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A new method to increase the luminance and quantum efficiency of polymer light emitting diodes with a lower threshold voltage has been reported. The threshold voltage, luminance and quantum efficiency have been significantly improved by doping certain dopants with a lower highest occupied molecular orbital (HOMO) level into the hole transporting layer. A high performance device has been achieved by addition of the perylene and triphenylamine as a dopant into poly(N-vinylcarbazole). The luminance and quantum efficiency increase by 2-3 times in comparison with the undoped device, reaching 10000 cd/m2 in luminance and 0.58% in quantum efficiency, while threshold voltage is reduced to one half value. The energy diagram has been obtained by measuring the HOMO levels and band gap values. Based on this, the carriers injection and balance between electrons and holes as well as the action of dopant are discussed.

ZrO2/zircone nanolaminate thin films fabricated by atomic layer deposition were used for a distributed Bragg reflector (DBR) in green organic light-emitting diodes (OLEDs). It is found that the novel ZrO2/zircone DBR structure significantly improves the light purity of green OLEDs without interfering with intrinsic electroluminescence properties. The full width at half maximum (FWHM) of the EL spectral band for the green OLEDs decreases with respect to increasing the ZrO2/zircone pairs. The FWHMs of OLEDs with 0, 2, 4, and 6 pairs of ZrO2/zircone layers are 72 nm, 48 nm, 24 nm, and 12 nm, respectively. A super-narrow FWHM of 12 nm is achieved by using six pairs of the DBR structure. The EQE is increased from 10.7% to 16.1% with four pairs of ZrO2/zircone layers.

This work presents a strategy of nitrogen anion doping to suppress negative gate-bias illumination instability. The electrical performance and negative gate-bias illumination stability of the ZnSnON thin film transistors (TFTs) are investigated. Compared with ZnSnO-TFT, ZnSnON-TFT has a 53% decrease in the threshold voltage shift under negative bias illumination stress and electrical performance also progresses obviously. The stability improvement of ZnSnON-TFT is attributed to the reduction in ionized oxygen vacancy defects and the photodesorption of oxygen-related molecules. It suggests that anion doping can provide an effective solution to the adverse tradeoff between field effect mobility and negative bias illumination stability.

A new blue electroluminescent material, distyrylarylene(DSA) derivative, 4,4’-bis[2,2-(1-naphthyl, phenyl)vinyl]-1,1′-biphenyl(NPVBi) is designed and synthesized. The DSA derivative shows better thermal stability because of its high glass transition temperature. A blue organic light emitting diode(OLED) with the structure ITO/TPD/NPVBi/Alq/LiF/Al is studied. The electrolu-minescent(EL) spectrum of the OLED exhibits that light emission originates from NPVBi with a peak at 460 nm, its Commission Internationale de l’Eclairage(CIE) color coordinates are x=0.16, y=0.15, and showing independence of CIE color coordinates on current density. The new DSA derivative is expectable as a new candidate for blue light emitter in OLEDs.

