27 research outputs found

    Nonvolatile Organic Thin Film Transistor Memory Devices Based on Hybrid Nanocomposites of Semiconducting Polymers: Gold Nanoparticles

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    We report the facile fabrication and characteristics of organic thin film transistor (OTFT)-based nonvolatile memory devices using the hybrid nanocomposites of semiconducting poly­(9,9-dioctylfluorene-alt-bithiophene) (F8T2) and ligand-capped Au nanoparticles (NPs), thereby serving as a charge storage medium. Electrical bias sweep/excitation effectively modulates the current response of hybrid memory devices through the charge transfer between F8T2 channel and functionalized Au NPs trapping sites. The electrical performance of the hybrid memory devices can be effectively controlled though the loading concentrations (0–9 %) of Au NPs and organic thiolate ligands on Au NP surfaces with different carbon chain lengths (Au-L6, Au-L10, and Au-L18). The memory window induced by voltage sweep is considerably increased by the high content of Au NPs or short carbon chain on the ligand. The hybrid nanocomposite of F8T2:9% Au-L6 provides the OTFT memories with a memory window of ∼41 V operated at ±30 V and memory ratio of ∼1 × 10<sup>3</sup> maintained for 1 × 10<sup>4</sup> s. The experimental results suggest that the hybrid materials of the functionalized Au NPs in F8T2 matrix have the potential applications for low voltage-driven high performance nonvolatile memory devices

    Stretchable Polymer Dielectrics for Low-Voltage-Driven Field-Effect Transistors

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    A stretchable and mechanical robust field-effect transistor is essential for soft wearable electronics. To realize stretchable transistors, elastic dielectrics with small current hysteresis, high elasticity, and high dielectric constants are the critical factor for low-voltage-driven devices. Here, we demonstrate the polar elastomer consisting of poly­(vinyli­dene fluoride-hexa­fluoro­propylene) (PVDF-HFP):​poly­(4-vinyl­phenol) (PVP). Owing to the high dielectric constant of PVDF-HFP, the device can be operated under less than 5 V and shows a linear-regime hole mobility as high as 0.199 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> without significant current hysteresis. Specifically, the PVDF-HFP:​PVP blends induce the vertical phase separation and significantly reduce current leakage and reduce the crystallization of PVDF segments, which can contribute current hysteresis in the OFET characteristics. All-stretchable OFETs based on these PVDF-HFP:​PVP dielectrics were fabricated. The device can still keep the hole mobility of approximately 0.1 cm<sup>2</sup>/​(V s) under a low operation voltage of 3 V even as stretched with 80% strain. Finally, we successfully fabricate a low-voltage-driven stretchable transistor. The low voltage operating under strains is the desirable characteristics for soft and comfortable wearable electronics

    Biaxially Extended Conjugated Polymers with Thieno[3,2‑<i>b</i>]thiophene Building Block for High Performance Field-Effect Transistor Applications

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    Biaxially thiophene side chain extended thieno­[3,2-<i>b</i>]­thiophene (TT2T)-based polymers, PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T, were synthesized by Stille coupling polymerization with different conjugated moieties of thiophene (T), bithiophene (2T), thieno­[3,2-<i>b</i>]­thiophene (TT), and thiophene–vinylene–thiophene (TVT), respectively. The electronic properties of the prepared polymers could be effectively tuned because the variant π-conjugated building block affected the backbone conformation and the resulted morphology. The morphology of the thin films characterized by atomic force microscopy and grazing incidence X-ray diffraction showed that P2TTT2T and PTVTTT2T thin films possessed a better molecular packing with a nanofiber structure owing to their coplanar backbone. The average field-effect mobilities of PTTT2T, P2TTT2T, PTTTT2T, and PTVTTT2T were 6.7 × 10<sup>–6</sup>, 0.36, 2.2 × 10<sup>–3</sup>, and 0.64 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> (maximum 0.71), respectively, attributed to the coplanarity of polymer skeleton. In addition, the fabricated FET devices showed a high on/off ratio over 10<sup>7</sup> under ambient for over 3 months, suggesting the excellent environmental stability. The above results demonstrated that the biaxially extended fused thiophene based conjugated polymers could serve as a potential candidate for organic electronic device applications

