Department of Polymer Science, University of Akron, Akron, Ohio 44325, USA.
J Chem Phys. 2012 Jul 7;137(1):014903. doi: 10.1063/1.4731698.
A general dynamic Monte Carlo model for exciton dissociation at a donor-acceptor interface that includes exciton delocalization and hot charge separation is developed to model the experimental behavior observed for the poly(3-hexylthiophene):fullerene system and predict the theoretical performance of future materials systems. The presence of delocalized excitons and the direct formation of separated charge pairs has been recently measured by transient photo-induced absorption experiments and has been proposed to facilitate charge separation. The excess energy of the exciton dissociation process has also been observed to have a strong correlation with the charge separation yield for a series of thiophene based polymer:fullerene systems, suggesting that a hot charge separation process is also occurring. Hot charge separation has been previously theorized as a cause for highly efficient charge separation. However, a detailed model for this process has not been implemented and tested. Here, both conceptual models are implemented into a dynamic Monte Carlo simulation and tested using a simple bilayer donor-acceptor system. We find that exciton delocalization can account for a significant reduction in geminate recombination when compared to the traditional, bound polaron pair model. In addition, the hot charge separation process could further reduce the geminate recombination, but only if the hot charge mobility is several orders of magnitude larger than the standard charge mobility.
我们开发了一种通用的动态蒙特卡罗模型，用于模拟施主-受主界面处激子的解离，该模型考虑了激子离域和热电荷分离，可以模拟聚（3-己基噻吩）：富勒烯体系的实验行为，并预测未来材料体系的理论性能。最近通过瞬态光致吸收实验测量到了离域激子和分离电荷对的直接形成，并提出这有助于电荷分离。对于一系列噻吩基聚合物：富勒烯体系，激子解离过程中的过剩能量也与电荷分离产率具有很强的相关性，这表明也发生了热电荷分离过程。热电荷分离之前被认为是高效电荷分离的原因。然而，对于这个过程还没有实施和测试详细的模型。在这里，我们将这两个概念模型都实现到动态蒙特卡罗模拟中，并使用简单的双层施主-受主体系进行了测试。我们发现，与传统的束缚极化子对模型相比，激子离域可以显著降低复合几率。此外，热电荷分离过程可以进一步降低复合几率，但前提是热电荷迁移率比标准电荷迁移率大几个数量级。
