8 research outputs found

    Synthesis and Properties of Oxygen-Linked <i>N</i>-Phenylcarbazole Dendrimers

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    A series of novel oxygen-linked <i>N</i>-phenylcarbazole (NPC) dendritic wedges (<b>3</b>–<b>5</b>) and triphenylamine-centered dendrimers (<b>CBD-G0</b> to <b>-G2</b>) have been synthesized and extensively studied. The aryl–oxygen–aryl (Ar–O–Ar) linkages were established on 3,6-positions of carbazole and 4-position of <i>N</i>-phenyl group. UV–vis spectra revealed that the Ar–O–Ar linkage would break down the π conjugation and make NPC units manifest their individual absorption moiety. Both steady-state luminescence and fluorescence decay dynamics at room temperature and 77 K in tetrahydrofuran suggested that the transfer of energy from the carbazole wedges to the triphenylamine (TPA) core operates in <b>CBD-G1</b>, so that the luminescence mainly arises from the core unit. The quenching of the emission from carbazole wedges by the TPA core becomes less effective as the generation develops into <b>CBD-G2</b>. The oxidation potential of the NPC derivatives clearly revealed the mesomeric electron-donating effect of the oxygen atom and inductive electron-withdrawing effect of the carbazole unit. The potential gradient could be established on those triphenylamine-centered dendrimers (<b>CBD-G1</b> and <b>CBD-G2</b>), such that the outer layer is electron-poor and the inner layer is electron-rich. It is remarkable that the HOMO level of the NPC dendrimers is as high as −5.17 eV and triplet energy level is kept above 2.85 eV. These levels of HOMO and triplet energy, together with good thermal stability and compatibility of solution processing, make NPC dendrimers ideal host materials for blue triplet emitters. Using <b>CBD-G2</b> as the host material, the FIrpic-doped solution-processed light-emitting diodes were fabricated, and maximum luminous efficiency could be achieved at a record high of 24.7 cd/A at 484 cd/m<sup>2</sup>

    1,3,4-Oxadiazole Containing Silanes as Novel Hosts for Blue Phosphorescent Organic Light Emitting Diodes

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    Five rigid oxadiazole (OXD) containing silanes, denoted <b>1</b>–<b>5</b>, have been developed with high morphological stability. Disruption of the π-aromatic conjugation by introduction of Si atoms leads to a large band gap and high triplet energy. Among the OXDs we studied, 2,5-bis(triphenylsilylphenyl)-1,3,4-oxadiazole <b>5</b> is the best host for FIrpic, with a phosphorescent organic light emitting diode (PHOLED) turn-on voltage of 6.9 V, maximum luminance of 5124 cd/m<sup>2</sup>, current efficiency of 39.9 cd/A, and external quantum efficiency of 13.1%. Special molecular stacking in the single crystal of <b>5</b> was discussed

    Novel Ambipolar Orthogonal Donor–Acceptor Host for Blue Organic Light Emitting Diodes

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    Ambipolar triplet hosts comprising 1,2,4-triazole and carbazole in ortho-positions have been developed. The blue PHOLED has a high current efficiency of 47.1 cd A<sup>–1</sup>, power efficiency of 41.2 lm W<sup>–1</sup>, and low efficiency roll-off. The high efficiency was attributed to the successful control of π-conjugation through orthogonal arrangement of the substituents so that a wide T<sub>1</sub>–S<sub>0</sub> gap could be maintained

    Novel Ambipolar Orthogonal Donor–Acceptor Host for Blue Organic Light Emitting Diodes

    No full text
    Ambipolar triplet hosts comprising 1,2,4-triazole and carbazole in ortho-positions have been developed. The blue PHOLED has a high current efficiency of 47.1 cd A<sup>–1</sup>, power efficiency of 41.2 lm W<sup>–1</sup>, and low efficiency roll-off. The high efficiency was attributed to the successful control of π-conjugation through orthogonal arrangement of the substituents so that a wide T<sub>1</sub>–S<sub>0</sub> gap could be maintained

    Novel Ambipolar Orthogonal Donor–Acceptor Host for Blue Organic Light Emitting Diodes

    No full text
    Ambipolar triplet hosts comprising 1,2,4-triazole and carbazole in ortho-positions have been developed. The blue PHOLED has a high current efficiency of 47.1 cd A<sup>–1</sup>, power efficiency of 41.2 lm W<sup>–1</sup>, and low efficiency roll-off. The high efficiency was attributed to the successful control of π-conjugation through orthogonal arrangement of the substituents so that a wide T<sub>1</sub>–S<sub>0</sub> gap could be maintained

    Orthogonally Substituted Benzimidazole-Carbazole Benzene As Universal Hosts for Phosphorescent Organic Light-Emitting Diodes

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    The novel ambipolar hosts of <i><b>o</b></i><b>-CbzBz</b> and <i><b>o</b></i><b>-DiCbzBz</b> contain carbazole and benzimidazole through an <i>ortho</i>-connection. The orthogonal conformations cause the triplet state to be confined at the carbazole units to secure efficient energy transfer. The phosphorescent organic light-emitting diodes (PhOLEDs) show a high current efficiency, power efficiency, and low efficiency roll-off. <i><b>o</b></i><b>-DiCbzBz</b> can be used as a host for sky-blue, green, and orange-red PhOLEDs, giving 57.5, 78.4, and 60.3 cd/A, respectively

    High <i>K</i> Nanophase Zinc Oxide on Biomimetic Silicon Nanotip Array as Supercapacitors

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    A 3D trenched-structure metal–insulator–metal (MIM) nanocapacitor array with an ultrahigh equivalent planar capacitance (EPC) of ∼300 μF cm<sup>–2</sup> is demonstrated. Zinc oxide (ZnO) and aluminum oxide (Al<sub>2</sub>O<sub>3</sub>) bilayer dielectric is deposited on 1 μm high biomimetic silicon nanotip (SiNT) substrate using the atomic layer deposition method. The large EPC is achieved by utilizing the large surface area of the densely packed SiNT (∼5 × 10<sup>10</sup> cm<sup>–2</sup>) coated conformally with an ultrahigh dielectric constant of ZnO. The EPC value is 30 times higher than those previously reported in metal–insulator–metal or metal–insulator–semiconductor nanocapacitors using similar porosity dimensions of the support materials

    The Effects of Fluorine-Contained Molecules on Improving the Polymer Solar Cell by Curing the Anomalous S‑Shaped <i>I</i>–<i>V</i> Curve

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    In this study, we investigate the effects of fluorinated poly­(3,4-ethylene dioxythiophene):poly­(styrenesulfonate) buffer layer on the performance of polymer photovoltaic cells. We demonstrate for the first time, the deterioration of the device performance can be effectively mended by modifying the interface between the active layer and buffer layer with heptadecafluoro-1,1,2,2-tetra-hydro-decyl trimethoxysilane (PFDS) and perfluorononane. Device performance shows a substantial enhancement of short-circuit current from 7.90 to 9.39 mA/cm<sup>2</sup> and fill factor from 27% to 53%. The overall device efficiency was improved from 0.98% to 3.12% for PFDS modified device. The mechanism of S-shape curing is also discussed. In addition, the stability of modified devices shows significant improvement than those without modification. The efficiency of the modified devices retains about half (1.88%) of its initial efficiency (4.1%) after 30 d compared to the unmodified ones (0.61%), under air atmosphere
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