Lung cancer is one of the most common malignancies in the world and one of the leading cancers that result in death. The aim of this study was to evaluate and compare the diagnostic value of the serum tumor marker pro-gastrin-releasing peptide 31-98 (ProGRP31-98) to pathological diagnosis as reference standard in patients with suspected small cell lung cancer (SCLC).Literature searches covering 1978 through to 2009 were performed in Pubmed, OVID, MEDLINE, EMbase, Cancerlit, China National Knowledge Infrastructure (CNKI), and CBM using the key search words; 'small cell lung cancer', 'tumor marker', 'ProGRP31-98' and 'diagnostic tests', 'ELISA', 'EIA' and 'diagnostic accuracy'. Studies were collected and data analyzed to evaluate the diagnostic value of serum ProGRP31-98 levels for the diagnosis of SCLC compared with pathology. Eligibility criteria for inclusion in the analysis were based on criteria for diagnostic research published by the Cochrane Screening and Diagnostic TestsGroup (SDTMG). The characteristics of the included articles were appraised and the data were extracted from the original articles for further statistical analysis of study heterogeneity using Review Manager 4.2 software. Based on study heterogeneity analysis, a suitable 'effect' model was selected to calculate pooled sensitivity and specificity by meta-analysis. A Summary Receiver Operating Characteristic (SROC) curve and the area under the curve (AUC) were generated and sensitivity analysis conducted.A total of 22 articles were entered into this meta-review, including 11 English articles with a quality at level C. In total, the studies involved 6759 subjects, of which 1470 were diagnosed with SCLC by pathology, and 5289 subjects diagnosed with non-SCLC (NSCLC). The meta-analysis showed that heterogeneity among studies was high (P = 0.00001, I(2) = 86.8%). With ELISA, the pooled sensitivity was 0.72 (0.70 to 0.75 at 95%CI) and the pooled specificity was 0.93 (0.92 to 0.94 at 95%CI); the SROC and the AUC were 0.8817. These data suggest that ProGRP31-98 has a relatively high rate of missed diagnosis (28%), but a relatively low rate of misdiagnosis (7%).From meta-analysis, we concluded that serum ProGRP31-98 is a valuable marker with a high specificity for diagnosis of SCLC with a similar diagnostic accuracy to pathology.

In order to establish a coculture system of ECs and SMCs and by which further study can be done.ECs in primary culture were grown on a side of Transwell membrane, and SMCs were grown on an other side of it or the bottom of culture well, so that two kinds of coculture systems were established, and detail observation on the coculture systems was carried out by transmission and scanning electron microscope.ECs in primary culture were positive of VI factor by immunocytochemistry staining. ECs and SMCs were grown well on both sides of Transwell membrane, relative to ECs monolayer of "cobblestone appearance", SMCs were multilayer of "hills and valleys appearance". ECs and SMCs on both sides of Transwell membrane could form the gap junctions by micropores.The coculture systems of ECs and SMCs were established successfully by modeling the structural relationship of vascular wall.

White organic light-emitting diode was realized by co-doping a blue dye p-di(p-N,N-diphenyl-amino-styryl)benzene(DSA-ph) and a red dye 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran(DCJTB) into a blue host 2-(t-butyl)-9,10-di(2-naphthyl)anthracene(TBADN), achieving a brightness of 11580 cd/m2 at 200 mA/cm2, and a maximum current efficiency of 7.53 cd/A. The improvement was due to efficiency energy transfer from host to guest by the aid of assistant energy transfer mechanism. The device introduced a (4,4'-N,N'-dicarbazole)biphenyl/4,4'-bis(N-carbazolyl)biphenyl(CBP) interlayer between separate double emissive layers with the same materials showed improved color stability, due to the blocking effect of the CBP layer, which contributed to stable and even exciton distribution in both blue and red emission layer.

The electroluminescence (EL) and photoluminescence (PL) characteristics of blue emitting ZnS: Tm3+ phosphors have been studied. The difference of the EL excitation mechanism from that of PL is also discussed. For EL excitation, the emission is concentrated more in the infra-red regions, whereas for PL excitation, blue emission dominates the spectrum. It is found that the PL excitation mechanism of Tm3+ centers is attributable to the non-radiative energy transfer from the ZnS host to the Tm3+ centers. In contrast with PL, the dominant EL excitation mechanism results from the direct impact excitation of the Tm3+ centers by hot electrons rather than energy transfer. The cause for the relative inefficiency of blue emission in EL is that the excitation of the lower lying 3F4 state is dominant compared with that of the higher lying 1G4 state.

Organic electroluminescent (EL) devices using tris(8-hydroxyquinoline)–gallium complex (Gaq3) as the emitting layer were developed. Results indicated that EL devices using Gaq3 as emitting layers emitted light at a peak wavelength of 540 nm. The maximum luminance of these devices was obviously higher than that of devices using Alq3 and Znq2 as emitting layers prepared with the same structures and under the same conditions as Gaq3. The greatest maximum luminance of Gaq3 devices was attributed to the higher breakdown voltage and quantum efficiency than those of the other two devices.