    Interplay between the Phase Transitions at Different Length Scales in the Supramolecular Comb–Coil Block Copolymers Bearing (AB)<sub><i>n</i></sub> Multiblock Architecture

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    We introduced the concept of comb–coil supramolecule into linear (AB)<sub><i>n</i></sub>-type multiblock copolymer and investigated the self-assembly behavior of the copolymers as a function of the unit number <i>n</i>. Linear (polystyrene-<i>block</i>-poly­(2-vinylpyridine))<sub><i>n</i></sub> (denoted as (PS-<i>b</i>-P2VP)<sub><i>n</i></sub>, where <i>n</i> = 1, 2, 3) was complexed with a surfactant, dodecylbenzenesulfonic acid (DBSA), to yield the comb–coil multiblock copolymers, in which DBSA bound stoichiometrically with P2VP block via physical bonds. All three comb–coil block copolymers, including diblock (<i>n</i> = 1), tetrablock (<i>n</i> = 2), and hexablock (<i>n</i> = 3), self-organized to form cylinder-<i>within</i>-lamellae morphology at the lower temperature, where the cylindrical microdomains formed by the PS block embedded in the matrix composed of the lamellar mesophase organized by the P2VP­(DBSA) comb block. The disordering of the smaller-scale lamellar mesophase formed by the comb block occurred upon heating; at the same time, the larger-scale cylindrical domains transformed to body-centered cubic-packed spheres in the diblock complex and to another hexagonally packed cylinder structure with smaller domain spacing in tetrablock and hexablock complexes, indicating that the order–disorder transition (ODT) of the smaller-scale structure drove an order–order transition (OOT) of the larger-scale structure irrespective of <i>n</i>. The transition temperatures were found to increase with increasing <i>n</i> due to the introduction of more interfacial area in the microphase-separated state of the multiblock with larger unit number

    Signal intensity of tumor tissue on MCE-MRI.

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    <p>(A) Signal intensity and (B) relative signal enhancement in the endometrial and cervical cancer prior to (time = 0 s) and after contrast administration. * = p < 0.05, ** = p < 0.01 by unpaired t-test. Data are expressed as mean ± SEM. Abbreviations: SI, signal intensity; SI<sub>0</sub>, pre-contrast SI<sub>t</sub>; SI following contrast administration; SI<sub>relative</sub>, relative signal enhancement.</p

    High-Performance Nonvolatile Organic Transistor Memory Devices Using the Electrets of Semiconducting Blends

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    Organic nonvolatile transistor memory devices of the <i>n</i>-type semiconductor <i>N</i>,<i>N</i>′-bis­(2-phenylethyl)-perylene-3,4:9,10-tetracarboxylic diimide (BPE-PTCDI) were prepared using various electrets (i.e., three-armed star-shaped poly­[4-(diphenylamino)­benzyl methacrylate] (N­(PTPMA)<sub>3</sub>) and its blends with 6,6-phenyl-C<sub>61</sub>-butyric acid methyl ester (PCBM), 6,13-bis­(triisopropylsilylethynyl)­pentacene (TIPS-pen) or ferrocene). In the device using the PCBM:N­(PTPMA)<sub>3</sub> blend electret, it changed its memory feature from a write-once-read-many (WORM) type to a flash type as the PCBM content increased and could be operated repeatedly based on a tunneling process. The large shifts on the reversible transfer curves and the hysteresis after implementing a gate bias indicated the considerable charge storage in the electret layer. On the other hand, the memory characteristics showed a flash type and a WORM characteristic, respectively, using the donor/donor electrets TIPS-pen:N­(PTPMA)<sub>3</sub> and ferrocene:N­(PTPMA)<sub>3</sub>. The variation on the memory characteristics was attributed to the difference of energy barrier at the interface when different types of electret materials were employed. All the studied memory devices exhibited a long retention over 10<sup>4</sup> s with a highly stable read-out current. In addition, the afore-discussed memory devices by inserting another electret layer of poly­(methacrylic acid) (PMAA) between the BPE-PTCDI layer and the semiconducting blend layer enhanced the write-read-erase-read (WRER) operation cycle as high as 200 times. This study suggested that the energy level and charge transfer in the blend electret had a significant effect on tuning the characteristics of nonvolatile transistor memory devices

