Efficiency enhancement of solution‐processed single‐layer blue‐phosphorescence organic light‐emitting devices having co‐host materials of polymer (PVK) and small‐molecule (SimCP2)

Abstract— A new type of single‐layer blue‐phosphorescence organic light‐emitting devices (OLEDs) containing poly(9‐vinylcarbazole) (PVK) and small‐molecule‐based amorphous ambipolar bis(3,5‐di(^9H‐carbazol‐9‐yl)phenyl) diphenylsilane (SimCP2) as the co‐host material have been demonstrated. All active materials [PVK, SimCP2, Flrpic (blue‐phosphorescence dopant), and OXD‐7 (electron transport)] were mixed in a single layer for solution processing in the fabrication of OLEDs. The SimCP2 small‐molecule host has adequate high electron and hole‐carrier mobiltieis of ～10^?4 cm²/V‐sec and a sufficiently large triplet state energy of ～2.70 eV in confining emission energy on FIrpic. Based on such an architecture for single‐layer devices, a maximum external quantum efficiency of 6.2%, luminous efficiency of 15.8 cd/A, luminous power efficiency of 11 lm/W, and Commision Internale de l'Eclairage (CIE^x,y) coordinates of (0.14,0.32) were achieved. Compared with those having PVK as the single‐host material, the improvement in the device performance is attributed to the balance of hole and electron mobilities of the co‐host material, efficient triplet‐state energy confinement on FIrpic, and the high homogeneity of the thin‐film active layer. Flexible blue‐phosphorescence OLEDs based on solution‐processed SimCP2 host material (withou PVK) have been demonstrated as well.     

Photophysical studies of polyvinylcarbazole polymer films

Polyvinylcarbazole (PVK) films have been prepared by solution method. Their absorption spectra, photoluminescence, and electroluminescence have been studied. Absorption in pure PVK is found to be high at lower wavelengths in UV region and decreases in visible range. In case of I₂ doped PVK, absorption is observed in visible region also. The photoluminescence is obtained in pure PVK when exited by violet or blue light but in case of I₂ doped PVK, similar excitation gives low intensity peaks in yellow–green region. The results indicate that I₂ levels in PVK causes absorption in 400–600 nm wavelength range and makes the deexcitation of the molecules nonradiative. Light emission by application of ac voltage from mains up to 100 V has been studied. Nonlinear increase in emission intensity has been observed with increasing voltage. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 722–726, 2007     

Effects of polymer concentration and zone drawing on the physical properties of poly(N‐vinylcarbazole) thick film

To check the possibility of zone‐drawn poly(N‐vinylcarbazole) (PVK) thick films as base materials of photorefractive polymers, the effects of the initial polymer concentration and zone drawing on the physical properties of PVK film were investigated. PVK films were prepared from 1,1,2,2‐tetrachloroethane (TCE) solutions with different initial concentrations. To investigate the drawing behavior of the PVK films with different solution concentrations, the films were drawn under various zone‐drawing conditions. Through a series of experiments, it turned out that the initial concentration of the PVK solution in TCE caused significant changes in the draw ratio of the PVK film, that is, the zone draw ratios of the film at an initial concentration of 9.8 g/dL exhibited their maximum values and gradually decreased at higher or lower concentrations. Thus, it was determined that the initial concentration of 9.8 g/dL is the optimum polymer concentration to produce the maximum draw ratio in this work. The lightness (whiteness) of the zone‐drawn PVK film was much higher than that of the hot‐drawn PVK film, resulting from diminishing microcrystallite formation, crystallization, and back‐folding of molecular chains by zone drawing. Moreover, the mechanical properties of the PVK film were dominantly improved by introducing a zone‐drawing technique, maintaining lightness of the zone‐drawn film to a similar degree as that of the undrawn film. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1297–1304, 2001     

多孔硅与有机发光材料复合的光电特性

用旋涂法实现了多孔硅(PS)与有机发光材料聚乙烯咔唑(PVK)和八羟基喹啉(Alq3)的复合，研究了PS／(PVK，Alq3)复合体系的光学性能和电学性能。PL谱的测试发现，PS／PVK复合体系的PL同时具有PS和PVK的峰；在485nm的位置出现了1个新峰，讨论了这个峰的来源。研究了n型单晶Si制备的PS与PVK复合(n-PS／p-PVK)和P型单晶Si制备的Alq3复合(p-PS／n-Alq3)后的}y特性。测试表明，这两个复合体系的I-V曲线都显示了良好的整流特性。结果表明，PS／(PVK，Alq3)复合体系适合用来制备PS基的发光二极管。最后借助无机半导体的能带理论对此进行了分析。     