Degradation characteristics of sealed OLED devices under four different constant currents were investigated by using OLEDs aging tester. We found that the higher the applied current density was, the faster luminance decayed. There was a relationship between luminance and lifetime when the current density was within 200mA/cm2. In addition, spectrum characterization indicated that the peak wavelength didn't shift during the aging process, which implied that the carriers recombination occurred near the NPB/Alq 3 interface all along even when OLEDs luminance dropped down to half of the initial value, indicating that the degradation wouldn't lead to the deviation of the carriers recombination region. Through the metallurgical microscopy observation, the number of bubbles and dark spots were noticed to increase continuously and the non-emissive area kept growing around the bubbles. It showed that bubbles would badly accelerate the formation of dark spots. By investigating luminance degradation under constant current, we draw a conclusion that OLEDs luminance degradation is not entirely coulombic. After introducing an acceleration coefficient, the formular could be applicable until the current went beyond some degree.

In multilayer OLED devices, the order and thickness of the emission layers have great effect on their spectrum. Based on the three basic colours of red, blue and green, a series of white organic light-emitting diodes(WOLEDS)with the structure of ITO/CuPc(12 nm)/NPB(50 nm)/EML/LiF(1 nm)/Al(100 nm) and a variety of emission layer's orders and thicknesses were fabricated. The blue emission material: 2-t-butyl-9,10-di-(2-naphthyl)anthracene (TBADN) doped with p-bis(p-N, N-diphenyl-amono-styryl)benzene(DSA-Ph), the green emission material: tris-[8-hydroxyquinoline]aluminum(Alq3) doped with C545, and the red emission material: tris-[8-hydroxyquinoline]aluminum( Alq3) doped with 4-(dicyanomethylene)-2-t-butyl-6-(1, 1, 7, 7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) were used. By adjusting the order and thickness of each emission layer in the RBG structure, we got a white OLED with current efficiency of 5.60 cd x A(-1) and Commission Internationale De L'Eclairage (CIE) coordinates of (0. 34, 0.34) at 200 mA x cm(-2). Its maximum luminance reached 20 700 cd x m(-2) at current density of 400 mA x cm(-2). The results were analyzed on the basis of the theory of excitons' generation and diffusion. According to the theory, an equation was set up which relates EL spectra to the luminance efficiency, the thickness of each layer and the exciton diffusion length. In addition, in RBG structure with different thickness of red layer, the ratio of th e spectral intensity of red to that of blue was calculated. It was found that the experimental results are in agreement with the theoretical values.

The blue top-emitting organic light-emitting devices with cavity effect have been fabricated. The authors used the TBADN : 3% DSAPh as emitting material of blue microcavity OLEDs. The devices consisted of Ag/ITO/CuPc/NPB/TBADN : 3% DSAPh/Alq3/LiF/Al(Ag) structure. On a patterned glass substrate, silver was deposited as reflective anode, and copper phthalocyanine (CuPc) layer as HIL and 4'-bis[N-(1-Naphthyl)-N-phenyl-amino] biphenyl (NPB) layer as HTL were made. Aluminum and silver thin films were made as semi-transparent cathode. The transmittance of aluminum and silver (Al/Ag) cathode was about 30%. In EL spectrum, the full width at half maximum (FWHM) was only 17 nm. By changing the thicknesses of ITO, highly saturated color with Commission Internationale de L'Eclairage chromaticity coordinates (CIEx,y) of (0.141, 0.049) was obtained. In the present article, the emission intensity of spectrum was studied. An appropriate cathode transmittance will result in maximal emission intensity. By using the formula of microcavity, the approximative curve that describes the change of emission intensity with cathode transmittance (or reflectance) was figured out.

