共轭聚合物内非均匀场驱动的超快激子输运的动力学研究

Dynamical study of ultrafast exciton migration in coujugated polymers driven by nonuniform field

基于激子输运在聚合物给体/富勒烯(或非富勒烯)受体异质结太阳能电池光伏过程中的重要作用,本文结合最新的实验进展,从理论上提出了由非均匀场驱动的超快激子输运机制.动力学模拟采用扩展的一维Su-Schrieffer-Heeger紧束缚模型结合非绝热的量子动力学方法,而非均匀场主要考虑了由受限电荷诱导的非均匀电场和分子排列相关的非均匀构型场.研究发现:非均匀电场和构型场均可驱动激子实现超快输运,其输运速度比由传统的Forster或Dexter机制主导的激子输运可分别提高1和2个数量级.另外,本文重点分析了这两种非均匀场对激子输运的驱动机制,定量计算了它们各自诱导的驱动力.最后,针对影响这两种非均匀场分布的因素(包括受限电荷相对聚合物分子的距离和聚合物分子线性排列的斜率),讨论了它们对激子输运动力学的影响.

Due to the exciton migration dynamics playing an important role in the photovoltaic process of organic solar cells,which are usually composed of polymer donor and fullerene(or non-fullerene)acceptor,in this paper we propose a new strategy to achieve the ultrafast exciton migration in polymers.Here,the effects of some nonuniform fields on the exciton migration dynamics in polymers are emphasized,such as the nonuniform electric field and the nonuniform polymer packing configuration field.Both of the two kinds of nonuniform fields can be intrinsically existent or modulated in an actual photovoltaic system.In this work,the nonuniform electric field and the nonuniform configuration field are assumed to be separately created by a confined charge and a linear polymer packing,therefore,their model Hamiltonian is established.In dynamical simulations of the exciton migration dynamics in polymers,an extended version of one-dimensional Su-Schrieffer-Heeger tightbinding model combined with a nonadiabatic evolution method is employed.It is found that the nonuniform electric field and the nonuniform configuration field both can drive exciton to an ultrafast migration process.Compared with the exciton migration speed dominated by the traditional Forster or Dexter mechanism,the exciton migration speed dominated by the nonuniform electric field and that by the nonuniform configuration field can be increased by one and two orders of magnitude,respectively.In addition,the driving mechanisms of the two kinds of nonuniform fields for the exciton migration dynamics are separately clarified,where the corresponding driving forces are also quantitatively calculated.Finally,in view of the factors affecting the distributions of the two kinds of nonuniform fields(such as the distance d between confined charge and polymer,and the linear packing slope k between polymers),we discuss their effects on the exciton migration dynamics.It is found that the exciton migration in polymer can be apparently accelerated by shortening the distance d between confined charge and polymer,and there exists a critical value of d,beyond which the exciton will be dissociated into free charges in its migration process.For the linear packing slope k between polymers,we find that there exists an optimal value,at which the excit.on has the highest migration speed in polymers.