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Shear alignment of the block copolymer (BCP) thin film is one of the promising directed self-assembly (DSA) methodologies for the unidirectional alignment of sub-10 nm microdomains of BCPs for next-generation nanolithography and nanowire-grid polarizers. However, because of the differences in the surface/interfacial energies at the top surface/bottom interface, the shear-induced ordering of BCP nanopatterns has been restricted to BCPs with spherical and cylindrical nanopatterns and cannot be realized for high-aspect-ratio perpendicular lamellar structures, which is essential for practical application to semiconductor pattern processes. It is still a difficult challenge to fabricate the unidirectional alignment in a short time over a large area. In this study, we propose an approach for combining the shear-rolling process with the filtered plasma treatment of BCP films for the fabrication of unidirectionally aligned and perpendicularly oriented lamellar nanostructures. This approach enables fabrication within 1 min on a 4 in scale. We treated filtered plasma on the BCP film for perpendicular orientation and executed the hot-rolling process with different roller and stage speeds. Large-scale shear was generated only at the location where the BCP film was in contact with both the roller and stage, effectively applying shear stress to a large area of the BCP film within a short time. The repeated application of this shear-rolling process can achieve a higher level of unidirectional alignment. Our aligned BCP vertical lamellae were used to fabricate a high-aspect-ratio sub-10-nm-wide metallic nanowire array via dry/wet processes. In addition, shear-rolling with chemoepitaxy patterns can achieve higher orientational order and lower defectivity.

We fabricated a titanium oxide (TiO2) resistive memory device utilized to naturally erasable device with a simple cross-bar array structure inhibiting sneak paths using selecting property. The Al/TiO2/Al memory device showed conventional nonvolatile and bipolar resistive switching properties with a vacancy-based drift conduction procedure. The conducting filament could be removed through redistribution of the oxygen vacancy to the active bulk region resulting in self-erasable properties, which have made it possible to guide unwanted information to be removed naturally. This self-erasable memory device has the potential to be utilized for the storage of susceptible information which should be eliminated after a sufficient length of time.

Nonfullerene acceptors have played a critical role in achieving record efficiency of organic photovoltaic (OPV) devices, and ITIC-based materials are an important type of nonfullerene acceptor. Herein, we developed new interlayer polymers for nonfullerene acceptor-based OPVs: PDMA(N)EMA and PDMA (N–O)EMA. In particular, PDMA(N)EMA effectively lowered the work function at the interface with the bulk heterojunction active layer and thus enabled efficient electron collection by the OPV device. Therefore, the OPV device incorporating PDMA(N)EMA showed a power conversion efficiency (PCE) of 8.19%, which was substantially enhanced compared with the 4.54% PCE of an ethoxylated polyethylenimine (PEIE)-based device. Whereas PEIE chemically attacked ITIC and degraded the performance of the OPV device, the PDMA(N)EMA formed a stable interface with ITIC, resulting in a dramatic increase of the VOC of the PDMA(N)EMA-based devices. Furthermore, the suppression of degradation at the PDMA(N)EMA interface also improved device stability at elevated temperatures. This work highlights the importance of the design and development of appropriate interlayer materials for realizing stable and high-efficiency nonfullerene-based OPVs.

We report the synthesis of a new low band gap planar polymer of poly(2,5-bis(2-decyltetradecyl)-3-(5-(dithieno[3,2-b:2′,3′-d]thiophen-2-yl)thieno[3,2-b]thiophen-2-yl)-6-(thieno[3,2-b]thiophen-2-yl)-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione) (PTTDPP-DT-DTT) for use in organic thin film transistors (OTFTs). The polymer backbone is highly planar and well-conjugated, facilitating interchain stacking. The PTTDPP-DT-DTT-based OTFTs were fabricated and carrier mobilities were improved by using a binary solvent system: chloroform (CF):toluene (Tol), CF:chlorobenzene (CB), and CF:o-dichlorobenzene (DCB). The addition of higher boiling point solvents promoted film crystallinity with more edge-on orientations. Thus, the use of CF:DCB yielded the highest carrier mobility obtained among the devices tested. Thermal annealing further enhanced the mobility of the CF:DCB device. Atomic force microscopy images disclosed the most fibrous feature in the thermally annealed polymer film cast from CF:DCB solution. This work highlights that both the proper selection of a binary solvent and thermal annealing can manage film morphology of rigid planar conjugated polymer semiconductors effectively for high-performance OTFTs.

