Top-Emitting Organic Light-Emitting Devices Based on Silicon Substrate with High Luminance and Low Turn-on Voltage

We have fabricated a top-emitting organic light-emitting device on silicon substrate with high yellow luminance based on 5,6,11,12-tetraphenylnaphthacene sub-monolayer. It consists of a thin layer of highly conductive silver as the semitransparent cathode and surfaced-modified Ag as the anode. The device turns on at 3 V with the luminance of 8.4 cd/m^2. The maximum current efficiency is 1.3 cd/A at 6 V and the luminance reaches 14790 cd/m^2 at 14 V. The performance of the device is excellent in top-emitting organic light-emitting devices according to our knowledge.     

Enhanced Green Electrophosphorescence from Oxadiazole-Functionalized Iridium Complex-Doped Devices Using Poly（9,9-Dioctylfluorene） Instead of Poly（N-Vinylcarbazole） as a Host Matrix

Optoelectronic properties of the oxadiazole-functionalized iridium complex-doped polymer light-emitting devices （PLEDs） are demonstrated with two different polymeric host matrices at the dopant concentrations 1-8%. The devices using a blend of poly（9,9-dioctylttuorene）（PFO） and 2-（4-biphenyl）-5-（4-tert-butylphenyl）-1,3,4-oxadiazole （PBD） as a host matrix exhibited a maximum luminance efficiency of 11.3 cd/A at 17. 6 mA/cm^2. In contrast, the devices using a blend of poly（N-vinylcarbazole） （PVK） and PBD as a host matrix reveal only a peak luminance efficiency of 6.Scd/A at 4.1 mA/cm^2. The significantly enhanced electrophosphorescent emissions are observed in the devices with the PFO-PBD blend as a host matrix. This indicates that choice of polymers in the host matrices is crucial to achieve highly efficient phosphorescent dye-doped PLEDs.     

Highly Efficient Simplified Organic Light-Emitting Diodes Utilizing F4-TCNQ as an Anode Buffer Layer

We demonstrate that the electroluminescent performances of organic light-emitting diodes （OLEDs） are significantly improved by evaporating a thin F4-TCNQ film as an anode buffer layer on the ITO anode. The optimum Alq3-based OLEDs with F4-TCNQ buffer layer exhibit a lower turn-on voltage of 2.6 V, a higher brightness of 39820cd/m^2 at 13 V, and a higher current efficiency of 5.96cd/A at 6 V, which are obviously superior to those of the conventional device （turn-on voltage of 4.1 V, brightness of 18230cd/m^2 at 13 V, and maximum current efficiency of 2.74calla at 10 V）. Furthermore, the buffered devices with F4-TCNQ as the buffer layer could not only increase the efficiency but also simplify the fabrication process compared with the p-doped devices in which F4-TCNQ is doped into β-NPB as p-HTL （3.11 cd/A at 7 V）. The reason why the current efficiency of the p-doped devices is lower than that of the buffered devices is analyzed based on the concept of doping, the measurement of absorption and photoluminescence spectra of the organic materials, and the current density-voltage characteristics of the corresponding hole-only devices.     

Green-Yellow Electrophosphorescence from di [2,5-diphenyl- 1,3,4-oxadiazole C2′ , N^3] Platinum（Ⅱ） Doped PVK Devices

Employing a blend of poly (N-vinylcarbazole) (PVK) and 5-biphenyl-2-(4-tert-butyl)phenyl-1,3,4-oxadiazole) (PBD) as host matrix and a novel bicyclometalated Pt-complex containing 1,3,4-oxadiazole moiety as guest matrix with 2 wt. % doping concentration, we have demonstrated efficient phosphorescence-based polymer lightemitting devices (PLEDs). The devices emitted intense green yellow electrophosphorescence. No emission from either PVK or PBD was observed for the devices. The electroluminescence spectrum exhibited three primary peaks at 525nm, 568nm and 608nm. A maximum external quantum efficiency of 2.3% ph/el and a luminous efficiency of 3.Scd/A were achieved at a current density of 3.4mA/cm^2. The results demonstrate that highly efficient electrophosphorescence can be achieved from platinum complex-based polymer light-emitting devices.     

