Fabrication and implementation of large-area organic light-emitting-diode devices on direct patterned backplanes

In this paper, we report on a new cost-effective fabrication technology for large-area organic light-emitting diode (OLED) devices that we have developed. We fabricated OLED lighting devices on a directly patterned backplane using a dry process without employing conventional photolithography patterning technology. The indium–tin-oxide (ITO) anode, metal cathode, insulator, and emissive organic layer patterns were all formed directly on the substrates during the sputtering and evaporation steps by using a shadow mask without using etching or lift-off methods. We fabricated and characterized green phosphorescent emission OLED devices with an emission area of 30 × 120 mm², based on backplanes formed by direct patterning technology. Application of direct patterning technology reduced the total number of processing steps to 4 from the 26 steps required by conventional photo-patterning technology, making it possible to reduce large-scale production cost. Although the process steps were reduced considerably, the typical characteristics were comparable to those of photo-patterned OLEDs. Furthermore, the lifetime of the OLEDs based on direct patterned backplane was observed to be 27,200 h, which is approximately 97% of the lifetime of conventionally patterned OLEDs.     

感光性高分子激光全息记录材料的发展

本文对几种新型感光型高分子全息记录材料进行了综述。     

Effects on the field emission properties by variation in surface morphology of patterned photosensitive carbon nanotube paste using organic solvent

Photosensitive carbon nanotube (CNT) paste was prepared by 3-roll milling of multi-walled carbon nanotubes (MWNTs), UV-sensitive binder solution, and Ag as filler additives. Arrays of MWNT dots with a diode structure were fabricated by a combination of screen printing method and photolithography using these paste, and acetone utilized as the developer. The MWNT dots were well-defined and the organic binder materials in the dots were partially removed. The MWNT film without a heat treatment showed a high current density of 1.35 mA/cm² at 3.25 V/μm and low turn-on field of 2.2 V/μm at 100 μA/cm². Acetone can be used as an efficient developer to form patterns and to remove the organic residues in patterns, simultaneously.     

Parallel and serial generated patterned DLC surfaces for creating three-dimensional polymeric stamp structures

This study demonstrates pattern generation on a highly durable and flat diamond-like-carbon (DLC) film with micro/nano-scale resolution using the Atomic Force Microscope (AFM). Parallel processing (masked lithography) and serial local probe processing (maskless lithography) have both been utilized to produce a range of structure shapes at different length scales. The AFM is operated in the electrical conductivity mode which induces oxidation on the DLC surface. The technique offers features with structure depths as small as 20 nm (serial processing) and pattern replication of many centimeters (parallel processing). Moreover parallel processed structures may be further modified via serial patterning using the same instrumentation. As a result, complex shapes can be produced with a depth being controlled by the DLC film thickness and/or by the bias voltage parameters. The patterned DLC structures can be used as a template for fabrication of 3 dimensional polymeric structures.     

Optimization of polymeric host composition for polymer-based electrophosphorescent devices

We have demonstrated an optimized polymeric host material comprising a blend of poly(9-vinylcarbazole) (PVK) and a fluorescent polymer for a highly efficient electrophosphorescence system. Although the chemical compatibility between the blue-emitting-fluorescent polymer and iridium complex, tris[2-phenylpyridine]iridium(III) (Ir-(ppy)₃), is very poor, efficient energy transfers from the blended host to the Ir complex was observed when a small amount of blue-emitting-fluorescent polymer was added to the PVK matrix. The device showed a maximum external quantum efficiency at 5 wt% blue-emitting-fluorescent polymer and 8 wt% Ir complex doping concentrations.     

A photosensitive copolymer for the gate insulator of organic thin-film transistors

A novel cross-linkable copolymer for the gate insulators of organic thin-film transistors (OTFTs) was synthesized by free radical copolymerization with methyl methacrylate and ethylene methylacrylate cinnamoylate. Copolymers of molecular weights (Mn: 109200–160000 g mol⁻¹) and polydispersities (1.59–2.24) were characterized by FTIR and NMR. Spin-coated thin films had smooth surfaces with the root-mean-square (RMS) surface roughness of 0.23 nm, 0.41 nm, respectively, before and after UV irradiation. Exposure of the copolymers to UV light produced cross-linking of the polymeric chains that could be confirmed by comparing the FTIR and UV spectra recorded prior and after irradiation. Moreover, the vanadyl-phthalocyanine (VOPc) OTFTs with the photosensitive copolymer as gate insulator were fabricated and found to exhibit a carrier mobility of 0.25 cm²/V s, an on/off ratio of 10⁴.     

Synthesis of photosensitive poly(methyl methacrylate-co-glycidyl methacrylate) for optical waveguide devices

Photosensitive poly(MMA-co-GMA) for optical waveguide was synthesized, and the refractive index of the polymer film was tuned in the range of 1.481–1.588 at 1550 nm by mixing with bis-phenol-A epoxy resin. The film, which was made by spinning coated the poly(MMA-co-GMA) with photo initiator, had good UV light lithograph sensitivity, high glass transition temperature (T _g : 153°C, after crosslinking) and good thermal stabilities (T _d : up to 324°C, after crosslinking). The optical waveguides with very smooth top surface were fabricated from the resulting polymer by direct UV exposure and chemical development. For waveguides with cladding, the propagation losses of the channel waveguides were measured to be below 3 dB/cm at 1550 nm.     