CdSe/Zn1-X CdX S core/shell heterostructured quantum dots (QDs) with varying shell thicknesses are studied as the active material in a series of electroluminescent devices. "Giant" CdSe/Zn1-X CdX S QDs (e.g., CdSe core radius of 2 nm and Zn1-X CdX S shell thickness of 6.3 nm) demonstrate a high device efficiency (peak EQE = 7.4%) and a record-high brightness (>100 000 cd m(-2) ) of deep-red emission, along with improved device stability.

There is rising demand for metal or metal oxide nanoparticle (NP)/polymer nanocomposite films with desired functionalities. However, it is difficult to directly combine well-defined NPs synthesized using organic fatty acids in nonpolar media with water-soluble polymers, except polyelectrolytes with specific functional moieties, because they differ in their hydrophobic/hydrophilic properties. We have developed a facile and universal hydrophilic/hydrophobic layer-by-layer (LbL) assembly method that enables perfect nanoblending between water-soluble polymers and hydrophobic NPs, maintaining their specific functionalities. Various hydrophobic NPs stabilized by using oleic acid (OA) (e.g., OA-TiO2, OA-Fe3O4, OA-Ag, and OA-Pt NPs) were directly LbL assembled with various water-soluble polymers (including biomaterials) containing carboxylic acid (–COOH), tertiary ammonium (N+), hydroxyl (–OH), and/or ether (–O–) groups. This adsorption behavior is based on the affinities between water-soluble polymers with multidentate binding sites and the surfaces of metal or metal oxide NPs stabilized by OA ligands. Our approach can be used to fabricate unipolar switching nonvolatile memory devices with ON/OFF current ratios greater than ∼1010 and good memory stability, despite the use of water-soluble polymers.

Thick inorganic shells endow colloidal nanocrystals (NCs) with enhanced photochemical stability and suppression of photoluminescence intermittency (also known as blinking). However, the progress of using thick-shell heterostructure NCs in applications has been limited due to the low photoluminescence quantum yield (PL QY ≤ 60%) at room temperature. Here, we demonstrate thick-shell NCs with CdS/CdSe/CdS seed/spherical quantum well/shell (SQW) geometry that exhibit near-unity PL QY at room temperature and suppression of blinking. In SQW NCs, the lattice mismatch is diminished between the emissive CdSe layer and the surrounding CdS layers as a result of coherent strain, which suppresses the formation of misfit defects and consequently permits ∼100% PL QY for SQW NCs with a thick CdS shell (≥5 nm). High PL QY of thick-shell SQW NCs is preserved even in concentrated dispersion and in film under thermal stress, which makes them promising candidates for applications in solid-state lightings and luminescent solar concentrators.

Despite a large number of developments of noble metal (or metal oxide) NP-based catalysts, it has been a great challenge to prepare high-performance recyclable catalysts with integrated functionalities that can be used in various solvent media. Here, we report on layer-by-layer (LbL) assembled multicatalysts with high catalytic performance, showing high dispersion and recycling stability in organic and aqueous media. The remarkable advantages of our approach are as follows. (i) Various metal or metal oxide NPs with desired catalytic performance can be easily incorporated into multilayered shells, forming densely packed arrays that allow one colloid to be used as a multicatalyst with highly integrated and controllable catalytic properties. (ii) Additionally, the dispersion stability of catalytic colloids in a desired solvent can be determined by the type of ultrathin outermost layer coating each colloid. (iii) Lastly, the covalent bonding between inorganic NPs and dendrimers within multilayer shells enhances the recycling stability of multicatalytic colloids. The resulting core-shell colloids including OA-Fe3O4 NPs, TOABr-Pd NPs, and OA-TiO2 NPs exhibited excellent performance in the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and photocatalysis in aqueous media and in the Sonogashira coupling reaction (99% yield) in organic media. Given that the catalytic properties of recyclable colloids reported to date have entirely depended on the functionality of a single catalytic NP layer deposited onto colloids in selective solvent media, our approach provides a basis for the design and exploitation of high-performance recyclable colloids with integrated multicatalytic properties and high dispersion stability in a variety of solvents.