High—Efficiency Organic Double—Quantum—Well Light—Emitting Devices Using 5,6,11,12—Tetraphenylnaphthacene Sub—monolayer as Potential Well

The double-quantum-well organic light-emitting devices of indium-tin-oxide (ITO)/NPB (50nm)/rubrene (0.05nm)/NPB (4nm)/rubrene (0.05nm)/Alq3 (50nm)/LiF (0.5nm)/Al were fabricated, in which N,N-bis-(1-naphthyl)-N,N‘-diphenyl-1,1‘-biphenyl-4,4‘‘‘‘‘‘‘‘-diamine (NPB) is used as a barrier potential or hole transport layer, tris (8-hydroxyquinoline) aluminium (Alq3) used as electron transport layer, and 5,6,11,12-tetraphenylnaphthacene (rubrene) as a potential well and emitter. The brightness can reach 18610cd/m^2 at 13V. The maximum electroluminescent efficiency of the device was 6.61cd/A at 7V, which was higher than that of common dope-type devices. In addition, the electroluminescence efficiency is relatively independent of the drive voltage in the range from 5 to 13V.     

A New Kind of Buffer Layer of TiO2 Self—Assembled Material in Organic Electroluminescent Devices

A new kind of TiO2 self-assembled nanometre material has been fabricated and is used as a hole-injecting buffer layer in organic electroluminescent devices.The luminance and the efficiency of a devicy individually rises from 1500cd/m^2 to 5000cd/m^2 and from 2.0cd/.A to 3.92cd/A at the current density of 100mA/cm^2.The enhancements in brightness and efficiency are attributed to an improved balance of hole and electron injections due to blocking of the injected holes by the buffer layer and a more homogeneous adhesion of the hloe transprting layer to the anode.     

Improved Blue-Green Electrophosphorescence from a Tuning Iridium Complex with Benzyl Group in Polymer Light-Emitting Devices

Electroluminescence performances from a tuning biscyclometlated iridium complex with benzyl group are demonstrated in double-layered polymer light-emitting devices （PLEDs） using a blend of poly（9,9-dioctylfluorene） and 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole as a host matrix. Blue-green electrophosphorescent emission with a peak at 521 nm and a shoulder at 492nm was observed. The highest luminance efficiency of 4.8cd/A at current density of 0. 56 mA/cm^2 and a maximum luminance of 1944 cd/m^2 at 217.6 mA/cm^2 were achieved in the devices at the dopant concentration of 8%. The luminous performance of the devices becomes better with increasing dopant concentrations from 1% to 8%. This implies that the concentration quenching of this iridium complex with benzyl group can be efficiently inhibited in the devices.     

Nondoped Electrophosphorescent Organic Light-Emitting Diodes Based on Platinum Complexes

An undoped electrophosphorescent organic light-emitting diode is fabricated using a pure platinum（Ⅱ） （2-phenylpyridinato-N, Ca） （3-benzoyl-camphor） [（ppy）pt（bcam）] phosphorescent layer acting as the emitting layer. A maximum power efficiency Tlp of 6.621m/W and current efficiency of 14.78 cd/A at 745 cd/m2 are obtained from the device. The roll-off percentage of ηp of the pure phosphorescent phosphor layer device is reduced to 5% at a current density of 20mA/cm2, which is about 11% for conventional phosphorescent devices. The low roll-off efficiency is attributed to the phosphorescent material, which has the molecular structure of a strong steric hindrance effect.     