This study investigates the effect of hafnium doping on the density of states (DOSs) in HfZnSnO thin film transistors fabricated by dual-target magnetron co-sputtering system. The DOSs is extracted by temperature-dependent field-effect measurements, and they decrease from 1.1 × 1017 to 4.6 × 1016 eV/cm3 with increasing the hafnium concentrations. The behavior of DOSs for the increasing hafnium concentration HfZnSnO thin film transistors can be confirmed by both the reduction of ΔVT under bias stress and the trapping charges calculated by capacitance voltage measurements. It suggests that the reduction in DOSs due to the hafnium doping is closely related with the bias stability and thermal stability.

The genomic DNA of a carbofuran-degrading bacterium Sphingomonas sp. CDS-1 was digested by Sau3Al and ligated to pRobe-GFP digested by BamHI, and the product was transformed to the E. coli DH5alpha competent cells. Fifty positive clones that could emit green fluorescence under UV were selected from about 1 x 10(4) clones grown on selective plates AmpLB. One clone F7 with the strongest fluorescence was selected, the recombinant plasmid pF7 from this clone was digested with EcoR IHind III and the DNA fragment comprising gfp and promoter of Sphingomonas sp. CDS-1 was recovered, which was subsequently cloned into the broad host vector pPZP201 to construct a new plasmid pPZP201-gfp. pPZP201-gfp was introduced into Sphingomonas sp. strain CDS-1 by triparental conjugation to make strain CDS-gfp. gfp was expressed strongly and stably in strain CDS-gfp after 10 times successive re-culturing (48 h/time). The linA gene was inserted into Not I -cut transposon vector pUT/mini-Tn5 to construct a new transposon vector pUT/mini-Tn5-linA. With the aid of helper plasmid pRK600, pUT/mini-Tn5-linA was introduced into CDS-gfp, the dehydrochlorinase gene linA was integrated into the chromosome of CDS-gfp by transposing. The double labelled strain CDS-GFP-LinA was constructed. This strain was also a genetic engineering strain that was able to degrade gamma-hexachlorocyclohexane and carbofuran simultaneously. All of these results laid a foundation for the study of ecological performance of Sphingomonas sp. CDS-1.

This paper proposes an algorithm for extracting the fetal electrocardiogram (FECG), which exploits the time structure and high-order statistics of the FECG. To accelerate the convergence, a variable step-size strategy is adopted. Compared with the Barros's algorithm, the proposed algorithm can rapidly obtain clearer FECGs. The validity and performance of the algorithm is confirmed by computer simulations and experiments on real-world data

A organic electroluminescent device has been fabricated by using a mixed layer as an emitter. The configuration of the device is ITO/TPD/TPD: PBD(equimole)/PBD/A1, in which TPD (N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine) and PBD (2-(4'-biphenyl)-5-(4''-tert-butylphenyl)-1,3,4-oxadiazole) are used as hole transport material and electron transport material, respectively. Broad and red-shifted electroluminescent spectra related to the fluorescence of constituent materials were observed. It is suggested that the monomer, exciplex and electroplex emissions are simultaneously involved in EL spectra by comparison of the EL with the PL spectra and decomposition of the EL spectrum. The type of exciplex is the interaction between the excited state TPD (TPD*) and PBD in the ground state, and the type of electroplex is a (D+-A-)* complex by cross-recombination of hole on the charged hole transport molecule (D+) and electron on the charged electron transport molecule (A-). All types of excited states show different formation mechanisms and recombination processes under electric field. The change of emission strengths from monomer and excited complexes lead to a blue-shift of the emissive spectra with an increasing electric field. The maximum luminance and external quantum efficiency of this device are 240 cd x (cm2)(-1) and 0.49%, respectively. The emissions from exciplex or electroplex formation at the organic solid interface generally present a broad and red-shifted emissive band, providing an effective method for tuning of emission color in organic electroluminescent devices.