Photorefractive behaviors in a polymer composite including layered silicates

Photorefractive (PR) behavior was observed in a polymer nanocomposite system. The composite is made up of poly(N-vinylcarbazole) (PVK), 2,4,7-trinitro-9-fluorenone (TNF), 4-(4-nitrophenylazo)aniline (DO3), and 9-ethylcarbazole (ECZ), with or without Montmorillonite (MMT) or laponite as a layered silicate. The structures of nanocomposite-PR samples were investigated by X-ray diffraction (XRD). To investigate the PR property, two-beam coupling (TBC) and four-wave mixing experiments were performed. The gain coefficients of the MMT-based nanocomposite-PR system are somewhat lower than that of the unfilled system. However, the equilibrium normalized final diffracted signal of PR-nanocomposite is higher than the unfilled PR sample. Furthermore, by adding laponite instead of MMT to the polymeric PR system, the gain coefficient increases to the original value of the unfilled system by reducing the light scattering, so that it can be said that the memory stability is greatly enhanced in grating decay behavior.     

Modifications of carbon for polymer composites and nanocomposites

The various forms of carbon used in composite preparation include mainly carbon-black, carbon nanotubes and nanofibers, graphite and fullerenes. This review presents a detailed literature survey on the various modifications of the carbon nanostructures for nanocomposite preparation focusing upon the works published in the last decade. The modifications of each form of carbon are considered, with a compilation of structure-property relationships of carbon-based polymer nanocomposites. Modifications in both bulk and surface modifications have been reviewed, with comparison of their mechanical, thermal, electrical and barrier properties. A synopsis of the applications of these advanced materials is presented, pointing out gaps to motivate potential research in this field.     

Bactericidal and Anticorrosion Properties in PVK/MWNT Nanocomposite Coatings on Stainless Steel

A PVK/MWNT nanocomposite coating on stainless steel is developed and tested for antimicrobial and anticorrosion properties. The coating is prepared via electrochemical deposition onto SS surfaces and is monitored using cyclic voltammetry. High‐resolution XPS measurements of the C 1s and N 1s regions are used to estimate the film composition. AFM shows a homogeneous thin film of several µm thickness with well‐defined globular domains. The bactericidal functionality of the electrodeposited film is demonstrated by its antibacterial activity against Escherichia coli, even with low MWNT loading (≈6%). The excellent anticorrosion property of the coating is demonstrated after 7 d of exposure to NaCl (0.5 M ) solution.

     

Dispersion polymerization of NVCA in compressed liquid dimethyl ether in the presence of PDMS-g-pyrrolidone carboxylic acid: Effects of initiators

Dispersion polymerization of N-vinylcarbazole (NVCA) was performed in compressed liquid dimethyl ether with PDMS-g-pyrrolidonecarboxylic acid (Monasil PCA™) as the surfactant and with 2,2′-azobis(2,4-Dimethylvaleronitrile) (V-65), 2,2-azobisisobutyronitrile (V-60) (AIBN) and dimethyl 2,2′-Azobis(isobutyrate) (V-601) as the initiators. The effects of polymerization temperature, initiator types and initiator concentration were investigated. Spherical poly(N-vinylcarbazole) (PVK) particles were produced, even at 40 °C, by the low-temperature initiator, 2,2′-azobis(2,4-Dimethylvaleronitrile) (V-65). Through low-temperature polymerization with V-65, we successfully obtained high molecular weight PVK.     

A novel organic electrical memory device based on the metallofullerene-grafted polymer (Gd@C82-PVK)

The ITO/Gd@C₈₂-PVK/Al sandwich nonvolatile memory device was developed based on polymer containing carbazole moieties as electron donors and Gd@C₈₂ as electron acceptors for the first time. The results of I–V characteristic test indicated that the new material exhibited typical bistable electrical switching and a nonvolatile rewritable memory effect, with a turn-on voltage of about −1.5 V and an ON/OFF-state current ratio of more than 10⁴. We propose that such a low turn-on voltage is caused due to the encaged metal and the DFT calculation indicated that the encaged metal served as an important electron trapping center, which facilitated the arrival of turn-on voltage.     

Photorefraetive Effect in a CdS Nanoparticles- sensitized Polymer Composite

The photorefractive （PR） performance of an organic/inorganic hybrid polymer composite sensitized by CdS nanoparticles, combining poly（N-vinylcarbazole） （PVK）, the second-order optically nonlinear chromophore 1-n-butoxy-2-methyl-（4-p-nitropheylazo）benzene （BMNPAB） and 9-ethylcarbazole （ECZ） was studied. It was confirmed that the CdS colloidal particles had a nanoscale size and quantum confinement effect adopting transmission electron microscopy and UV-Vis absorption spectroscopy. The addition of CdS nanoparticles as a photosensitizer in PVK will be significant enhancement of photoconductivity because of the high photocharge generation quantum efficiency and high charge transport to conducting polymer. The polymer composite film exhibited PR effect with a method of two-beam coupling experiment. And an asymmetric two. beam coupling gain of 45.8 cm^-1 without applied electric filed is obtained at 632.8 nm wavelength.