Department of Physics, Wake Forest University, Winston-Salem, NC 27109.
Division of Physical Science and Engineering, King Abdullah University of Science and Technology, Thuwal 23955-6900, Saudi Arabia.
Proc Natl Acad Sci U S A. 2017 Aug 15;114(33):E6739-E6748. doi: 10.1073/pnas.1705164114. Epub 2017 Jul 24.
The temperature dependence of the charge-carrier mobility provides essential insight into the charge transport mechanisms in organic semiconductors. Such knowledge imparts critical understanding of the electrical properties of these materials, leading to better design of high-performance materials for consumer applications. Here, we present experimental results that suggest that the inhomogeneous strain induced in organic semiconductor layers by the mismatch between the coefficients of thermal expansion (CTE) of the consecutive device layers of field-effect transistors generates trapping states that localize charge carriers. We observe a universal scaling between the activation energy of the transistors and the interfacial thermal expansion mismatch, in which band-like transport is observed for similar CTEs, and activated transport otherwise. Our results provide evidence that a high-quality semiconductor layer is necessary, but not sufficient, to obtain efficient charge-carrier transport in devices, and underline the importance of holistic device design to achieve the intrinsic performance limits of a given organic semiconductor. We go on to show that insertion of an ultrathin CTE buffer layer mitigates this problem and can help achieve band-like transport on a wide range of substrate platforms.
电荷载流子迁移率的温度依赖性为有机半导体中的电荷输运机制提供了重要的见解。这种知识赋予了对这些材料的电性能的关键理解，从而为消费类应用的高性能材料的设计提供了更好的指导。在这里，我们提出的实验结果表明，由场效应晶体管的连续器件层之间的热膨胀系数（CTE）不匹配引起的有机半导体层中的不均匀应变会产生陷获态，使电荷载流子局域化。我们观察到晶体管的激活能与界面热膨胀失配之间存在普遍的标度关系，其中类似 CTE 下观察到能带传输，否则则为激活传输。我们的结果表明，高质量的半导体层对于在器件中获得有效的电荷载流子传输是必要的，但不是充分的，并且强调了整体器件设计对于实现给定有机半导体的固有性能限制的重要性。我们接着表明，插入超薄 CTE 缓冲层可以减轻这个问题，并有助于在广泛的衬底平台上实现能带传输。
