Institut für Physikalische und Theoretische Chemie, Universität Würzburg , Emil-Fischer-Str. 42, 97074 Würzburg, Germany.
J Am Chem Soc. 2014 Jul 2;136(26):9327-37. doi: 10.1021/ja413115h. Epub 2014 Jun 19.
The exciton diffusion length (LD) is a key parameter for the efficiency of organic optoelectronic devices. Its limitation to the nm length scale causes the need of complex bulk-heterojunction solar cells incorporating difficulties in long-term stability and reproducibility. A comprehensive model providing an atomistic understanding of processes that limit exciton trasport is therefore highly desirable and will be proposed here for perylene-based materials. Our model is based on simulations with a hybrid approach which combines high-level ab initio computations for the part of the system directly involved in the described processes with a force field to include environmental effects. The adequacy of the model is shown by detailed comparison with available experimental results. The model indicates that the short exciton diffusion lengths of α-perylene tetracarboxylicdianhydride (PTCDA) are due to ultrafast relaxation processes of the optical excitation via intermolecular motions leading to a state from which further exciton diffusion is hampered. As the efficiency of this mechanism depends strongly on molecular arrangement and environment, the model explains the strong dependence of LD on the morphology of the materials, for example, the differences between α-PTCDA and diindenoperylene. Our findings indicate how relaxation processes can be diminished in perylene-based materials. This model can be generalized to other organic compounds.
激子扩散长度 (LD) 是有机光电设备效率的关键参数。其限制在纳米长度范围内导致需要复杂的体异质结太阳能电池，这在长期稳定性和重现性方面带来了困难。因此，非常需要提供一种对限制激子输运过程的原子理解的综合模型，这里将为基于苝的材料提出这样的模型。我们的模型基于使用混合方法的模拟，该方法将直接参与描述过程的系统部分的高级从头计算与力场相结合，以包括环境影响。通过与可用实验结果的详细比较，证明了该模型的充分性。该模型表明，α-苝四羧酸二酐 (PTCDA) 的短激子扩散长度是由于光激发通过分子间运动发生超快弛豫过程，导致进一步的激子扩散受到阻碍的状态。由于这种机制的效率强烈依赖于分子排列和环境，该模型解释了 LD 对材料形态的强烈依赖性，例如 α-PTCDA 和二茚并苝之间的差异。我们的研究结果表明如何减少基于苝的材料中的弛豫过程。该模型可以推广到其他有机化合物。
