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1.
Thin films of N,N′-bis-(3-Naphthyl)-N,N′-biphenyl-(1,1′-biphenyl)-4,4′-diamine (NPB), tris-(8-hydroxyquinoline)-aluminum (Alq3) and their blends prepared by spin-coating process were investigated. Experimental results revealed that the NPB films prepared by spin-coating process have smoother surface than that of Alq3, which was attributed to their different molecular structures. Organic light-emitting devices (OLEDs) with emitting layer prepared by spin-coating the blends of NPB and Alq3 exhibited a maximum luminance and a current efficiency over 10,000 cd/m2 and 3.8 cd/A respectively, and when 10-(2-benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H,11H-[l]benzopyrano[6,7,8-ij]quinolizin-11-one was doped in, a current efficiency of 8 cd/A can be obtained. Comparative device performance to the vapor-deposited OLEDs suggested that solution-process could be an alternative route for the fabrication of OLEDs based on Alq3. 相似文献
2.
M.S. Kim 《Thin solid films》2006,515(3):891-895
Three-wavelength white organic light-emitting diodes (WOLEDs) were fabricated using two doped layers, which were obtained by separating the recombination zones into three emitter layers. A sky blue emission originated from the 4,4′-bis(2,2′-diphenylethen-1-yl)biphenyl (DPVBi) layer. A green emission originated from a tris(8-quinolinolato)aluminum (III) (Alq3) host doped with a green fluorescent 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-[1]benzopyrano [6,7,8-ij]-quinolizin-11-one (C545T) dye. An orange emission was obtained from the N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) host doped with a red fluorescent dye, 4-(dicyanomethylene)-2-tert-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB). A white light resulted from the partial excitations of these three emitter layers by controlling the layer thickness and concentration of the fluorescent dyes in each emissive layer simultaneously. The electroluminescent spectrum of the device was not sensitive to the driving voltage of the device. The white light device showed a maximum luminance of approximately 53,000 cd/m2. The external quantum and power efficiency at a luminance of approximately 100 cd/m2 were 2.62% and 3.04 lm/W, respectively. 相似文献
3.
Improved performances in a top-emitting green organic light-emitting device with light magnification
A top-emitting organic light-emitting device (TOLED) with an architecture of Si/SiO2/Ag (100 nm)/Ag2O (UV ozone treatment for 30 s)/ 4′,4?-tris(3-methylphenylphenylamino)triphenylamine (45 nm)/4,4′-bis [N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl (5 nm)/tris-(8-hydroxyquinoline) aluminum (Alq3):10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo[l]-pyrano[6,7,8-ij]quinolizin-11-one (C545T) (1: 0.5 weight %, 20 nm)/Alq3 (30 nm)/LiF(1 nm)/Al (0.5 nm)/Ag(30 nm) is designed with a resonance wavelength in the TOLED corresponding to the peak wavelength of C545T. With this enhanced cavity structure, light magnification with a coefficient of ∼ 19 (forward direction) is observed, leading to significantly improved performances with brightness of 80215 cd/m2 at 9 V, luminous efficiency of 32.7 cd/A at 6 V, external quantum efficiency of 8.9% at 7.5 V, and low turn-on voltage of 2.5 V. 相似文献
4.
Organic light-emitting diodes (OLEDs) were fabricated based on copper phthalocyanine (CuPc) (hole-injecting layer), N,N′-bis(1-naphthyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB) (hole-transporting layer) and tris(8-hydroxyquinoline) aluminum (Alq3) (emission and electron-transporting layer). A 2-(4-biphenylyl)-5(4-tert-butyl-phenyl)-1,3,4-oxadiazole (PBD) layer was inserted between CuPc and NPB. The effect of different thickness of PBD layer on the performance of the devices was investigated. The device structure was ITO/CuPc/PBD/NPB/Alq3/LiF/Al. Optimized PBD thickness was about 1 nm and the electroluminescent (EL) efficiency of the device with 1 nm PBD layer was about 48 percent improvement compared to the device without PBD layer. The inserted PBD layer improved charge carriers balance in the active layer, which resulted in an improved EL efficiency. The performance of devices was also affected by varying the thickness of NPB due to microcavity effect and surface-plasmon loss. 相似文献
5.
The degradation behaviors of the electrical and the optical properties of organic light-emitting devices (OLEDs) fabricated with an emitting layer (EML) doped with or without a wide-bandgap-impurity were investigated. The OLEDs with a wide-bandgap-doped Alq3 EML were more stable than those with an undoped Alq3 EML. The existence of the doped wide-bandgap-impurity in the EML decreased the trap-charge density in the EML, resulting in an increase in the number of electrons in the Alq3 EML. That increases in the number of electron in the Alq3 EML for the OLEDs with a wide-bandgap-impurity decreased the staying time of the holes in the Alq3 EML, resulting in an enhanced lifetime for the OLEDs. These results indicate that OLEDs with a wide-bandgap-impurity-doped EML hold promise for potential applications in long-lifetime OLED displays. 相似文献
6.
