10 research outputs found

    Fabrication of Intrinsic, Elastic, Self-healing, and Luminescent CsPbBr<sub>3</sub> Quantum Dot-Polymer Composites via Thiol–Ene Cross-Linking

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    Here, we offer a straightforward approach for making elastic, self-healing, and light-conversion material, in which CsPbBr3 quantum dots (QDs) form a strong bond with a designed copolymer including elastic behavior based on the mechanical characteristics of polyisoprene and reversible bonding moieties for self-healing function. This designed composite film has highly luminescent and typically elastic properties, including good ultimate strength (∟0.14 N/mm2) and high stretchability (∟486%). The copolymer matrix exhibited excellent compatibility with CsPbBr3 QDs, in which they maintained their uniform distribution within the network after a serial stretching process due to the strong bond between copolymers and CsPbBr3 QDs. Furthermore, the composite film dynamic network is capable of 90% self-healing efficiency at room temperature without the need of any healing stimulus, heat, plasticizer, or solvent. This simple method suggested a relatively easy approach to a stable, elastic, and luminescent CsPbBr3 QD-based composite film that opens up the potential of fully stretchable light conversion material for light-emitting diodes

    Fabrication of Intrinsic, Elastic, Self-healing, and Luminescent CsPbBr<sub>3</sub> Quantum Dot-Polymer Composites via Thiol–Ene Cross-Linking

    No full text
    Here, we offer a straightforward approach for making elastic, self-healing, and light-conversion material, in which CsPbBr3 quantum dots (QDs) form a strong bond with a designed copolymer including elastic behavior based on the mechanical characteristics of polyisoprene and reversible bonding moieties for self-healing function. This designed composite film has highly luminescent and typically elastic properties, including good ultimate strength (∟0.14 N/mm2) and high stretchability (∟486%). The copolymer matrix exhibited excellent compatibility with CsPbBr3 QDs, in which they maintained their uniform distribution within the network after a serial stretching process due to the strong bond between copolymers and CsPbBr3 QDs. Furthermore, the composite film dynamic network is capable of 90% self-healing efficiency at room temperature without the need of any healing stimulus, heat, plasticizer, or solvent. This simple method suggested a relatively easy approach to a stable, elastic, and luminescent CsPbBr3 QD-based composite film that opens up the potential of fully stretchable light conversion material for light-emitting diodes

    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

    Fabrication of Intrinsic, Elastic, Self-healing, and Luminescent CsPbBr<sub>3</sub> Quantum Dot-Polymer Composites via Thiol–Ene Cross-Linking

    No full text
    Here, we offer a straightforward approach for making elastic, self-healing, and light-conversion material, in which CsPbBr3 quantum dots (QDs) form a strong bond with a designed copolymer including elastic behavior based on the mechanical characteristics of polyisoprene and reversible bonding moieties for self-healing function. This designed composite film has highly luminescent and typically elastic properties, including good ultimate strength (∟0.14 N/mm2) and high stretchability (∟486%). The copolymer matrix exhibited excellent compatibility with CsPbBr3 QDs, in which they maintained their uniform distribution within the network after a serial stretching process due to the strong bond between copolymers and CsPbBr3 QDs. Furthermore, the composite film dynamic network is capable of 90% self-healing efficiency at room temperature without the need of any healing stimulus, heat, plasticizer, or solvent. This simple method suggested a relatively easy approach to a stable, elastic, and luminescent CsPbBr3 QD-based composite film that opens up the potential of fully stretchable light conversion material for light-emitting diodes

    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

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

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    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 cm<sup>2</sup>/(V¡s)) and a high ON/OFF current ratio (>10<sup>6</sup>) 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-C<sub>61</sub>-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

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    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<sub><i>n</i></sub>, <i>n</i> = 1 or 2), referred to as MH-<i>b</i>-PStFl<sub><i>n</i></sub>. MH-<i>b</i>-PStFl<sub><i>n</i></sub> was prepared by the Cu­(I)-catalyzed click reaction of azido-terminated PStFl<sub><i>n</i></sub> (PStFl<sub><i>n</i></sub>-N<sub>3</sub>), which was obtained from the azidation reaction of the bromo-terminated PStFl<sub><i>n</i></sub> (PStFl<sub><i>n</i></sub>-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<sub><i>n</i></sub> 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<sub><i>n</i></sub>-based devices had the excellent hole mobility (0.25–0.52 cm<sup>2</sup> V<sup>–1</sup> s<sup>–1</sup>) and the high ON/OFF current (<i>I</i><sub>ON</sub>/<i>I</i><sub>OFF</sub>) ratio of 10<sup>7</sup>–10<sup>8</sup>, of which the MH-<i>b</i>-PStFl<sub>1</sub>-based one had the higher mobility than that of the MH-<i>b</i>-PStFl<sub>2</sub>-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>-PStFl<sub>2</sub>-based device showed a larger memory window than the MH-<i>b</i>-PStFl<sub>1</sub>-based one because the stronger electron-donating effect of the difluorenyl group in MH-<i>b</i>-PStFl<sub>2</sub> increased the charge storage capability of its related device. All the memory devices showed a long-term retention time over 10<sup>4</sup> s with the high <i>I</i><sub>ON</sub>/<i>I</i><sub>OFF</sub> ratio of 10<sup>6</sup>–10<sup>8</sup>. Among these devices, the MH-<i>b</i>-PStFl<sub>1</sub>-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

