Tuning charge carrier transport and optical birefringence in liquid-crystalline thin films: a new design space for organic light-emitting diodes

Changmin Keum, Shiyi Liu, Akram Al-Shadeedi, Vikash Kaphle, Michiel Koen Callens, Lu Han, Kristiaan Neyts, Hongping Zhao, Malte Christian Gather, Scott D. Bunge, Robert J. Twieg, Antal Jakli, Björn Lüssem

Research output: Contribution to journalArticlepeer-review

12 Citations (Scopus)

Abstract

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.
Original languageEnglish
Article number699
Number of pages12
JournalScientific Reports
Volume8
DOIs
Publication statusPublished - 15 Jan 2018

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