Athanasopoulos Stavros, Hoffmann Sebastian T, Bässler Heinz, Köhler Anna, Beljonne David
†Laboratory of Chemistry of Novel Materials, University of Mons, B-7000 Mons, Belgium.
‡Experimental Physics II and Bayreuth Institute of Macromolecular Research (BIMF), Department of Physics, University of Bayreuth, Bayreuth D-95440, Germany.
J Phys Chem Lett. 2013 May 16;4(10):1694-700. doi: 10.1021/jz400480a. Epub 2013 May 3.
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 Förster 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.
在无序有机半导体中，激发态和电荷通过在非均匀展宽的态密度中跳跃来移动，从而在能量上弛豫（“光谱扩散”）。在低温下，输运可能在动力学上受阻，从而导致色散。在实验中，这种现象主要在三重态激发和电荷中观察到，而对于单重态激发尚未有报道。我们通过使用具有米勒 - 亚伯拉罕斯或福斯特型转移速率的晶格蒙特卡罗方法模拟温度依赖的光谱扩散，来探究这一现象的起源。我们的模拟结果与最近的荧光和磷光实验结果一致。我们表明，当可用跳跃位点的数量有限时，就会出现受阻从而色散的扩散。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，但在受限几何结构或稀释体系中的单重态也可能出现。当有更多的跳跃位点可用时，例如由于某些非晶聚合物薄膜中共轭增加导致三重态有更多跳跃位点，受阻情况就会消除。