The blue organic light emitting diodes (OLED) based on anthracene derivatives (ADN) doped with distryrylarylene derivatives (BCzVB and DSA-ph) were presented. The device of ADN doped with BCzVb shows high color purity (x=0.146, y=0.162) with maximum luminance 11600 cd/m2 (15V), current efficiency 2.8 cd/A, while the device of ADN doped with DSA-ph exhibits a sky blue with as high as efficiency 8.29 cd/A, both have a flat efficiency vs current density responses. A typical blue device of ADN doped with TBPe is used for comparison, which gives greenish blue and a stronger current-induced flyorescence quenching. Three kinds of White organic light emitting devices (WOLED) with different dopants and doping sites were constructed. The cell with a single-doped red dye in the light emitting layer (EML)(single-doped) and the cell with both red and blue dyes doped in a single EML (double-doped as well as the cell with red and blue dyes doped in EML and a green dye in another layer (triple-doped). The triple-doped cell shows much higher performance than other two cells: maximum luminance 21200cd/m2, 1026 cd/m2 at driving current 20mA/cm2, efficiency 6cd/A and a half lifetime over 22245h were reached. A passive display features 102x64 pixels with pixel size of 0.25x0.25mm2 pixel pitch 0.08mm, luminance 100 cd/m2 at driving duty 1/64, and power consumption of 0.6W was constructed.

Two kinds of voltage-tunable-color triple layer organic light emitting diodes consisted of styryltriphenyamine SA and 8- hydroxyquinoline aluminum chalet Alq3 or laser dye DCM doped Alq3 as emission layers and oxadizole PBD as carrier confinement layer have been fabricated. They emit both from SA and Alq3 or DCM doped Alq3 and their emission color dependent on the applied voltage. The ratios of blue from SA and green or orange-red from Alq3 or Alq3:DCM increased with the increasing of applied voltage. Brightness current characteristic has been invest9iEnergy models have been assumed and the EL behaviors are explained.© (1998) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A bit-panel-plus-weight method has been proposed to realize gray-scale control of synchronous VGA display by passive matrix OLED. The presented VGA controller has been fabricated by FPGAs and can achieve a better result of gray-scale control by a 96*64 PMOLED panel.

Impedance (Z), phase (φ) and capacitance (C) versus bias voltage (V) characteristics are studied to clarify carrier injection and recombination characteristics in organic light-emitting diodes (OLEDs). The Z–V transition starts at a characteristic voltage (Vc), which is strongly frequency dependent, i.e. Vc shifts to a high voltage with increasing measuring frequency. The electron–hole recombination starts at a voltage above Vc revealed by the φ–V and C–V transitions, which correspond to a phase approaching 0, a sharp rise in current density and a decrease in capacitance. Hole injection starts at a low Vc and corresponds to charge carrier accumulation and a slight rise in capacitance. Cole–Cole impedance plots illustrate that the interfacial resistance corresponds to the impedance at ultrahigh frequencies and shows bias independence, while the impedance at low frequencies represents the sum of interfacial resistance and organic stacks, and exhibits considerable bias dependence.

This paper presents white organic light-emitting diodes (WOLEDs) based on a novel double-emitting layer consisting of blue and white emitters. A blue fluorescent host of 4,40-bis(2,2-diphenylvinyl)-1,10-biphenyl (DPVBi) doped with 1,4-bis[2-(3-N-ethylcarbazoryl)vinyl]benzene (BCzVB) is used as the blue emitter, and this blue matrix doped with 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4 H-pyran (DCJTB) is used as the white emitter. In this double-emitting system, the blue emitter not only emits but also assists energy transfer from DPVBi to DCJTB. More significantly, this blue emitter is expected to act as an effective trapping site for holes. It leads to the efficient recombination of electron–hole pairs in the emission region. The white emitter is used to fabricate WOLEDs, in which DCJTB, tris-(8-hydroxyquinoline) aluminum (Alq3) and DPVBi contribute to the red, green and blue emissive components, respectively. We have observed that this strategy can greatly improve the device performances such as better chromaticity, improved color stability and enhanced efficiency. Through the optimization of the device structure, a balanced white emission with Commission Internationale de L'Eclairage (CIE) color coordinates of (0.33, 0.37) was obtained. This device showed stable color coordinates, i.e. the maximum color shift is less than 0.02 units on CIE color coordinates at the current density range of 4–200 mA cm−2. The maximum luminance achieved was 21 044 cd m−2 at a driving voltage of 17 V, and the maximum luminance efficiency reached was 9.12 cd A−1 at the luminance of 292 cd m−2. Such excellent performance shows that this double-emitting layer structure has great potential as a white light source for eventual applications.