Improving organic light-emitting diode performance with patterned structures

The influence nano- and micro- structures on light extraction and carrier injection characteristics in organic light-emitting diodes (OLEDs) is examined. The results demonstrate device enhancement from two distinctive patterning scales: embedded microstructure arrays for improved light extraction and imprinted nanostructures for carrier injection enhancement. Further, based on these results, a two-level imprinting stamp is designed which simultaneously produces a micron-sized pattern for facilitating light extraction and a nanometer-sized pattern to improve carrier injection. Additionally, this scalable patterning technology circumvents imprinting misalignment while preserving its compatibility with rollto- roll technology.     

High-damage-threshold static laser beam shaping using optically patterned liquid-crystal devices

Beam shaping of coherent laser beams is demonstrated using liquid crystal (LC) cells with optically patterned pixels. The twist angle of a nematic LC is locally set to either 0 or 90° by an alignment layer prepared via exposure to polarized UV light. The two distinct pixel types induce either no polarization rotation or a 90° polarization rotation, respectively, on a linearly polarized optical field. An LC device placed between polarizers functions as a binary transmission beam shaper with a highly improved damage threshold compared to metal beam shapers. Using a coumarin-based photoalignment layer, various devices have been fabricated and tested, with a measured single-shot nanosecond damage threshold higher than 30?J/cm2.     

Cognitive ability experiment with photosensitive organic molecular thin films

We present an optical experiment which permits us to evaluate the information exchange necessary to self-induce cooperatively a well-organized pattern in a randomly activated molecular assembly. A low-power coherent beam carrying polarization and wavelength information is used to organize a surface relief grating on a photochromic polymer thin film which is photoactivated by a powerful incoherent beam. We demonstrate experimentally that less than 1% of the molecules possessing information cooperatively transmit it to the entire photoactivated polymer film.     

White organic light-emitting devices

In view of their potential applications in flat panel displays, organic light-emitting devices have attracted much attention in the past decade. A challenging target in this field is to realize full color display applications. One of the approaches proposed for these is combining white emission with color filters, where efficient and pure white emission (especially at high brightness) is necessary. In this paper, three kinds of white organic light-emitting devices with different structures and materials are fabricated and their characteristics are discussed.     

High-external-quantum-efficiency organic light-emitting devices

We study the internal and external quantum efficiencies of vacuum-deposited organic light-emitting devices (OLED's). The internal quantum efficiency of OLED's based on tris-(8-hydroxyquinoline) aluminum is calculated to be 5.7 times the observed external quantum efficiency ?(e), consistent with measurements. We demonstrate a shaped substrate that increases ?(e) by a factor of 1.9+/-0.2 over similar OLED's fabricated upon flat glass substrates and leads to a 100%-emissive aperture, i.e., the emitting area completely occupies the display area even in the presence of metal interconnects. We also discuss a substrate structure that increases ?(e) by an additional factor of 2. The high device efficiencies are promising for developing OLED-based displays with extremely low power consumption and increased operational lifetime.     

A simple encapsulation method for organic optoelectronic devices

The performances of organic optoelectronic devices, such as organic light emitting diodes and polymer solar cells,have rapidly improved in the past decade. The stability of an organic optoelectronic device has become a key problem for further development. In this paper, we report one simple encapsulation method for organic optoelectronic devices with a parafilm, based on ternary polymer solar cells(PSCs). The power conversion efficiencies(PCE) of PSCs with and without encapsulation decrease from 2.93% to 2.17% and from 2.87% to 1.16% after 168-hours of degradation under an ambient environment, respectively. The stability of PSCs could be enhanced by encapsulation with a parafilm. The encapsulation method is a competitive choice for organic optoelectronic devices, owing to its low cost and compatibility with flexible devices.     

Spatial light manipulation devices using nonlinear polymeric materials

An electrically addressed spatial light modulator with 5 × 5 pixels is designed using nonlinear polymeric materials. Resonator structure for the material is proposed to minimize the driving voltages. Side-chain polymer poly-orange tom-1 isophoronedisocyanate (r ₃₃ = 23 pm/V) is used as a material. A modulation efficiency of 4.7% has been realized with 5.1 V_rms applied voltage at a wavelength of 633 nm. Very fast modulation at over 10 MHz has been demonstrated.     