    Partially-Screened Field Effect and Selective Carrier Injection at Organic Semiconductor/Graphene Heterointerface

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    Due to the lack of a bandgap, applications of graphene require special device structures and engineering strategies to enable semiconducting characteristics at room temperature. To this end, graphene-based vertical field-effect transistors (VFETs) are emerging as one of the most promising candidates. Previous work attributed the current modulation primarily to gate-modulated graphene–semiconductor Schottky barrier. Here, we report the first experimental evidence that the partially screened field effect and selective carrier injection through graphene dominate the electronic transport at the organic semiconductor/graphene heterointerface. The new mechanistic insight allows us to rationally design graphene VFETs. Flexible organic/graphene VFETs with bending radius <1 mm and the output current per unit layout area equivalent to that of the best oxide planar FETs can be achieved. We suggest driving organic light emitting diodes with such VFETs as a promising application

    Ultrapure Green Light-Emitting Diodes Using Two-Dimensional Formamidinium Perovskites: Achieving Recommendation 2020 Color Coordinates

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    Pure green light-emitting diodes (LEDs) are essential for realizing an ultrawide color gamut in next-generation displays, as is defined by the recommendation (Rec.) 2020 standard. However, because the human eye is more sensitive to the green spectral region, it is not yet possible to achieve an ultrapure green electroluminescence (EL) with a sufficiently narrow bandwidth that covers >95% of the Rec. 2020 standard in the CIE 1931 color space. Here, we demonstrate efficient, ultrapure green EL based on the colloidal two-dimensional (2D) formamidinium lead bromide (FAPbBr<sub>3</sub>) hybrid perovskites. Through the dielectric quantum well (DQW) engineering, the quantum-confined 2D FAPbBr<sub>3</sub> perovskites exhibit a high exciton binding energy of 162 meV, resulting in a high photoluminescence quantum yield (PLQY) of ∼92% in the spin-coated films. Our optimized LED devices show a maximum current efficiency (η<sub>CE</sub>) of 13.02 cd A<sup>–1</sup> and the CIE 1931 color coordinates of (0.168, 0.773). The color gamut covers 97% and 99% of the Rec. 2020 standard in the CIE 1931 and the CIE 1976 color space, respectively, representing the “greenest” LEDs ever reported. Moreover, the device shows only a ∼10% roll-off in η<sub>CE</sub> (11.3 cd A<sup>–1</sup>) at 1000 cd m<sup>–2</sup>. We further demonstrate large-area (3 cm<sup>2</sup>) and ultraflexible (bending radius of 2 mm) LEDs based on 2D perovskites

    Stretchable Self-Healing Polymeric Dielectrics Cross-Linked Through Metal–Ligand Coordination

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    A self-healing dielectric elastomer is achieved by the incorporation of metal–ligand coordination as cross-linking sites in nonpolar polydimethylsiloxane (PDMS) polymers. The ligand is 2,2′-bipyridine-5,5′-dicarboxylic amide, while the metal salts investigated here are Fe<sup>2+</sup> and Zn<sup>2+</sup> with various counteranions. The kinetically labile coordination between Zn<sup>2+</sup> and bipyridine endows the polymer fast self-healing ability at ambient condition. When integrated into organic field-effect transistors (OFETs) as gate dielectrics, transistors with FeCl<sub>2</sub> and ZnCl<sub>2</sub> salts cross-linked PDMS exhibited increased dielectric constants compared to PDMS and demonstrated hysteresis-free transfer characteristics, owing to the low ion conductivity in PDMS and the strong columbic interaction between metal cations and the small Cl<sup>–</sup> anions which can prevent mobile anions drifting under gate bias. Fully stretchable transistors with FeCl<sub>2</sub>-PDMS dielectrics were fabricated and exhibited ideal transfer characteristics. The gate leakage current remained low even after 1000 cycles at 100% strain. The mechanical robustness and stable electrical performance proved its suitability for applications in stretchable electronics. On the other hand, transistors with gate dielectrics containing large-sized anions (BF<sub>4</sub><sup>–</sup>, ClO<sub>4</sub><sup>–</sup>, CF<sub>3</sub>SO<sub>3</sub><sup>–</sup>) displayed prominent hysteresis due to mobile anions drifting under gate bias voltage. This work provides insights on future design of self-healing stretchable dielectric materials based on metal–ligand cross-linked polymers
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