Enhancing The Efficiency of White Organic Light-emitting Diode Using Energy Recyclable Photovoltaic Cells

We demonstrate that power recycling is feasible by using a semi-transparent stripped Al electrode as interconnecting layer to merge a white organic light-emitting devices (WOLED) and an organic photovoltaic(OPV) cell. The device is called a PVOLED. It has a glass/ITO/CuPc/m-MTDATA∶V2O5/NPB/CBP∶FIrpic∶DCJTB/BPhen/LiF/Al/P3HT∶PCBM/V2O5/Al structure. The power recycling efficiency of 10.133% is achieved under the WOLED of PVOLED operated at 9 V and at a brightness of 2 110 cd/m2, when the conversion efficiency of OPV is 2.3%. We have found that the power recycling efficiency is decreased under high brightness and high applied voltage due to an increase input power of WOLED. High efficiency (18.3 cd/A) and high contrast ratio (9.3) were obtained at the device operated at 2 500 cd/m2 under an ambient illumination of 24 000 lx. Reasonable white light emission with Commission Internationale De L'Eclairage (CIE) color coordinates of (0.32,0.44) at 20 mA/cm2 and slight color shift occurred in spite of a high current density of 50 mA/cm2. The proposed PVOLED is highly promising for use in outdoors display applications.     

White organic light-emitting diodes based on a combined electromer and monomer emission in doubly-doped polymers

We report on white organic light-emitting diodes(WOLEDs) based on polyvinylcarbazole(PVK) doped with 1,1-bis((di-4-tolylamino)phenyl)cyclohexane(TAPC) and perylene,and investigate the luminescence mechanism of the devices.The chromaticity of light emission can be tuned by adjusting the concentration of the dopants.White light with the Commission Internationale de L’Eclairage(CIE) coordinates of(0.33,0.34) is achieved by mixing the yellow electromer emission of TAPC and the blue monomer emission of perylene from the device ITO/PVK:TAPC:perylene(100:9:1 in wt.)(100 nm)/tris-(8-hydroxyquinoline aluminum(Alq 3)(10 nm)/Al.The device exhibits a maximal luminance of 3727 cd/m2 and a current efficiency of 2cd/A.     

Highly Efficient Electrophosphorescence from a Grafted Biscyclometalated Iridium Complex with Triarylamine Unit in Polymer Light-Emitting Devices

The electroluminescence performance from a novel grafted cyclometalated iridium complex (BuPhNPPy)2Ir(acac)with triarylmine unit, where BuPhNPPy is N,N-di(4-tert-butylphenyl)-4-(2-pyridyl) phenylamine and Hacac is acetylacetone, is demonstrated in the double-layered polymer light-emitting devices (PLEDs). The PLEDs emit intense green phosphorescence at 533 nm with a shoulder peak of 566 nm employing 4 wt. % (BuPhNPPy)2Ir(acac)doped a blend of poly(vinylcarbazole) (PVK) and 2-tert-butylphenyl-5-biphenyl-l,3,4-oxadiazole (PBD) as the emitting layer. A maximum luminance of 14610cd/m^2 at voltage of 24 V and a maximum external quantum efficiency Eext of 10.4% photons per electron (ph/el) at current density of 32mA/cm^2 are achieved. When the current density is raised to 100mA/cm^2, Eext of the device still remained to 8.3% ph/el. This indicates that the triplet-triplet annihilation is restrained more effectively at high current density. The improvement of electrophosphorescence performances of the iridium complex may be contributed to an ortho-substituent effect of grafted triarylmine unit.     

White Organic Light-Emitting Devices Based on 2-（2-Hydroxyphenyl） Benzothiazole and Its Chelate Metal Complex

We present three kinds of organic light-emitting devices (OLED) fabricated to achieve the emission of bright and pure white light. Device A, with a double-layered structure using 2-(2-hydroxyphenyl) benzothiazole (HBT) and poly (N-vinylcarbazole) (PVK) as the emitting layer (EML) and the hole transport layer (HTL) respectively, could realize the blue-green light emission. Bis-(2-(2-hydroxyphenyl) benzothiazole)zinc (Zn(BTZ)2), synthesized with zinc acetate dihydrate and HBT to form a complex, is used as main EMLs in a similar structure to fabricate devices B and C. Bright and pure white light emissions can be obtained from device C which was fabricated with a green-white emitting host Zn(BTZ)2 and red dopant 5,6,11,12-tetraphenylnaphthacene (rubrene). The maximum quantum efficiency of device C could reach 0.63%, and the corresponding brightness and CIE coordinates were 4000cd/m^2 and (x=0.341, y=0.334) at the driving voltage of 20V.     