The dipyridamole drug [DIP: 2,6-bis(diethanolamino)-4,8-dipiperidinopyrimido(5,4-d)pyrimidine] is widely used in treatment of coronary heart disease for its antiplatelet and vasodilating activities, and its high intensity photoluminescence (PL) has been widely reported. In this work, the fabrication and the characterization of a new OLED using the DIP molecule as an emitting layer is reported. The devices were assembled using a heterojunction between three organic molecular materials: the N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB) or the 1-(3-methylphenyl)-1,2,3,4-tetrahydroquinoline-6-carboxyaldehyde-1,1′-diphenylhydrazone (MTCD) as hole-transporting layer, the DIP layer as an emitting layer and the tris(8-hydroxyquinoline aluminum) (Alq3) as the electron transporting layer. All the organic layers were sequentially deposited in a high vacuum by thermal evaporation onto indium tin oxide substrates and without breaking vacuum. Continuous electroluminescence emission was obtained in all configurations upon varying the applied bias voltage from 4 to 30 V, the observed wide emission band was centered at 493 nm. The luminance of the devices was about 1500 (cd)/m2 with 4.5 cd/A of efficiency for the best device. The charge transport behavior in the OLED is also discussed as a function of different carrier injection levels. 相似文献
7.
Most of the Organic Light-Emitting Diodes (OLEDs) have a multilayered structure composed of functional organic layers sandwiched between two electrodes. Thin films of small molecules are generally deposited by thermal evaporation onto glass or other rigid or flexible substrates. The interface state between two organic layers in OLED device depends on the surface morphology of the layers and affects deeply the OLED performance. The morphology of organic thin films depends mostly on substrate temperature and deposition rate. Generally, the control of the substrate temperature allows improving the quality of the deposited films. For organic compounds substrate temperature cannot be increased too much due to their poor thermal stability. However, studies in inorganic thin films indicate that it is possible to modify the morphology of a film by using substrate vibration without increasing the substrate temperature. In this work, the effect of the resonance vibration of glass and silicon substrates during thermal deposition in high vacuum environment of tris(8-quinolinolate)aluminum(III) (Alq3) and N,N′-Bis(naphthalene-2-yl)-N,N′-bis(phenyl)-benzidine (β-NPB) organic thin films with different deposition rates was investigated. The vibration used was in the range of hundreds of Hz and the substrates were kept at room temperature during the process. The nucleation and subsequent growth of the organic films on the substrates have been studied by atomic force microscopy technique. For Alq3 and β-NPB films grown with 0.1 nm/s as deposition rate and using a frequency of 100 Hz with oscillation amplitude of some micrometers, the results indicate a reduction of cluster density and a roughness decreasing. Moreover, OLEDs fabricated with organic films deposited under these conditions improved their power efficiency, driven at 4 mA/cm2, passing from 0.11 lm/W to 0.24 lm/W with an increase in their luminance of about 352 cd/m2 corresponding to an increase of about 250% in the luminance with respect to the same OLEDs fabricated in the same way and with the same conditions without substrate vibration. 相似文献
8.
S. Ouro Djobo J. C. Bernède Napo Kossi 《Journal of Materials Science: Materials in Electronics》2004,15(9):579-582
Poly(N-vinycarbazole) (PVK)/tris(8-hydroxy)-quinoline-aluminum (Alq3) bilayer diodes were deposited by vacuum evaporation onto SnO2 coated glass substrates. After deposition of an aluminum upper electrode, the diodes were studied by current–voltage (I–V) and electroluminescence–voltage (EL–V) measurements. It is shown that the luminescence of the structures should be attributed to Alq3. However the presence of evaporated PVK allows us to decrease the barrier height at the interface SnO2/PVK because of the localized states induced in the PVK band gap during the evaporation which allows multistep tunneling effect. The optimum Alq3 thickness is shown to be about 75 nm. 相似文献
9.