We fabricated different SiNx insulators at a 150–350 °C deposition temperature by plasma-enhanced chemical vapor deposition (PECVD) and investigated the effect of SiNx insulator on the device properties of pentacene-TFTs with a low-cost copper source/drain electrode. A pentacene-TFT with a SiNx insulator at a deposition temperature of 300 °C exhibited the highest saturation mobility of 0.29 cm2 (V s)−1, the lowest threshold voltage of −8.9 V and an on/off current ratio of 5.3 × 106. The best performance of the device with a SiNx insulator at a 300 °C deposition temperature can be attributed to the electrical properties and a relatively large water contact angle of insulator, smooth insulator surface and better crystallinity of the pentacene active layer. The present organic thin-film transistors (OTFTs) with the PECVD SiNx insulator and the low-cost Cu electrode could be a significant step toward the commercialization of OTFT technology.

Pentacene-based organic thin film transistors (OTFTs) with WO3/Au as source/drain (S/D) electrodes were fabricated. In comparison with the pentacene-based OTFT having Au-only S/D electrodes, the performance of a device having WO3/Au S/D electrodes has been considerably improved. The saturation mobility increased from 0.39 to 2.8 cm2 (V s)?1, the threshold voltage reduced from ?21.3 to ?11.2 V, the on/off ratio shifted from 6.7 ? 105 to 1.5 ? 107 and the threshold swing varied from 3.75 to 1.82 V dec?1. The improvement was attributed to (i) the significant reduction of contact resistance by using the WO3 interlayer and (ii) the strong heat radiation during the thermal evaporation of WO3. Our results indicated that using WO3/Au as S/D electrodes is an effective approach to improving pentacene-based OTFT's performance.

p-di(p-N,N-diphenyl-amino-styryl)benzene (DSA-Ph)-based blue top-emitting organic light-emitting devices (TOLEDs) with low bias and single-mode resonant emission were fabricated. Microcavity optimization was demonstrated by altering the hole-transport-layer thickness. C60 was demonstrated to be an effective capping layer and improved the luminance by a factor of 1.6 in between the maximum and minimum transmittance of top contact. For sky-blue TOLED, the luminance was enhanced by 50% by using a dual emission layer composed of DSA-Ph doped 2-(t-butyl)-9,10-di(2-naphthyl)anthracene and DSA-Ph doped tris(8-hydroquinoline) aluminium (Alq3). The improvement was attributed to the energy transfer from Alq3 to DSA-Ph and DSA-Ph directly harvesting carriers in the emission layer of Alq3 : DSA-Ph.

A dual electron-transport layer (d-ETL) with hole-blocking function was successfully applied to a 2-(t-butyl)-9,10-di(2-naphthyl)anthracene (TBADN)-based blue organic light-emitting device (OLED) for improving chromaticity and electron injection. The d-ETL was constructed by sandwiching a 1,3-bis[2-(2,2'-bipyridin-6-yl)-1,3,4-oxadiazol-5-yl]benzene (Bpy-OXD) layer between the emission layer (EML) and the most common ETLs of tris(8-hydroquinoline) aluminum (Alq3) and 4,7-diphyenyl-1,10-phenanthroline (BPhen). Due to the hole-blocking function of Bpy-OXD and thereby the better confinement of carriers within the EML, d-ETL devices showed much better chromaticity and less current-induced color shift as compared to the corresponding single ETL ones. Moreover, the d-ETL devices revealed higher power efficiency (increased by ~30%) and lower driving voltage, indicating an enhanced electron injection. This could be explained by the fact that an interlayer of Bpy-OXD provided a stepped energy level which greatly facilitated electron injection and hence enhanced injection current.

