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Conjugated Polymer- Based OFET Devices
Published in John R. Reynolds, Barry C. Thompson, Terje A. Skotheim, Conjugated Polymers, 2019
Mark Nikolka, Henning Sirringhaus
Easy processability, mechanical flexibility and the endless possibilities of molecular modifications to achieve, for example, performance improvements or analyte selectivity in sensing applications have staged organic field-effect transistors (OFETs) as one of the future trendsetting technologies. To date, OFET integration in applications ranging from rudimentary sensors and circuits to flexible low-resolution displays for electronic paper has been demonstrated. Concomitantly, more and more promising applications for OFETs such as fully flexible organic light-emitting diode (OLED) and organic TFT addressed liquid crystal displays (OLCDs), image sensing applications (e.g. X-Ray sensors), organic logic circuits and sensors for wearable applications come within reach.1–4 These novel applications require the use of high-performance, high-stability organic semiconductors with good uniformities imposing tight constraints on the choice of organic semiconductors. For a long time, small molecular semiconductors were deemed the best materials class to meet these rigorous requirements owing to high-mobility band transport observed in covalently bonded small molecule single crystals5,6; charge transport in such systems is widely thought to approach fundamental limits imposed by the weak van der Waals bonding and the polaronic nature of charge carriers in these molecular solids. Conjugated polymers, on the other hand, were considered too disordered to achieve similarly high charge carrier mobility and for a long time were considered inferior for industrial applications. Nevertheless, whereas small molecular organic semiconductors such as rubrene or pentacene potentially are able to deliver high performances in research laboratories, their high degree of crystallinity, polycrystalline nature and the inevitably resulting device-to-device variations in performance have caused concerns for large area applications, especially in the key displays market where device uniformity is as important as device performance. Due to their good film forming properties and more uniform thin film microstructures, conjugated polymers could offer potential advantages in order to meet these tight uniformity requirements. Therefore, conjugated polymers that can form percolating networks of chains allowing for both intrachain as well as interchain charge transport have attracted renewed interest in the community. These research efforts have led to a number of breakthroughs that have allowed conjugated polymers to approach performance values that were formerly thought impossible.
Nanoparticle-doped chiral nematic liquid-crystal composite and its effect in magnetic-response and electric-response flexible display
Published in Liquid Crystals, 2019
Wan-Li He, Meng-Die Yu, Ya-Jie Pang, Hao Ren, Jun-Liang Ma, Cheng Shi, Dong Wang, Hui Cao, Zhou Yang
Flexible liquid-crystal display (FLCD) is the next-generation technology of liquid-crystal display and has been widely used in various fields, including electronic paper, mobile phones and other electronics. FLCD exhibits some revolutionary features as compared with the traditional flat panel display or plasma display (see e.g. portability, durability and flexibility, low power consumption and easy fabrication in large areas). Although there are many other kinds of flexible display, such as the flexible organic light-emitting diode display [1], electrophoretic display [2] and the electro-wetting display [3,4], FLCD has the advantage of preparing large size screen with high resolution and larger colour gamut, and has drawn much attention for applications in E-paper[5–7]. For example, the cholesteric LC could be switched between the transmitted state (planar texture) and the light-scattering state (focal conic texture) under external electric fields with different frequency [8,9]. Meanwhile, chiral nematic LC can be used to prepare an electrically writable and thermally erasable device [10]. A defect-free bistable ferroelectric LC display with high-display contrast ratio was developed by using SiO deposition as smectic LC alignment, which was a very promising candidate for electronic flexible applications [11]. Moreover, due to the interaction between LC molecule and the polymer networks, polymer stabilising cholesteric LC also had the advantage of preparing electronic paper, which could exhibit white and black display by using grey-scale potential with flexible feature [12,13]. However, the flexible LC application still suffered from complicated driving electronic electrodes, which often was difficult for flexible display due to the low durability of the conductor as well as the connect bonding. In addition, the low mechanical stability, low contrast ratio of display and the high energy consumption of FLCD were urgently needed to be solved.