Shi Ya-Rui, Liu Yu-Fang
College of Physics and Electronic Engineering, Henan Normal University, Xinxiang, 453007, China.
Phys Chem Chem Phys. 2019 Jun 28;21(24):13304-13318. doi: 10.1039/c9cp02170a. Epub 2019 Jun 11.
The charge transfer process between substrate molecular and dopant always appears in doped organic semiconductors, so that molecular doping is a common method to improve the electrical properties by combining appropriate complexes of electron acceptor and donor molecules. At the interface of the doped complexes, the amount of charge-transfer based on the charge analysis method could be affected by various factors, including the stacking structure, the HOMO-LUMO gaps, the offset defined by the donor ionization potential and the acceptor electron affinity IP-|EA|, and the strength of the intermolecular orbital interaction. To better understand the charge transport properties in complex crystals, reasonable mobility values were calculated by combining semi-classical Marcus-Hush theory with molecular dynamics simulation, in which the mobility values were on the same order of magnitude as experimental values. The largest and average room-temperature mobility were 4.59 and 0.21 cm V s for TTF-TCNQ based on the anisotropic transport properties and random-walk schemes of the charge diffusion coefficient. The interface of the TTF-TCNQ crystal possesses metallic conducting properties with a predicted resistance of 4.43 kΩ. Charge-transfer complexes exhibit larger mobility and higher conductivity compared to the constituent donor and acceptor molecules.
在掺杂有机半导体中，底物分子与掺杂剂之间总会出现电荷转移过程，因此分子掺杂是通过结合合适的电子受体和供体分子复合物来改善电学性质的常用方法。在掺杂复合物的界面处，基于电荷分析方法的电荷转移量可能会受到多种因素的影响，包括堆积结构、HOMO-LUMO能隙、由供体电离势和受体电子亲和势IP-|EA|定义的偏移，以及分子间轨道相互作用的强度。为了更好地理解复合晶体中的电荷传输性质，通过将半经典Marcus-Hush理论与分子动力学模拟相结合来计算合理的迁移率值，其中迁移率值与实验值处于同一数量级。基于电荷扩散系数的各向异性传输性质和随机游走方案，TTF-TCNQ的最大室温迁移率和平均室温迁移率分别为4.59 cm² V⁻¹ s⁻¹和0.21 cm² V⁻¹ s⁻¹。TTF-TCNQ晶体的界面具有金属导电性质，预测电阻为4.43 kΩ。与组成的供体和受体分子相比，电荷转移复合物表现出更大的迁移率和更高的电导率。