We demonstrate that voltage-independent and highly efficient white light-emitting diodes (WLED) can be obtained based on phosphorescent dye-doped conjugated polymer blend films. Conjugated polymers are used as the blue and green emitters, as well as the energy host, and a phosphorescent dye is used as the red emitter and guest material. The phase-separation between the conjugated polymers is suppressed by blending miscible polymer and copolymer having the same moiety. Therefore, we expect that efficient Forster-type energy transfer occurs through this homogeneous morphology. By introducing the copolymer into the emissive layer to enhance its miscibility, we obtained a voltage-invariant white emission from the polymeric LEDs. The luminous efficiency of the WLED with the single active layer is increased dramatically by introducing the phosphorescent dopant as a red emitter.

The work presented here focuses on the preparation and characterization of gate dielectrics in organic thin-film transistors (OTFTs), fabricated by the sol–gel process. Hybrid dielectrics were prepared with acryl UV resin, titanium n-butoxide, catalytic HCl, and acetylacetone by sol–gel process and patterned by UV cross-linking below 120 °C. Leakage currents of dielectric layers remained below 10−9 A under operating voltage and dielectric constants were measured to be ∼6.5 at 10 kHz. The field effect mobility and on–off ratio were ∼0.86 cm2/V s and ∼104, respectively. These results demonstrate that sol–gel hybrid systems are suitable for gate dielectrics in OTFTs.

High efficiency organic light-emitting-devices (OLED) have been fabricated by incorporation of a polymeric layer as a controller of the unbalanced charge. In device configuration of ITO/PEDOT:PSS/PVK/Alq3/LiF:Al, poly(N-vinylcarbazole) (PVK) was selected as a block-ing layer (BL) because it has a hole transporting property and a higher band gap, especially a lower LUMO level than the emitting layer (Alq3) and a higher HOMO level than the hole injection layer (PEDOT: PSS). As a result, the optimal structure with this bl layer showed a peak efficiency of 6.89 cd/A and 2.30 lm/W compared to the device without the PVK layer of 1.08 cd/A, 0.27 lm/W. This result shows that the PVK layer could effec-tively block the electrons from metal cathode and confine them in the emitting layer and accomplish the charge balance, which leads to enhanced hole-electron balance for achieving high recombination efficiency.

We investigate the effect of a UV-irradiated poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) buffer layer on the performance of polymer photovoltaic cells based on poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) blends. It was found that UV irradiation can reduce the bulk and contact resistance of PEDOT:PSS films, improving the power conversion efficiency from (3.05 ± 0.04)% to (3.50 ± 0.03)% due to the lower device series resistance under an illumination of AM1.5G, 100 mW/cm2. The work function change after UV irradiation and negligible surface morphology change was noticed.

Ultrahigh density arrays of conducting polypyrrole (PPy) nanorods are fabricated directly on the indium-tin oxide coated glass by an electropolymerization within a porous diblock copolymer template. The nanorods are shown to have conductivity much higher than thin PPy films, due to the high degree of chain orientation, even though the separation distance for two neighboring PPy main chains is as small as 0.37 nm. The ultrahigh density arrays of conducting polymer nanorods have potential applications as sensor materials, nanoactuators, and organic photovoltaic devices.

A sensor was made using Au/Cr electrodes on a glass substrate and a thin carbon multiwall nanotube film printed between them. A bias-heating method was used completely to desorb gas molecules and restore its initial conductance. The temperature of the thin carbon nanotube film varied depending on the magnitude of the voltage used, and this relationship was investigated. After being used to detect NO 2 , the sensor returned to its initial conductance. This method enables complete recovery without additional processing steps, such as the fabrication of heat structure and ambient heating.

In this work, we fabricated white organic light-emitting devices (WOLEDs) containing a layered light-emitting region composed of a single blue-emitting host and different fluorescent dopant materials. The effects of varying the dye-doping ratio and emitting layer thickness on the efficiency, lifetime, spectral voltage-dependence and white balance were investigated for devices with a blue/orange stacked layer structure. Addition of a blue host layer doped with a green-emitting dopant, to give a blue/green/orange emitter, resulted in a broadband white spectrum without the need for a charge-blocking interlayer. The composition of blue, green and orange dopants in the host and the thickness of each emitting layer were optimized, resulting in a device efficiency of 9–11 cd A−1 even at a high brightness of 10 000 cd m−2 (achieved at a bias voltage of less than 9 V) with an emission spectrum suitable for lighting applications.