    Synthesis, Morphology, and Field-Effect Transistor Characteristics of Crystalline Diblock Copolymers Consisted of Poly(3-hexylthiophene) and Syndiotactic Polypropylene

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    We report the synthesis, morphology, and the field effect transistor (FET) characteristics of the crystalline diblock copolymers of poly­(3-hexylthiophene) and syndiotactic polypropylene (P3HT-<i>b</i>-sPP). Four diblock copolymers with various sPP block lengths, P3HT<sub>16K</sub>-<i>b-</i>sPP<sub>3K</sub> (P1), P3HT<sub>16K</sub>-<i>b-</i>sPP<sub>6K </sub>(P2), P3HT<sub>16K</sub>-<i>b-</i>sPP<sub>9K </sub>(P3), and P3HT<sub>16K</sub>-<i>b-</i>sPP<sub>14K</sub> (P4), were prepared by the click coupling of N<sub>3</sub>-capped sPP and ethynyl-capped P3HT. The stereoregular crystalline block sPP developed different types of molecular stacking structures and led the P3HT domains to pack lamellar edge-on structure with improved charge transporting characteristics, as evidenced by the grazing incidence wide-angle X-ray scattering (GIWAXS), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The FET hole mobilities of P1–P3 thin films were 4.15 × 10<sup>–3</sup>, 4.16 × 10<sup>–2</sup>, and 3.95 × 10<sup>–3</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, respectively, which were up to 1 order of magnitude higher than that of the parent P3HT thin film (1.43 × 10<sup>–3</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>). The crystalline-stereoregular crystalline diblock P3HT-<i>b</i>-sPP demonstrates that using the lattice matching concept could well clarify the molecular stacking structure of conjugated polymer segments in order to further improve the performance of organic electron devices

    Synthesis, Morphology, and Sensory Applications of Multifunctional Rod–Coil–Coil Triblock Copolymers and Their Electrospun Nanofibers

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    We report the synthesis, morphology, and applications of conjugated rod–coil–coil triblock copolymers, polyfluorene<i>-block-</i>poly­(<i>N</i>-isopropylacrylamide)<i>-block</i>-poly­(N-methylolacrylamide) (<b>PF</b><b>-</b><i><b>b</b></i><b>-</b><b>PNIPAAm</b><i><b>-b-</b></i><b>PNMA</b>), prepared by atom transfer radical polymerization first and followed by click coupling reaction. The blocks of PF, PNIPAAm, and PNMA were designed for fluorescent probing, hydrophilic thermo-responsive and chemically cross-linking, respectively. In the following, the electrospun (ES) nanofibers of PF-<i>b</i>-PNIPAAm-<i>b</i>-PNMA were prepared in pure water using a single-capillary spinneret. The SAXS and TEM results suggested the lamellar structure of the <b>PF</b><b>-</b><i><b>b</b></i><b>-</b><b>PNIPAAm</b><b>-</b><i><b>b</b></i><b>-</b><b>PNMA</b> along the fiber axis. These obtained nanofibers showed outstanding wettability and dimension stability in the aqueous solution, and resulted in a reversible on/off transition on photoluminescence as the temperatures varied. Furthermore, the high surface/volume ratio of the ES nanofibers efficiently enhanced the temperature-sensitivity and responsive speed compared to those of the drop-cast film. The results indicated that the ES nanofibers of the conjugated rod–coil block copolymers would have potential applications for multifunctional sensory devices