Improvement of Efficiency and Brightness of Red Organic Light－Emitting Devices Using Double－Quantum－Well Configuration

We present red double-quantum-well organic light-emitting devices (DQW-OLEDs), in which N,N-bis-(1-naphthyl)-N,N’-diphenyl-1,1‘-biphenyo-4,4‘-diamine (NPB) is used as potential barriers and hole transport layer, 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7, 7-thtramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) doped tris (8-hydroxyquinoline) aluminum (Alq3 ) as potential wells and emitter, undoped Alq3 as electron transport layer, respectively. The turn-on voltage is about 4 V. The maximum brightness and electroluminescent (EL) efficiency of the DQW device can reach 5916cd m^-2 at 16 V and 2.85cd A^-1 at 7 V, respectively. In addition, the EL efficiency of the DQW deviceis relatively independent of the drive voltage in the range from 5 V to 16 V.     

Efficiency of a blue organic light-emitting diode enhanced by inserting charge control layers into the emission region

We demonstrate high current efficiency of a blue fluorescent organic light-emitting diode (OLED) by using the charge control layers (CCLs) based on Alq3 . The CCLs that are inserted into the emitting layers (EMLs) could impede the hole injection and facilitate the electron transport, which can improve the carrier balance and further expand the exciton generation region. The maximal current efficiency of the optimal device is 5.89 cd/A at 1.81 mA/cm2 , which is about 2.19 times higher than that of the control device (CD) without the CCL, and the maximal luminance is 19.660 cd/m2 at 12V. The device shows a good color stability though the green light emitting material Alq3 is introduced as the CCL in the EML, but it has a poor lifetime due to the formation of cationic Alq3 species.     

High-efficiency organic light-emitting diodes based on ultrathin blue phosphorescent modification layer

Yellow organic light-emitting devices(YOLEDs) with a novel structure of ITO/MoO_3(5 nm)/NPB(40 nm)/TCTA(15 nm)/CBP:(tbt)_2Ir(acac)(x%)(25 nm)/FIrpic(y nm)/TPBi(35 nm)/Mg:Ag are fabricated. The ultrathin blue phosphorescent bis[(4,6-difluorophenyl)-pyridi-nato-N,C2■](picolinate) iridium(Ⅲ)(FIrpic) layer is regarded as a highperformance modification layer. By adjusting the thickness of FIrpic and the concentration of (tbt)_2Ir(acac), a YOLED achieves a high luminance of 41618 cd/m~2, power efficiency of 49.7 lm/W, current efficiency of 67.3 cd/A, external quantum efficiency(EQE) of 18%, and a low efficiency roll-off at high luminance. The results show that phosphorescent material of FIrpic plays a significant role in improving YOLED performance. The ultrathin FIrpic modification layer blocks excitons in EML. In the meantime, the high triplet energy of FIrpic(2.75 eV) alleviates the exciton energy transport from EML to FIrpic.     

Photovoltaic and Electroluminescence Bifunctional Devices with Starburst Amine and Rare-Earth-Complexes

We fabricate the organic photovoltaic （PV） devices, in which 4,4＇,4＂-tris-（2-methylphenylphenylamino）triphenylamine （m-MTDATA） and rare earth （RE） （dibenzoylmethanato）a（bathohenanthroline） （RE（DBM）abath） （RE = Nd or Pr） are used as electron donor and acceptor, and investigate their PV properties. The PV diode fabricated in the optimum processing conditions shows the open-circuit voltage of 1.91 V, short-circuit current of 0.1 mA/cm^2, fill factor of 0.38, and the overall power conversion efficiency of 1.9% when it is irradiated under UV light （4 m W/cm^2）. The photocurrent density exhibits an increase of 20% at least when a very thin LiF layer is inserted between the RE-complexes and the A1 cathode. A strong electroluminescence from the interface is also observed and the maximum luminance of a yellow emission resulted from the exciplex is 580 cd/m^2 at 17 V bias.     