We demonstrate white organic light-emitting diodes (OLEDs) by exciplex formation at organic solid-state interface between a charge transport layer and an emitting layer. White OLEDs have complementary emitters with an emission peak of 400 nm around the near-ultraviolet, and an emission peak of 580 producing a yellow color. The EL spectra of the white OLEDs have shown a covering through visual range from 400 to 780 nm. The CIE coordinate of the emitted light was (0.34, 0.34) with low driving current density (8.6 mA/cm2) and high efficiency (12 cd/A, 2 lm/W) at 1 000 cd/m2.

Pentacene-based organic thin-film transistors (TFTs) have been fabricated with and without treatment by hydrogen (H2) plasma at the interface between the electrode and the pentacene surface. Processing with a H2 plasma was carried out in a plasma-enhanced chemical vapor deposition with varying treatment times. The interface treatment by H2 plasma resulted in improved device electrical properties. Removal of oxygen from the pentacene surface occurs due to slight etching by the plasma. Sufficient flux density of the H2 plasma leads to full pentacene-surface coverage by rearranging the hydrogen with carbon instead of oxygen. Atomic force microscopy profiles reveal the morphology changes of the pentacene surface after treatment, and secondary ion mass spectrometry shows the change via compositional depth profiles indicating H2 , O2, and C-H binding. Hydrogen treatment, therefore, appears to modify the interface by removing the surface oxygen layer, resulting in better performance of the organic TFT

Pentacene thin film transistors fabricated without photolithographic patterning were fabricated on the plastic substrates. Both the organic/inorganic thin films and metallic electrode were patterned by shifting the position of the shadow-mask which accompanies the substrate throughout the deposition process. By using an optically transparent zirconium oxide (ZrO2) as a gate insulator and octadecyltrimethoxysilane (OTMS) as an organic molecule for self-assembled monolayer (SAM) to increase the adhesion between the plastic substrate and gate insulator and the mobility with surface treatment, high-performance transistor with field effect mobility 0.66 cm2/V s and I on/I off > 105 was formed on the plastic substrate. This technique will be applicable to all structure deposited at low temperature and suitable for an easy process for flexible display.

Gas sensors for NO 2 detection were fabricated using printed multiwalled carbon nanotubes (MWCNTs) before and after electric field surface treatment. Printed MWCNTs showed an increase of sensitivity upon exposure to NO 2 and field emission due to vertical alignment and protrusion of CNTs from surface layer after electric field surface treatment. Electron field emission plays a role recovery when exposed to gas molecules in CNT. A Fast recovery time of the printed MWCNT gas sensor was obtained by ohmic heat with a partial field emission effect at room temperature.

A heating process for obtaining free-standing carbon nanotube emitters is presented with the aim of improving field-emission properties from the screen-printed multiwalled carbon nanotube (MWCNT) films. Using an atmosphere with an optimum combination of nitrogen and air for heat treatment of CNT films, the CNT emitters can be made to protrude from the surface. This allows for a high emission current and the formation of very uniform emission sites without special surface treatment. The morphological change of the CNT film by this technique has eliminated additional processing steps, such as surface treatment which may result in secondary contamination and damage to the film. Despite its simplicity the process provides a high reproducibility in emission current density which makes the films suitable for practical applications.

The characteristics of perylene acid sensitized tin oxide photovoltaic device with gel polymer system made of a free standing film of poly(vinylidene fluoride-co-hexafluoropropylene) as an solid-state electrolyte were studied. The photovoltaic device composed of ITO/perylene Acid-SnO 2 /gel polymer electrolyte/Pt structure showed a short circuit photocurrent density of 2.5 mA/cm 2 , an open circuit photovoltage of 0.28 V, a fill factor of 0.51 and an overall power efficiency of 0.36% under illumination of white Xe light with an intensity of 100 mW/cm 2 . The influence of plasticizer additive on the ionic conductivity of gel polymer electrolyte was also studied.

