Hourani Wael, Rahimi Khosrow, Botiz Ioan, Koch Felix Peter Vinzenz, Reiter Günter, Lienerth Peter, Heiser Thomas, Bubendorff Jean-Luc, Simon Laurent
Institut de Science des Matériaux de Mulhouse (IS2M), Mulhouse, France.
Nanoscale. 2014 May 7;6(9):4774-80. doi: 10.1039/c3nr05858a.
The electronic properties of organic semiconductors depend strongly on the nature of the molecules, their conjugation and conformation, their mutual distance and the orientation between adjacent molecules. Variations of intramolecular distances and conformation disturb the conjugation and perturb the delocalization of charges. As a result, the mobility considerably decreases compared to that of a covalently well-organized crystal. Here, we present electrical characterization of large single crystals made of the regioregular octamer of 3-hexyl-thiophene (3HT)8 using a conductive-atomic force microscope (C-AFM) in air. We find a large anisotropy in the conduction with charge mobility values depending on the crystallographic orientation of the single crystal. The smaller conduction is in the direction of π-π stacking (along the long axis of the single crystal) with a mobility value in the order of 10(-3) cm(2) V(-1) s(-1), and the larger one is along the molecular axis (in the direction normal to the single crystal surface) with a mobility value in the order of 0.5 cm(2) V(-1) s(-1). The measured current-voltage (I-V) curves showed that along the molecular axis, the current followed an exponential dependence corresponding to an injection mode. In the π-π stacking direction, the current exhibits a space charge limited current (SCLC) behavior, which allows us to estimate the charge carrier mobility.
有机半导体的电子特性在很大程度上取决于分子的性质、它们的共轭和构象、它们之间的相互距离以及相邻分子之间的取向。分子内距离和构象的变化会干扰共轭并扰乱电荷的离域。结果，与共价有序排列的晶体相比，迁移率会大幅降低。在此，我们展示了在空气中使用导电原子力显微镜（C-AFM）对由3-己基噻吩（3HT）8的区域规整八聚体制成的大单晶进行的电学表征。我们发现传导中存在很大的各向异性，电荷迁移率值取决于单晶的晶体学取向。较小的传导方向是π-π堆积方向（沿单晶的长轴），迁移率值约为10^(-3) cm² V⁻¹ s⁻¹，而较大的传导方向是沿分子轴方向（垂直于单晶表面的方向），迁移率值约为0.5 cm² V⁻¹ s⁻¹。测量的电流-电压（I-V）曲线表明，沿分子轴方向，电流呈现出对应于注入模式的指数依赖性。在π-π堆积方向上，电流表现出空间电荷限制电流（SCLC）行为，这使我们能够估计电荷载流子迁移率。
