatures, transport can become kinetically frustrated and consequently dispersive. Experimentally, this is observed predominantly for triplet excitations and charges, and has not been reported for singlet excitations. We have addressed the origin of this phenomenon by simulating the temperature dependent spectral diffusion using a lattice Monte Carlo approach with either Miller-Abrahams or Forster type transfer rates. Our simulations are in agreement with recent fluorescence and phosphorescence experimental results. We show that frustrated and thus dispersive diffusion appears when the number of available hopping sites is limited. This is frequently the case for triplets that transfer by a short-range interaction, yet may also occur for singlets in restricted geometries or dilute systems. Frustration is lifted when more hopping sites become available, e.g., for triplets as a result of an increased conjugation in some amorphous polymer films.