We describe the synthesis and luminescence characterization of conjugated dendrimers with triazine peripheries and a distyrylanthracene core that are suitable for electroluminescence applications. The dendrimers consist of dendritic triazine wedges with high electron affinity, stilbene branches, and a distyrylanthracene core as an emitting moiety. The dendrimers have lowest unoccupied molecular orbital values of about −2.7 eV. Photoluminescence studies have indicated that a cascade energy transfer occurs from the triazine wedges to the stilbene bridges and finally to the distyrylanthracene core. Thus, the emission wavelength is determined by the distyrylanthracene core unit. The energy-transfer efficiency of the distyrylanthracene-cored dendrimers is about 47 and 20% for the first and second generations, respectively. A preliminary electroluminescence property investigation has also been conducted. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 5855–5862, 2006

Poly( p -phenylene vinylene) has studied as not only emissive material but also hole transporting material in light-emitting diodes. Because PPV is non-soluble polymer at any solvent, it can be used as hole transporting layer (HTL) in multilayer structure of electroluminescent devices. After thermal conversion of PPV precursor into PPV, we spin-coated polydioctylfluorene (PDOF) as emitting layer on it. EL devices using the PPV doped with organic salts, tetra- n -butylammonium tetrafluoroborate (TBABF 4 ), as HTL showed great luminance efficiency. The organic salts in PPV polymer chains formed local dipoles under the electrical field and it affected the performance of the EL devices.

New electrophosphorescent organic light-emitting diodes were fabricated by polymer/Ir(ppy)3 bilayers. Already several groups have reported polymer systems that show efficient energy transfer from a polymer host to an organometallic guest. We have fabricated a phosphorescent polymer light-emitting device with fac tris(2-phenylpyridine)iridium [Ir(ppy)3] as a triplet emissive layer on a poly(vinylcarbazole) (PVK) layer. The emission spectrum of the bilayer device exhibited pure Ir(ppy)3 emission, which indicates that the efficient energy transfer from PVK layer to Ir(ppy)3 layer. Our bilayer device system shows a lower driving voltage and a higher current density than those of the general blended device. � 2005 Elsevier B.V. All rights reserved. PACS: 85.60.J

White light emission was obtained from a light-emitting diodes (LEDs) prepared from an immiscible polymer blend consisting of poly(9,9′-dihexylfluorene-2,7-divinylene-m-phenylenevinylene-stat-p-phenylenevinylene) (PDHFPPV) and poly(2-methoxy-5-(2′-ethy-hexyloxy)-1,4-phenylenevinylene) (MEH-PPV). An inefficient energy transfer between PDHFPPV and MEH-PPV was observed because the blends are partially miscible. More importantly, because the order of bandgap energy is PVK > PDHFPPV > MEH-PPV we observed pure and strong white emission from this PLEDs, which results from the efficient Forster-type energy transfer from PVK to PDHFPPV and the partial energy transfer from PDHFPPV to MEH-PPV. The ITO/(PVK/immiscible blend)/Li:Al devices showed more enhanced white-light output compared with that of the ITO/(immiscible blend)/Li:Al device.

Efficient white-light-emitting diodes (WLEDs) have been developed using a polyfluorene-type blue-emitting conjugated polymer doped with green and red phosphorescent dyes. The emission spectrum of the conjugated polymer, which has a very high luminescent efficiency, shows a large spectral overlap with the absorbance of green and red iridium complexes. Also, efficient energy transfer from the conjugated polymer to the iridium complexes is observed. Poly(N-vinyl carbazole) is used to improve the miscibility between conjugated polymer and iridium complexes because of their poor chemical compatibility and phase separation. A white emission spectrum is easily obtained by varying the contents of the three materials and controlling the phase morphology. Moreover, these WLEDs show a voltage-independent electroluminescence owing to the threshold and driving voltage of the three materials being similar as a result of energy transfer.

Double-walled carbon nanotubes (DWCNTs) were synthesized by catalytic chemical vapor deposition using Fe-Mo/MgO as a catalyst at 1000 degrees C under the mixture of methane and hydrogen gas. The nanotubes were purified by acid but were not damaged. Thermogravimetric analysis revealed the purity of the tubes to be about 90%. The high-resolution transmission electron microscopy image showed that DWCNTs have inner tube diameters of 1.4-2.6 nm and outer tube diameters of 2.3-3.4 nm. We observed radial breathing modes in Raman spectra, which are related to the diameter of inner nanotubes. The purified DWCNTs were mixed with organic vehicles and glass frit, and then they were screen-printed on glass substrate coated with indium tin oxide. The field emission properties of the screen-printed DWCNT films were examined by varying the amount of glass frit ingredient within the DWCNT paste. The results showed that DWCNT emitters had good emission properties such as turn-on field of 1.33-1.78 V/microm and high brightness. When the applied anode voltage was gradually increased, current density and brightness became saturated. We also observed DWCNTs adsorbed on the anode plate; they were DWCNTs peeled off from the cathode plate for field emission measurement.

