Department of Physics, Kent State University, Kent, OH, 44242, USA.
Organic Semiconductor Centre, SUPA, School of Physics and Astronomy, University of St Andrews, St Andrews, KY16 9SS, United Kingdom.
Sci Rep. 2018 Jan 15;8(1):699. doi: 10.1038/s41598-018-19157-9.
Liquid-crystalline organic semiconductors exhibit unique properties that make them highly interesting for organic optoelectronic applications. Their optical and electrical anisotropies and the possibility to control the alignment of the liquid-crystalline semiconductor allow not only to optimize charge carrier transport, but to tune the optical property of organic thin-film devices as well. In this study, the molecular orientation in a liquid-crystalline semiconductor film is tuned by a novel blading process as well as by different annealing protocols. The altered alignment is verified by cross-polarized optical microscopy and spectroscopic ellipsometry. It is shown that a change in alignment of the liquid-crystalline semiconductor improves charge transport in single charge carrier devices profoundly. Comparing the current-voltage characteristics of single charge carrier devices with simulations shows an excellent agreement and from this an in-depth understanding of single charge carrier transport in two-terminal devices is obtained. Finally, p-i-n type organic light-emitting diodes (OLEDs) compatible with vacuum processing techniques used in state-of-the-art OLEDs are demonstrated employing liquid-crystalline host matrix in the emission layer.
液晶有机半导体具有独特的性质，使其在有机光电应用中极具吸引力。它们的光学和电学各向异性以及控制液晶半导体取向的可能性不仅允许优化电荷载流子输运，而且还可以调整有机薄膜器件的光学性质。在这项研究中，通过一种新颖的刮刀法以及不同的退火方案来调整液晶半导体膜中的分子取向。通过正交偏光显微镜和光谱椭圆偏振术验证了这种取向的改变。结果表明，液晶半导体取向的改变可以极大地改善单电荷载流子器件中的电荷输运。通过将单电荷载流子器件的电流-电压特性与模拟进行比较，显示出极好的一致性，从而对两端器件中单电荷载流子输运有了深入的了解。最后，采用与最先进的 OLED 中使用的真空处理技术兼容的 p-i-n 型有机发光二极管（OLED），在发射层中使用液晶主体基质进行了演示。