We demonstrated efficient white electrophosphorescence with a heavily doped phosphorescent blue emitter and a triplet exciton blocking layer (TEBL) inserted between the hole transporting layer (HTL) and the emitting layer (EML). We fabricated white organic light-emitting diodes (WOLEDs) (devices A, B, C, and D) using a phosphorescent red emitter; bis(2-phenylquinolinato)-acetylacetonate iridium III (Ir(pq)2acac) doped in the host material; N,N′-dicarbazolyl-3,5-benzene (mCP) as the red EML and the phosphorescent blue emitter; bis(3,5-Difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium III (FIrpic) doped in the host material; p-bis(triphenylsilyly)benzene (UGH2) as the blue EML. The properties of device B, which demonstrate a maximum luminous efficiency and external quantum efficiency of 26.83 cd/A and 14.0%, respectively, were found to be superior to the other WOLED devices. It also showed white emission with CIEx,y coordinates of (x = 0.35, y = 0.35) at 8 V. Device D, which has a layer of P-type 4,4′,4″-tri(N-carbazolyl)triphenylamine (TCTA) material between the HTL and TEBL, was compared with device A to determine the 430 nm emission peak. 相似文献
10.
《Materials science & engineering. C, Materials for biological applications》2004,24(1-2):229-232
We studied the effect of a mixed host of Alq3 and rubrene on the energy transfer and charge trapping processes in organic light-emitting devices with a red fluorescent dopant of 4-(dicyanomethylene)-2-tert-butyl-6 (1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB). The temperature dependence of electroluminescence (EL) properties is compared for the device with DCJTB doped into the Alq3 only host and that with the Alq3:rubrene mixed host. The device with the Alq3:rubrene mixed host shows an efficient red emission from DCJTB, negligible EL emission from Alq3, and a lower EL drive voltage compared to the device with the Alq3 only host. Upon cooling the device temperature, the EL emission from rubrene increases but the emission from Alq3 is still weak, and the quantum efficiency (QE) is almost temperature-independent for the device with the Alq3:rubrene mixed host. On the contrary, the EL emission from Alq3 increases and the QE decreases for devices with the Alq3 only host at low temperature. The results indicate that recombination of injected electrons and holes occurs on rubrene and subsequent energy transfer to DCJTB dominates in the device with the Alq3:rubrene mixed host. 相似文献
11.
The photoluminescence properties of one europium complex Eu(TFNB)3Phen (TFNB = 4,4,4-trifluoro-1-(naphthyl)-1,3-butanedione, Phen = 1,10-phenanthroline) doped in a hole-transporting material CBP (4,4′-N,N′-dicarbazole-biphenyl) films were studied. A series of organic light-emitting devices (OLEDs) using Eu(TFNB)3Phen as the emitter were fabricated with a multilayer structure of indium tin oxide, 250 Ω/square)/TPD (N,N′-diphenyl-N,N′-bis(3-methyllphenyl)-(1,1′-biphenyl)-4,4′-diamine, 50 nm)/Eu(TFNB)3phen (x): CBP (4,4′-N,N′-dicarbazole-biphenyl, 45 nm)/BCP (2,9-dimethyl-4,7-diphenyl-l,10 phenanthroline, 20 nm)/AlQ (tris(8-hydroxy-quinoline) aluminium, 30 nm)/LiF (1 nm)/Al (100 nm), where x is the weight percentage of Eu(TFNB)3phen doped in the CBP matrix (1-6%). A red emission at 612 nm with a half bandwidth of 3 nm, characteristic of Eu(III) ion, was observed with all devices. The device with a 3% dopant concentration shows the maximum luminance up to 1169 cd/m2 (18 V) and the device with a 5% dopant concentration exhibits a current efficiency of 4.46 cd/A and power efficiency of 2.03 lm/W. The mechanism of the electroluminescence was also discussed. 相似文献
12.
Enhanced efficiency of red phosphorescent organic light-emitting devices is observed by using a bis[2-(2′-benzothienyl)pyridinato-N,C3′] iridium(acetylacetonato) doped 4,4′-N,N′-dicarbazole-biphenyl (CBP) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) mixed host emitting layer. The CBP:TPBI mixed host device shows a maximum external quantum efficiency of 9.1%, which is dramatically improved compared to that of the CBP (6.6%) and TPBI (5.4%) single host devices. Such a mixed host strategy can also be exploited in red phosphor dibenzo[f,h]quinoxaline iridium (acetylacetonate) doped devices. Investigations reveal that the position of charge carrier recombination zone of the mixed host devices predominantly locates in the electron blocking layer/emitting layer interface. The efficiency enhancement is attributed to the optimized hole and electron injection balance and hence increased charge carrier recombination rate in the emitting layer. 相似文献
13.