Influence of charge mobility of n-type organic semiconductors for the performance of organic p-n junction type photovoltaic devices has been studied. Two n-type organic semiconductors with same main moiety (i.e., perylenebiscarboximide derivates), which posses similar HOMO, LUMO and band gaps; however with different charge mobility especially electron mobility have been utilized in this study. The electron mobility was measured by time of flight method. The electron mobility difference was caused by molecular packing characteristics since one of the semiconductor showed a liquid crystalline behavior.

In this paper we report a technology for lightweight, small radio-frequency (rf) microelectromechanical system packaging with a short electrical path length. We used an ultrathin silicon substrate as the packaging substrate. Via holes for vertical feed-through were fabricated on the thin silicon wafer. Then, bottom-up gold electroplating was applied to fill via holes. For hermetic sealing, gold-gold direct metal bonding was used in the sealing line. The packaged rf device has a reflection loss below -22 dB and an insertion loss of -0.05 to -0.08 dB. Therefore, with the ultrathin silicon wafer, a lightweight, small device package can be constructed.

Fluorescent polymer and poly (sodium 4-styrenesulfonate) ionomer (PSS-ionomer) blends were used as emitting layers in polymer light-emitting diodes (LEDs). The two polymers were blended in the optimal ratio which shows the highest luminescent intensity due to dilution effect. We changed the ionic contents of ionomer from 5 mol% to 10 mol% with fixed optimal blended ratio. We obtained the narrow spectrum having high color purity in the blend system. The conjugated polymer/PSS-ionomer blend devices achieved a more enhanced luminescent efficiency as compared with that of the conjugated polymer/PS device due to polar groups in the PSS-ionomer, which enhance the electron injection from the cathode to the emitting molecules.

In this paper, we describe a new approach for fabrication of high efficient polymeric light-emitting diodes (PLEDs). In the device configuration of ITO/HTL/EBL/EML/BaF2:Ca:Al (ITO: indium tin oxide, HTL: hole transport layer, EBL: electron blocking layer, EML: emitting layer), EBL contains cross-linkable moieties in order to make the layer which is insoluble to layering of an additional emitting polymer. The devices with EBL exhibit strong blue emissions and higher efficiency values than those in devices without EBL. The synthesis, characterization, device fabrication, and electroluminescence (EL) properties of devices will be presented.

This paper presents heating process for obtaining standing carbon nanotube emitters to improve field‐emission properties from the screen‐printed multiwalled carbon nanotube (MWCNT) films. In an atmosphere with optimum combination of nitrogen and air for heat treatment of CNT films, the CNT emitters can be made to protrude from the surface. This allows for high emission current and the formation of very uniform emission sites without special surface treatment. The morphological change of the CNT film by this technique has eliminated additional processing steps, such as surface treatment which may result in secondary contamination and damage to the film. Despite its simplicity the process provides high reproducibility in emission current density which makes the films suitable for practical applications.

Currently, the flexible organic light emitting devices (OLEDs) are investigated. They are very vulnerable to moisture, and thus have been found to show some problems. Thus, an effective barrier layer is needed to protect from moisture in air. We deposited thin films with magnesium oxide (MgO) and silicon oxide (SiO2) compounds mixed at various mixture ratios on flexible polyether sulfone (PES) substrates by an electron‐beam evaporator to investigate their applizability for transparent barrier applications. In this study, we found that as the MgO fraction increased, thin films comprised of MgO and SiO2 compounds became more amorphous and their surface morphologies become smoother and denser. In addition, zirconium oxide (ZrO2) was added to the above‐mentioned compound mixtures. ZrO2 made thin mixture films more amorphous and made the surface morphology denser and more uniform. The water vapor transmission rates (WVTRs) of the whole films decreased rapidly. The best WVTR was obtained by depositing ...

Insertion of a thin lithium fluoride (TLF) layer between an emitting layer (EML) and an electron transporting layer has resumed in the developement of a highly efficient and bright organic light‐emitting diode (OLED). Comparing with the performance of the device as a function of position with the TLF layer in tris‐(8‐hydroxyquinoline) aluminum (Alq3), we propose the optimal position for the TLF layer in the stacked structure. The fabricated OLED shows a luminance efficiency of more than 20 cd/A, a power efficiency of 12 lm/W (at 20 mA/cm2), and a luminance of more than 22 000 cd/m2 (at 100 mA/cm2), respectively. We suggest that the enhanced performance of the OLED is probably attributed to the improvement of carrier balance to achieve a high level of recombination efficiency in an EML.