High-contrast top-emitting organic light-emitting devices

In this paper we report on a high-contrast top-emitting organic light-emitting device utilizing a moderate-reflection contrast-enhancement stack and a high refractive index anti-reflection layer.The contrast-enhancement stack consists of a thin metal anode layer,a dielectric bilayer,and a thick metal underlayer.The resulting device,with the optimized contrast-enhancement stack thicknesses of Ni(30 nm)/MgF 2(62 nm)/ZnS(16 nm)/Ni(20 nm) and the 25-nm-thick ZnS anti-reflection layer,achieves a luminous reflectance of 4.01% in the visible region and a maximum current efficiency of 0.99 cd/A(at 62.3 mA/cm 2) together with a very stable chromaticity.The contrast ratio reaches 561:1 at an on-state brightness of 1000 cd/m 2 under an ambient illumination of 140 lx.In addition,the anti-reflection layer can also enhance the transmissivity of the cathode and improve light out-coupling by the effective restraint of microcavity effects.     

Surface modified polymeric gate insulators for pentacene organic thin-film transistors

This paper demonstrates effects of a surface modification of polymeric gate insulators on a performance of organic thin-film transistor (OTFT). Pentacene OTFTs were fabricated with three types of polymer gate insulators—poly(4-vinylphenol) (PVP, G1) with comparably high dielectric constant, polyimide (PI, G2) with n-octadecyl (C₁₈) side chain, which resulted in hydrophobicity and low dielectric constant, and surface modified PVP(G3). The G3 was prepared by a spin-coating the solution of G2 onto the G1 film. We found that the n-octadecyl group of the G3 protruded from the surface and made the PVP surface more hydrophobic. The less polar surface strongly improved the device performance. Subthreshold slope (s.s.) of the OTFT with G3 as the gate insulator decreased significantly to 2.7 V/dec, which was much smaller than that of OTFTs fabricated with G1 (4.0 V/dec). That is, thin layer with fewer C₁₈ group in contact with pentacene induced a good electrical property like lower s.s. Further the higher dielectric constant of the underlying layer resulted in higher mobility of the device. The mobility (0.50 cm² V⁻¹ s⁻¹) of the OTFT with G3 as the gate insulator showed a higher value compared to that (0.25 cm² V⁻¹ s⁻¹) of the OTFT with G2.     

Isophorone derivative as red dopant for organic electroluminescent devices

The donor–acceptor functionalized molecule, bis(4-(2-(3,3-dicyanomethylene-5,5-dimethyl-1-cyclohexylidene)vinyl)phenyl)(1-naphthyl)amine (DPN-4CN), with symmetrical structure, was investigated for its application in optoelectronic devices. Red organic light-emitting diodes (OLEDs) were fabricated by doping DPN-4CN in tris(8-hydroxyquinolino) aluminum (Alq₃) as red emitters, with a structure of ITO/NPB/Alq₃:DPN-4CN/BCP/Alq₃/LiF/Al. The device with a doping concentration of 2.5 wt% showed pure red emission with λ_max at 654 nm and CIE coordinates of (0.62, 0.36), a high brightness of 5080 cd m⁻² at a driving voltage of 12 V, a current efficiency of 2.14 cd A⁻¹ and an external quantum efficiency of 1.07% at a current density of 20 mA cm⁻². The current efficiencies and CIE coordinates of the device were almost constant over a current density from 1 to 200 mA cm⁻².     

有机发光器件的磁电导效应

制备了基于三(8-羟基喹啉)铝(tris-(8-hydroxyquinoline) aluminum (III), Alq₃) 的有机发光二极管, 并在不同偏压下测量了器件的室温磁电导效应.在小偏压下, 发光器件展示出明显的负磁电导效应.偏压增加后, 磁电导由负值变为正值, 出现了正负转变的现象. N, N'-二苯基-N, N'-(1-萘基)-1, 1'-联苯-4, 4'-二胺(N, N′-Di(naphthalen-1-yl)-N, N′ diphenyl-benzidine, NPB) 与铜酞菁 (Copper phthalocyanine, CuPc) 单极器件磁电导的测量结果表明, 发光器件在小偏压下的负磁电导效应来源于器件中的CuPc层. 双极电流的磁电导效应可用电子-空穴对模型进行解释, 而单极电流的磁电导效应可归因于器件中的极化子-双极化子转变. 在注入电流的变化过程中, 发光器件的正负磁电导转变是两种机理共同作用的结果.     

Optimization of F-doped SnO2 electrodes for organic photovoltaic devices

Fluorine-doped tin oxide (FTO) thin films have been investigated as an alternative to indium tin oxide anodes in organic photovoltaic devices. The structural, electrical, and optical properties of the FTO films grown by pulsed laser deposition were studied as a function of oxygen deposition pressure. For 400 nm thick FTO films deposited at 300°C and 6.7 Pa of oxygen, an electrical resistivity of 5×10⁻⁴ Ω-cm, sheet resistance of 12.5 Ω/□, average transmittance of 87% in the visible range, and optical band gap of 4.25 eV were obtained. Organic photovoltaic (OPV) cells based on poly(3-hexylthiophene)/[6,6]-phenyl-C₆₁-butyric acid methyl ester bulk heterojunctions were prepared on FTO/glass electrodes and the device performance was investigated as a function of FTO film thickness. OPV cells fabricated on the optimum FTO anodes (∼300–600 nm thick) exhibited power conversion efficiencies of ∼3%, which is comparable to the same device made on commercial ITO/glass electrodes (3.4%).