We demonstrate highly efficient Alq3-based p–i–n organic light-emitting diodes by using cesium carbonate (Cs2CO3)-doped 4'7-diphyenyl-1, 10-phenanthroline (Bphen) as an electron transport layer, and by using molybdenum trioxide (MoO3)-doped N, N'-diphenyl-N, N'-bis(1,1'-biphenyl)-4,4'-diamine (NPB) as a hole transport layer, which could significantly enhance the electron injection and transport, resulting in a large increase in luminance and efficiency. The maximum luminance, current efficiency and power efficiency reach 23 420 cd cm−2, 6.4 cd A−1 and 5.3 lm W−1, respectively, which are much higher than those of the referenced device (without doping). This improvement is attributed to the improved conductivity of the transport layers and the efficient charge balance in the emission zone.

Organic light-emitting devices (OLEDs) with cohosted emitter, which is composed of 9,10-di(2-naphthyl)anthracene (ADN) and tris(8-hydroxy-quinolinato) aluminum (Alq3) and doped with 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethy ljulolidin-4-yl-vinyl)-4H-pyran (DCJTB), were fabricated and studied. The efficiency of OLEDs with a cohost emitter was higher than that with a single host emitter. For the cohost emitter with ADN/Alq3 weight ratio of 75:25, the 3.4 cd/A efficiency of the resulted OLEDs was obtained. It is found that the absorption spectra of DCJTB and the emission spectra of Alq3 changed with the composition of the emitter. This phenomenon is attributed to the polarization effect. On the basis of the Forster’s theory, the resulted overlap integral exhibits the highest value for this cohost emitter. The experimental results reveal that the cascade energy transfer plays an important role in the luminance efficiency enhancement of the cohost emitter in OLEDs.

Electron injection and transport in organic devices based on electron transport (ET) materials, such as 4,7- diphyenyl-1,10-phenanthroline (Bathophenanthroline BPhen), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (Bathocuproine BCP) and bipyridyl oxadiazole compound 1,3-bis [2-(2,2'-bipyridin-6-yl)-1,3,4-oxadiazol-5-yl]benzene (Bpy-OXD), have been reported. The devices are composed of ITO/ET materials (BPhen, BCP Bpy-OXD)/cathodes, where cathodes = Au, Al and Ca. Current–voltage characteristics of each ET material are performed as a function of cathodes. We have found that Ca and Al exhibit quite different J–V characteristics compared with the gold (Au) cathode. The current is more than one order of magnitude higher for the Al cathode and more than three orders of magnitude higher for Ca compared with that of the Au cathode at ~8 V for all ET materials. This is because of the relatively low energy barrier at the organic/metal interface for Ca and Al cathodes. Electron-only devices with the Au cathode show that the electron transfer limitation is located at the organic/cathode interface and the Fowler–Nordheim mechanism is qualitatively consistent with experimental data at high voltages. With Ca and Al cathodes, electron conduction is preponderant and is bulk limited. A power law dependence J ~ Vm with m > 2 is consistent with the model of trap-charge limited conduction. The total electron trap density is estimated to be ~5 × 1018 cm−3. The critical voltage (Vc) is found to be ~45 V and is almost independent of the materials.

