Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN, 55455, USA.
Institut Néel CNRS and Grenoble Alpes University, 25 rue des Martyrs, Grenoble, 38042, France.
Nat Commun. 2018 May 30;9(1):2141. doi: 10.1038/s41467-018-04479-z.
Understanding relationships between microstructure and electrical transport is an important goal for the materials science of organic semiconductors. Combining high-resolution surface potential mapping by scanning Kelvin probe microscopy (SKPM) with systematic field effect transport measurements, we show that step edges can trap electrons on the surfaces of single crystal organic semiconductors. n-type organic semiconductor crystals exhibiting positive step edge surface potentials display threshold voltages that increase and carrier mobilities that decrease with increasing step density, characteristic of trapping, whereas crystals that do not have positive step edge surface potentials do not have strongly step density dependent transport. A device model and microelectrostatics calculations suggest that trapping can be intrinsic to step edges for crystals of molecules with polar substituents. The results provide a unique example of a specific microstructure-charge trapping relationship and highlight the utility of surface potential imaging in combination with transport measurements as a productive strategy for uncovering microscopic structure-property relationships in organic semiconductors.
理解微观结构和电输运之间的关系是有机半导体材料科学的一个重要目标。通过扫描 Kelvin 探针显微镜 (SKPM) 进行高分辨率表面电势映射，并结合系统的场效应输运测量，我们表明台阶边缘可以在单晶有机半导体的表面捕获电子。表现出正台阶边缘表面电势的 n 型有机半导体晶体的阈值电压随台阶密度的增加而增加，载流子迁移率随台阶密度的增加而降低，这是捕获的特征，而没有正台阶边缘表面电势的晶体则没有强烈依赖于台阶密度的输运。器件模型和微电子静电计算表明，对于具有极性取代基的分子晶体，台阶边缘的捕获可能是固有存在的。这些结果提供了一个特定微观结构-电荷捕获关系的独特示例，并强调了表面电势成像与输运测量相结合作为揭示有机半导体微观结构-性能关系的有效策略的实用性。
