Identification of Ultrafast Relaxation Processes As a Major Reason for Inefficient Exciton Diffusion in Perylene-Based Organic Semiconductors,Journal of the American Chemical Society

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Identification of Ultrafast Relaxation Processes As a Major Reason for Inefficient Exciton Diffusion in Perylene-Based Organic Semiconductors
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2014-06-19 , DOI: 10.1021/ja413115h
Volker Settels ₁ , Alexander Schubert ₁ , Maxim Tafipolski ₁ , Wenlan Liu ₁ , Vera Stehr ₂ , Anna K. Topczak _{2,

3} , Jens Pflaum _{2,

3} , Carsten Deibel ₂ , Reinhold F. Fink ₁ , Volker Engel ₁ , Bernd Engels ₁

Affiliation

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.

中文翻译：

确定超快弛豫过程是苝基有机半导体中激子扩散效率低下的主要原因

激子扩散长度 (LD) 是有机光电器件效率的关键参数。其对纳米长度尺度的限制导致需要复杂的体异质结太阳能电池，并在长期稳定性和再现性方面存在困难。因此，非常需要一个全面的模型，该模型提供对限制激子传输过程的原子理解，并将在此处针对苝基材料提出。我们的模型基于混合方法的模拟，该方法将直接参与所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。模型的充分性通过与可用实验结果的详细比较来显示。该模型表明，α-苝四羧酸二酐 (PTCDA) 的激子扩散长度短是由于光激发的超快弛豫过程通过分子间运动导致激子进一步扩散受阻的状态。由于这种机制的效率在很大程度上取决于分子排列和环境，该模型解释了 LD 对材料形态的强烈依赖性，例如，α-PTCDA 和二茚茚之间的差异。我们的研究结果表明如何减少苝基材料的弛豫过程。该模型可以推广到其他有机化合物。

更新日期：2014-06-19

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