Using a Single Electrospun Polymer Nanofiber to Enhance Carrier Mobility in Organic Field-Effect Transistors toward Nonvolatile Memory

In this work, a single electrospun polymer nanofiber was employed as an additional dielectric in organic field-effect transistors where the active channel was a layer of pentacene. A high field-effect mobility (>1.50 cm²/(V·s)) and a high ON/OFF current ratio (>10⁶) could be achieved by the use of such a nanofiber. Probing by electron microscopy, atomic force microscopy, and scattering techniques, we found that the geometry of the fiber is key to induce a pentacene morphology with large and oriented grains that facilitates the charge transport in pentacene layer along the fiber. The feasibility of nonvolatile memory based on this new type of transistor has been explored and the devices showed a fairly high memory window and reliable memory characteristics. In addition to pure polymers, the effects of composite nanofibers with dispersed [6,6]-phenyl-C₆₁-butyric acid methyl ester were also investigated, and the electrical properties and memory characteristics of the transistors were found to be further improved. This study highlights the importance of dielectric geometry to pentacene morphology that is decisive for the performances of organic field-effect transistors

Synthesis of Oligosaccharide-Based Block Copolymers with Pendent π‑Conjugated Oligofluorene Moieties and Their Electrical Device Applications

We report the synthesis and electric device applications of oligosaccharide-based diblock copolymers consisting of a maltoheptaose (MH) block and a poly­(4-oligofluorenyl­styrene) block (PStFl_<i>n</i>, <i>n</i> = 1 or 2), referred to as MH-<i>b</i>-PStFl_<i>n</i>. MH-<i>b</i>-PStFl_<i>n</i> was prepared by the Cu­(I)-catalyzed click reaction of azido-terminated PStFl_<i>n</i> (PStFl_<i>n</i>-N₃), which was obtained from the azidation reaction of the bromo-terminated PStFl_<i>n</i> (PStFl_<i>n</i>-Br), with excess ethynyl-terminated MH in the THF/DMF mixture solvent. The resulting diblock copolymers self-assembled to spherical microdomains with sub-10 nm sizes in both bulk and thin film state after annealing process. Thereafter, the MH-<i>b</i>-PStFl_<i>n</i> thin film (∼50 nm) with the self-assembled nanoscale spherical aggregates was used as the charge storage layer for the pentacene-based field-effect transistor type memory devices. The MH-<i>b</i>-PStFl_<i>n</i>-based devices had the excellent hole mobility (0.25–0.52 cm² V^–1 s^–1) and the high ON/OFF current (<i>I</i>_ON/<i>I</i>_OFF) ratio of 10⁷–10⁸, of which the MH-<i>b</i>-PStFl₁-based one had the higher mobility than that of the MH-<i>b</i>-PStFl₂-based one because the pentacene crystal in the former device possessed the larger grain size and fewer boundaries. On the other hand, the MH-<i>b</i>-PStFl₂-based device showed a larger memory window than the MH-<i>b</i>-PStFl₁-based one because the stronger electron-donating effect of the difluorenyl group in MH-<i>b</i>-PStFl₂ increased the charge storage capability of its related device. All the memory devices showed a long-term retention time over 10⁴ s with the high <i>I</i>_ON/<i>I</i>_OFF ratio of 10⁶–10⁸. Among these devices, the MH-<i>b</i>-PStFl₁-based device showed a good WRER endurance over 180 cycles. This work not only demonstrates the tunable electrical memory characteristics by adjusting the π-conjugation length of the oligofluorenyl side chain in the polymer electret but also provides a promising approach for developing the next-generation “green electronics” using natural materials

Isoindigo-Based Semiconducting Polymers Using Carbosilane Side Chains for High Performance Stretchable Field-Effect Transistors

Isoindigo-based conjugated polymers, PII2T-C6 and PII2T-C8, with carbosilane side chains have been designed and synthesized for stretchable electronic applications. The carbosilane side chains offerred a simple synthetic pathway to evaluate long and branched side chains in high yields and were prepared with a six or eight linear spacer plus two hexyl or octyl chains after branching. The studied polymers showed a high charge carrier mobility of 8.06 cm² V^–1 s^–1 with an on/off current ratio of 10⁶ as probed using a top-contact transistor device with organized solid state molecular packing structures, as investigated through grazing-incidance X-ray diffreaction (GIXD) and atomic force microscopy (AFM) technique systematically. The studied polymers, more attractive, exhibited superior thin film ductility with a low tensile modulus in a range of 0.27–0.43 GPa owing to the branched carbosilane side chain, and their mobility was remained higher than 1 cm² V^–1 s^–1 even under a 60% strain along parallel or perpendicular direction to the tensile strain. Such polymer films, in addition, can be simultaneously operated over 400 stretching/releasing cycles and maintained stable electrical properties, suggesting the newly designed materials possessed great potential for next-generation skin-inspired wearable electronic application with high charge carrier mobility, low tensile modulus, and stable device characteristics during stretching