We have demonstrated devices based on a p-doped layer consisting of 4,4',4''-tris(3-methylphenylphenylamono) triphenylamine (m-MTDATA) and tetrafluro-tetracyano-quinodimethane (F4-TCNQ) as a hole transport layer (HTL). The typical device structure is ITO/m-MTDATA: x% F4-TCNQ (40 nm)/N, N'-bis-[1-naphthy(-N, N' diphenyl-1,1'-biphenyl-4,4'-diamine)] (NPB) (10 nm)/tris (8-hydroxyquinoline) aluminum (Alq3) (50 nm)/LiF (10 nm)/Al (100 nm). Hole-only devices, where the current only consists of holes, are fabricated to observe the apparent improvement in the conductivity of the p-doped layers. We have observed that such layers lead to a striking improvement of the electrical properties of organic light-emitting devices. In particular, the electroluminescent onset voltage is observed to decrease continuously with increasing doping ratio and is greatly reduced compared to diodes with undoped layers. We have seen that the driving voltage of device 3 (m-MTDATA:4% F4-TCNQ) is reduced ~56% as compared with that of the control device (undoped). This improvement has been attributed to the increased conductivity of the p-doping hole transport layer. It is found that the current efficiency also decreases with increasing doping ratio. This can be attributed to the charge imbalance in the emission layer due to the excess hole injection.

We demonstrated efficient red organic light-emitting diodes based on a host emitting system of 9,10-di(2-naphthyl)anthracene (ADN) co-doped with 4-(dicyano-methylene)-2-t-butyle-6- (1,1,7,7-tetramethyl-julolidyl-9-enyl)-4H-pyran (DCJTB) as a red dopant and 2,3,6,7- tetrahydro-1,1,7,7-tetramethyl-1H,5H,1 1H-10(2-benzothiazolyl)-quinolizine-[9,9a,1gh] coumarin (C545T) as an assistant dopant. The typical device structure was glass substrate/ITO/4,4',4''-tris(N-3-methylphenyl-N-phenylamino) triphenylamine(m-MTDATA)/N,N'-bis-(naphthalene-1-yl)-N,N'-diphenylbenzidine(NPB)/[ADN: DCJTB: C545T/Alq3/LiF/Al]. It was found that C545T dopant did not emit by itself but did assist the energy transfer from the host (ADN) to the red emitting dopant. The red OLEDs realized by this approach not only enhanced the emission color, but also significantly improved the EL efficiency. The EL efficiency reached 3.5 cd A−1 at a current density of 20 mA cm−2, which is enhanced by three times compared with devices where the emissive layer is composed of the DCJTB doped ADN. The saturated red emission was obtained with CIE coordinates (x = 0.618, y = 0.373) at 621 nm, and the device driving voltage is decreased as much as 38%. We attribute these improvements to the assistant dopant (C545T), which leads to the more efficient energy transfer from ADN to DCJTB. These results indicate that the co-doped system is a promising method for obtaining high-efficiency red OLEDs.

Efficient top-emitting organic light-emitting devices (TOLEDs) using a thin MoOx layer modified Ag as the effective hole-injection anode are demonstrated. With tris-(8-hydroxy quinoline)aluminum as emitting layer and trilayer LiF∕Al∕Ag as semitransparent cathode, the Ag∕MoOx based TOLED shows a tune-on voltage of 2.67V and a maximum current efficiency of 7.27cd∕A, which are much better than those (3.92V, 6.12cd∕A) obtained from Ag∕Ag2O based TOLED and those (5.25V, 3.5cd∕A) obtained from the corresponding bottom-emitting organic light-emitting devices. Contact potential difference measurement shows that the work function of Ag∕MoOx is higher than those of Ag∕Ag2O and ozone-treated indium tin oxide, leading to a stronger hole injection. The good performance of Ag∕MoOx based TOLED is attributed to the efficient hole injection from the Ag∕MoOx anode as well as a microcavity effect.

The stability of organic electroluminescent devices is significantly improved by inserting a buffer layer between ITO and the holetransporting layer or by doping rubrene in the hole layer. The durabilities of the improved devices increase by a factor of about 10. The reasons for the improvements are discussed based on tunnelling theory and the energy-level diagram of the device.