Bombile Joel H, Shetty Shreya, Janik Michael J, Milner Scott T
Pennsylvania State University, University Park, PA 16802, USA.
Phys Chem Chem Phys. 2020 Feb 19;22(7):4032-4042. doi: 10.1039/c9cp06039a.
Conjugated polymers are potential next-generation materials for organic electronic devices. The ability of these materials to transport charges is a key factor limiting their performance. Charge carriers in conjugated polymers are localized by disorder and polaronic effects. Charge transport in these materials is often described by thermally activated hopping, with a rate given by Marcus theory. The polaron hopping activation energy determines the temperature dependence of the Marcus rate. This energy barrier is dictated by the transition state, in which the charge carrier is equally divided between the initial and final locations. The prefactor for the polaron hopping rate is set by the charge tunneling rate between the initial and final locations. We use a tight-binding polaron model, in which charge carriers are stabilized by both nuclear reorganization and polarization of the surrounding dielectric, to compute the activation energy, charge tunneling rate and overall rate constant for intrachain and interchain charge hopping processes in poly(3-hexylthiophene) (P3HT) crystalline lamellae and amorphous melts. Charge transport in these two environments is limited by interchain hopping processes. Both hopping barriers and rates predicted by the model are in good agreement with experiments on a variety of crystalline and amorphous P3HT materials. Qualitatively, the barriers largely depend on how well the transition state is stabilized by polarization effects, and on the hopping integral between the initial and final locations, both of which penalize hopping over longer distances.
共轭聚合物是有机电子器件潜在的下一代材料。这些材料的电荷传输能力是限制其性能的关键因素。共轭聚合物中的电荷载流子会因无序和极化子效应而局域化。这些材料中的电荷传输通常用热激活跳跃来描述，其速率由马库斯理论给出。极化子跳跃激活能决定了马库斯速率的温度依赖性。这个能垒由过渡态决定，在过渡态中电荷载流子在初始位置和最终位置之间平均分配。极化子跳跃速率的前置因子由初始位置和最终位置之间的电荷隧穿速率确定。我们使用一个紧束缚极化子模型，其中电荷载流子通过核重排和周围电介质的极化而稳定，来计算聚（3 - 己基噻吩）（P3HT）晶体薄片和非晶熔体中链内和链间电荷跳跃过程的激活能、电荷隧穿速率和总速率常数。这两种环境中的电荷传输受链间跳跃过程限制。该模型预测的跳跃势垒和速率与各种晶体和非晶P3HT材料的实验结果吻合良好。定性地说，势垒很大程度上取决于过渡态通过极化效应稳定的程度，以及初始位置和最终位置之间的跳跃积分，这两者都会阻碍长距离跳跃。