The energy transfer process upon photoexcitation in binary polymer blends with different donor/acceptor pairs were investigated with the aid of the steady-state and time-resolved photoluminescence methods. The observed differences in the energy transfer effi- ciency are not fully explained by the Forster radius, deduced from the spectral overlap calculation. The order of energy transfer efficiencies for different donor/acceptor pairs does not follow the sequence of Forster radius, particularly for the acceptors having relatively long PL lifetimes. Hence, an alternative simple model is proposed to account for the order of energy transfer efficiency, which is to include the effect of the acceptor PL lifetime, specifically in the presence of excess donor. Such is the case with usual polymer LED devices.

The effect of improvement on the surface morphology of screen‐printed carbon nanotube (CNT) films was studied by using the optically clear poly‐dimethylsiloxane (PDMS) elastomer for surface treatment. After the PDMS activation treatment was applied to the diode‐type CNT cathode, the entangled carbon nanotube (CNT) bundles were broken up into individual free standing nanotubes to remarkably improve the field‐emission characteristics over the as‐deposited CNT film. Also, the cathode film morphology of a top gated triode‐type structure can be treated by using the proposed surface treatment technique, which is a low‐cost process, simple process. The relative uniform emission image showed high brightness with a high anode current. This result shows the possibility of using this technique for surface treatment of large‐size field emission displays (FEDs) in the future.

Thin films with magnesium oxide (MgO) and silicon oxide (SiO2) compounds mixed at various mixture ratios were deposited on flexible polyether sulfone (PES) substrates by an e-beam evaporator to investigate their potential for transparent barrier applications. In this study, as the MgO fraction increased, thin films comprising MgO and SiO2 compounds became more amorphous, and their surface morphologies became smoother and denser. In addition, zirconium oxide (ZrO2) was added to the above-mentioned compound mixtures, and the properties of the compound mixture comprising MgSiZrO were then measured. ZrO2 made the thin mixture films more amorphous, and made the surface morphology denser and more uniform. Whole thin films of 250 ± 30 nm in thickness were formed, and their water vapor transmission rates (WVTRs) decreased rapidly. The best WVTR was obtained by depositing thin films of MgSiZrO compound among the whole thin films. The WVTRs of the PES substrate in the bare state decreased from 47 to 0.8 g m−2 day−1. This MgSiZrO compound was deposited on polyethylene terephtalate (PET) substrates again to confirm the availability of the compound mixture. Thin films on the PET substrates decreased the WVTRs remarkably from 2.96 to 0.01 g m−2 day−1. These results were similar to those of thin films on PES substrates. As the thin mixture films became more amorphous and surface morphology denser and more uniform, the WVTRs decreased. Therefore, the thin mixture films became more suitable for flexible organic light emitting displays (OLEDs) as transparent passivation layers against moisture in air. Copyright © 2006 John Wiley & Sons, Ltd.

White light emission was obtained from a light-emitting diode prepared from polymer/quantum dot nanocomposites consisting of poly(9,9′-dihexylfluorene-2,7-divinylene-m-phenylenevinylene-stat-p-phenylenevinylene) (PDHFPPV) and CdSe nanoparticles. Blue emission from PDHFPPV and red emission from the nanoparticles, which is triggered by partial excitation energy transfer from PDHFPPV, jointly contribute to white emission of the organic/inorganic hybrid device. Also, the blue-emitting matrix polymer makes the device preparation process simpler due to its high processability. By controlling the blend ratio, we could obtain a pure white color from the hybrid device.

N , N ′-diphenylbutyl-3,4,9,10-perylenebiscarboximide (PTCDI-C4Ph) were characterized by optical and electrochemical methods. A device with an ITO/PTCDI-C4Ph (≈2 μm)/Al structure was fabricated to measure mobility by time-of-flight techniques. This vacuum deposited organic layer was an amorphous state. Electrons were observed faster than holes. The electron and hole mobilities were 1.8 × 10 −4 cm 2 /V s and 1.1 × 10 −4 cm 2 /V s under the electric field of 500 (V/cm) 1/2 , respectively. This result shows that this organic compound is a good candidate for an n-type conduction.