Highly efficient blue organic light-emitting diodes using various hole and electron confinement layers

In this Letter, blue phosphorescence organic light-emitting diodes(PHOLEDs) employ structures for electron and/or hole confinement; 1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene is used as a hole confinement layer and tris-(phenylpyrazole)iridium [IreppzT3] is utilized for an electron confinement layer(ECL). The electrical and optical properties of the fabricated blue PHOLEDs with various carrier-confinement structures are analyzed.Structures with a large energy offset between the carrier confinement and emitting layers enhance the charge-carrier balance in the emitting region, resulting from the effective carrier confinement. The maximum external quantum efficiency of the blue PHOLEDs with the double-ECLs is 24.02% at 1500 cd∕m2and its luminous efficiency is 43.76 cd∕A, which is 70.47% improved compared to the device without a carrier-confinement layer.     

High Efficiency and Stable Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence Emitter

High efficiency,stable organic light-emitting diodes(OLEDs)based on 2-pheyl-4'-carbazole-9-H-Thioxanthen-9-one-10,10-dioxide(TXO-PhCz)with different doping concentration are constructed.The stability of the encapsulated devices are investigated in detail.The devices with the 10wt% doped TXO-PhCz emitter layer(EML)show the best performance with a current efficiency of 52.1 cd/A,a power efficiency of 32.7lm/W,and an external quantum efficiency(EQE)of 17.7%.The devices based on the 10wt%-doped TXO-PhCz EML show the best operational stability with a half-life time(LT50)of 80 h,which is 8h longer than that of the reference devices based on fac-tris(2-phenylpyridinato)iridium(Ⅲ)(fr(ppy)_3).These indicate excellent stability of TXO-PhCz for redox and oxidation processes under electrical excitation and TXO-PhCz can be potentially used as the emitters for OLEDs with high efficiency and excellent stability.The high-performance device based on TXO-PhCz with high stability can be further improved by the optimization of the encapsulation technology and the development of a new host for TXO-PhCz.     

White organic light-emitting diodes based on electroplex from polyvinyl carbazole and carbazole oligomers blends

White organic light-emitting diodes with a blue emitting material fluorene-centred ethylene-liked carbazole oligomer (Cz6F) doped into polyvinyl carbazole (PVK) as the single light-emitting layer are reported. The optical properties of Cz6F, PVK, and PVK:Cz6F blends are studied. Single and double layer devices are fabricated by using PVK: Cz6F blends, and the device with the configuration of indium tin oxide (ITO)/PVK:Cz6F/ tris(8-hydroxyquinolinate)aluminium (Alq₃)/LiF/Al exhibits white light emission with Commission Internationale de l'éclairage chromaticity coordinates of (0.30, 0.33) and a brightness of 402~cd/m². The investigation reveals that the white light is composed of a blue--green emission originating from the excimer of Cz6F molecules and a red emission from an electroplex from the PVK:Cz6F blend films.     

Highly Efficient Greenish-Yellow Phosphorescent Organic Light-Emitting Diodes Based on a Novel 2,3-Diphenylimidazo[1,2-a]Pyridine Iridium(Ⅲ) Complex

A cyclometalated greenish-yellow emitter 2,3-diphenylimidazo[1,2-a]pyridine iridium(Ⅲ) complex is successfully synthesized and used to fabricate phosphorescent organic light-emitting diodes.The optimized device exhibits a greenish-yellow emission with the peak at 523 nm and a strong shoulder at 557 nm,corresponding to Commission Internationale de l'Eclairage coordinates of(0.38,0.58).The full width at half maximum of the device is 93 nm,which is broader than the fac-tris(2-phenylpyridine)iridium[Ir(ppy)_3]based reference device of 78 nm.Meanwhile,a maximum current efficiency of 62.6 cd/A(47.51m/W) is obtained.This result is higher than a maximum current efficiency of 54.8 cd/A(431m/W) of the Ir(ppy)3 based device.The results indicate that this new iridium complex may have potential applications in fabricating high color rendering index white organic light emitting diodes.