    Synthesis and Characterization of All-Conjugated Graft Copolymers Comprised of n‑Type or p‑Type Backbones and Poly(3-hexylthiophene) Side Chains

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    All-conjugated graft copolymers containing poly­(3-hexylthiophene) (P3HT) side chains and both of p-type and n-type backbones that are connected with all π-conjugated linkages were synthesized via a two-step method involving the Stille coupling reaction and Kumada catalyst-transfer polycondensation (KCTP). A series of naphthalene diimide copolymers with different compositions of 3-(4′-chloro-3′-tolyl)­thiophene (CTT) units (PNDICTT) were designed as n-type backbones, while the poly­(3-(4′-chloro-3′-tolyl)­thiophene-<i>alt</i>-thiophene) (PCTT) was designed as a p-type backbone which were converted into n-type or p-type macroinitiators, and P3HT side chains were then <i>in situ</i> grafted from the macroinitiators via an externally initiated KCTP at room temperature. By using this newly developed two-step method for the synthesis of all-conjugated graft copolymers, the number of P3HT side chains in the graft copolymers can be simply controlled by varying the composition of the CTT units in PNDICTT. Meanwhile, the chain length of P3HT was controllable by varying the feed molar ratio of the thiophene monomer to CTT unit during the KCTP. The optical and electrochemical properties of the all-conjugated graft copolymers were investigated by UV–vis, cyclic voltammetry (CV), and organic field-effect transistor (OFET) measurements. Moreover, the differential scanning calorimetry (DSC) and grazing incident wide-angle X-ray scattering (GIWAXS) results revealed that there were two distinguished crystalline domains in the thin films of the graft copolymer. The morphology of the graft copolymers was first observed by transmission electron microscopy (TEM), in which there was a microphase separation between the PNDICTT and P3HT domains, and the P3HT domains showed partial nanofibril structures with a width of 10–20 nm

    Interplay of Molecular Orientation, Film Formation, and Optoelectronic Properties on Isoindigo- and Thienoisoindigo-Based Copolymers for Organic Field Effect Transistor and Organic Photovoltaic Applications

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    A systematic study on the effects of heteroarenes on the solid state structure and optoelectronic properties of isoindigo analogues, namely, PBDT-IIG and PBDT-TIIG, used in solution-processed organic field effect transistors (OFETs) and organic photovoltaics (OPVs) is reported. We discover that the optical absorption, frontier orbitals, backbone coplanarity, molecular orientation, solubility, film morphology, charge carrier mobility, and solar cell performance are critically influenced by the heteroarenes in the acceptor subunits. PBDT-IIG exhibits good p-type OFET performance with mobility up to 1.03 × 10<sup>–1</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>, whereas PBDT-TIIG displays ambipolar mobilities of μ<sub>h</sub> = 7.06 × 10<sup>–2</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup> and μ<sub>e</sub> = 2.81 × 10<sup>–4</sup> cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>. PBDT-IIG and PBDT-TIIG blended with [6,6]-phenyl-C<sub>71</sub>-butyric acid methyl ester (PC<sub>71</sub>BM) yield promising power conversion efficiencies (PCEs) of 5.86% and 2.55%, respectively. The excellent mobility of PBDT-IIG can be attributable to the growing fraction of edge-on packing by the interfacial surface treatment. Although PBDT-TIIG could construct a long-range face-on packing alignment to meliorate its photocurrent in OPV applications, the low open-circuit voltage caused by its high-lying HOMO energy level and greater recombination demonstrates the trade-off between light absorption and solar cell performance. Nevertheless, PBDT-TIIG with a PCE of 2.55% is the highest reported PCE to date for the TIIG-based systems
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