Photo-oxidation plays an important role in the lifetime of PLEDs fabricated from PFs. In addition, most of these PLEDs suffer from a degradation of the device under operation; the degradation is documented in the formation of a low-energy emission band at 2.2–2.3 eV, which turns the desired blue emission color into an undesired blue-green emission. With the aim of simultaneously overcoming all these drawbacks, a blue light-emitting polymer/mesoporous silica nanocomposite was prepared by blending poly(9,9-dioctylfluorene) with surface modified nanoporous silica. This nanocomposite film shows dramatically increased photo-stability and color purity.

We have fabricated a white polymer light-emitting-diode bilayer structure that contains a ternary polymer blend. The first layer of poly(9-vinylcarbazole) acts as an energy donor and electron blocker, and the second layer comprising an immiscible polymer blend of two light-emitting polymers, poly(9,9 0 -dihexylfluorene-2,7-divinylene-m-phenylenevinylene-stat-p-phenylenevinylene) and poly(2-methoxy-5-(2 0 -ethyl-hexyloxy)-1,4-phenylenevinylene), emits light. The emissive white color of the device was observed to be practically independent of the driving voltage (near CIE coordinate; 0.33, 0.33). In addition, it shows greatly enhanced luminous efficiency compared to a ternary blended white light-emitting-diode. � 2005 Elsevier B.V. All rights reserved.

We have synthesized conjugated dendrimer with triazine peripheries, and their luminescence properties were investigated. The dendrimers consist of dendritic triazine wedges for electron transport, distyrylbenzene core as an emitting moiety, and t-butyl peripheral groups for good processing properties. The dendrimers have LUMO values of about −2.7 eV possibly because of the triazine moiety with high electron affinity. Photoluminescence study indicates that energy transfer occurs from the triazine wedges to the stilbene bridge, and finally to the core chromophore units due to a cascade decrease of bandgap from the peripheral wedge to core moiety. Therefore, the emission wavelength was determined by the structure of the core unit. The energy transfer efficiency of distyrylbenzene-cored dendrimers was about 75 and 55% for Trz-1GD-DSB and Trz-2GD-DSB, respectively. A preliminary electroluminescence property also was investigated. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 254–263, 2006

Characteristics of ITO/polypyrrole (PPy) nano fibers/poly(3-hexylthiophene)/Al photovoltaic devices prepared by nano template method were studied. PPy nano fibers on ITO glass were formed through nano pores of polymer membrane template using home made special sample holder by electrochemical polymerization in an electrolyte solution of pyrrole and lithium perchlorate as a dopant in acetonitrile. Ordered structure with enhanced interfacial area formed by nano template method enable to fabricate polymeric photovoltaic device with improved photo-conversion efficiency. This nano fiber structures film possesses increased interfacial area, large charge separation area (photoactive zone) and secured charge transportation route. The effect of altering energy levels of PPy by changing doped state was also studied. Device made with nano fiber structure showed enhanced photovoltaic effect than that of overlayed film device.

By applying a critical field treatment instead of the conventional surface treatments such as soft rubber roller, ion beam irradiation, adhesive taping, and laser irradiation, electron emission properties of screen‐printed carbon nanotubes (CNTs) were enhanced and investigated based on the emission current‐voltage characteristics through scanning electron microscopy. After nanotube emitters were activated at the applied electric‐field of 2.5 V/um, the electron emission current density with good uniform emission sites reached the value of 2.13 mA/cm2, which is 400 times higher than that of the untreated sample, and the turn‐on voltage decreased markedly from 700 to 460 V. In addition, enhancement of the alignment of CNTs to the vertical direction was observed.

We synthesized a star copolymer of poly(vinylcarbazole) (PVK) branched from a fullerene (C60) center, and investigated its optical absorption and photoluminescence properties. The chemically hybridized PVK-C60 was then employed as a hole-transporting layer of the electroluminescent device with a poly(9,9′-dihexylfluorene-2,7-divinylene-m-phenylenevinylene-stat-p-phenylenevinylene) (CPDHFPV) emitting layer. The ITO/PVK-C60/CPDHFPV/LiF/Al device showed a strong electroluminescence quenching due to a direct contact of the PVK-C60 and the CPDHFPV layers. In contrast, when an additional PVK layer was introduced between the two layers, the electroluminescence was largely enhanced. The emitted light power of the ITO/PVK-C60/PVK/CPDHFPV/LiF/Al device was improved by ∼3 times compared with the device without the PVK-C60 layer.