Tianhang Zheng 《Thin solid films》2010,519(2):872-875
Organic light emitting device (OLED) with a fluorescence-interlayer-phosphorescence emissive structure (FIP EML) is proposed to solve efficiency roll-off issue effectively. By doping fluorescent emitter of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) and phosphorescent emitter of tris(1-phenylisoquinolinolato-C2,N)iridium(III) (Ir(piq)3) into the different regions of emission zone to form FIP EML in red OLED, an improvement of more than 20% in luminance efficiency roll-off compared with that of typical phosphorescent OLED with single EML in 10-500 mA/cm2 range has been obtained. Detailed mechanisms have been studied. Such improvement should be attributed to the distinct roles of the two emitters, where DCJTB mainly used to influence the carrier transport leading to an improved balance of charge carriers while Ir(piq)3 functions as the radiative decay sites for most generated excitons. Meanwhile, with the help of the formation of FIP EML, the redistribution of excitons in recombination zone, the suppression of non-radiative exciton quenching processes and the elimination of energy transfer loss also contribute to the enhancement of efficiency roll-off. The method proposed here may provide a route to develop efficient OLED for high luminance applications. 相似文献
14.
Young-Joo Lee Youngsuk Byun Je-Eun Kim Wonsuk Cha Jinwoo Kim 《Thin solid films》2007,515(14):5674-5677
We report the process of thermal degradation of organic light emitting devices (OLEDs) having multilayered structure of [LiF/tris-(8-hydroxyquinoline) aluminum(Alq3)/N,N′-Bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine (NPB)/copper phthalocyanine (CuPc)/indium tin oxide (ITO)/SiO2 on a glass] by synchrotron X-ray scattering. The results show that the thermally induced degradation process of OLED multilayers has undergone several evolutions due to thermal expansion of NPB, intermixing between NPB, Alq3, and LiF layers, dewetting of NPB on CuPc, and crystallization of NPB and Alq3 depending on the annealing temperature. The crystallization of NPB appears at 180 °C, much higher temperature than the glass transition temperature (Tg = 96 °C) of NPB. The results are also compared with the findings from the atomic force microscope (AFM) images. 相似文献
15.
We describe the design and synthesis of a sterically hindered yellow dopant, tetra(t-butyl)rubrene (TBRb) which, when doped in either 1,4-bis[N-(1-naphthyl)-N′-phenylamino]-biphenyl or aluminum tris(8-hydroxyquinoline) (Alq3) as emitter, shows nearly 25% increase in luminance efficiency over that of the state-of-the-art rubrene (Rb) device without significantly effecting its corresponding color. At 5% doping in Alq3 and 20 mA/cm2 current drive condition, the electroluminescence efficiency of TBRb reaches 8.5 cd/A and 2.8 lm/W with a yellow color of Commission Internationale de l'Eclairage chromaticity coordinates (CIEx,y) = [0.52, 0.48], which is among the best ever reported for yellow electrofluorescence in organic light-emitting devices. 相似文献
16.
Tianle Li Xiao Li Wenlian Li Bei Chu Zisheng Su Liangliang Han Zhizhi Hu 《Thin solid films》2009,517(16):4629-4632
A red-emitting rubrene derivative, 2-formyl-5,6,11,12-tetraphenylnaphthacene (2FRb) was separately doped into 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB) and tris-(8-hydroxyquinoline) aluminum (Alq3) as the emitting layer. The emission can be tuned from 580 nm to 607 nm in NPB host and 560 nm to 622 nm in Alq3 host. The Alq3-hosted devices show better performances: more saturated pure red emission peaking at 622 nm with CIEx,y = [x = 0.65, y = 0.35], a maximum luminance efficiency of 2.42 cd/A and a maximum luminance of 3100 cd/m2 by doping 3.2 wt.% 2FRb in Alq3 host. It indicates that the derivative of rubrene is a promising bipolar dopant for red light-emitting device. 相似文献
17.
Yunxiao FanJin Peng Shuo Wei Xiaoduan ChenYongliang Li Jun Lu 《Thin solid films》2011,519(22):7659-7663
Tris(8-hydroxyquinolate) aluminum(Alq3) thin films assembled with large-scaled nanorods have been fabricated on Al substrates through hydrothermal in-situ growth method assisted by the surfactant of sodium dodecylbenzenesulfonate. The obtained Alq3 thin film is composed of uniformly sized (500-800nm × 4-10 μm) nanorods with regular hexagonal cross section, which are assembled to form dense nanorod arrays perpendicularly to the Al substrate. X-ray diffraction revealed that the prepared Alq3 nanorods were the α-phase. Photoluminescence spectra showed that the Alq3 nanorods thin film possessed a spectral blue-shift (10 nm) compared with the Alq3 solution. The hydrothermal growth mechanism of nanorods was studied, which implied that the hydrothermal in-situ growth process on the metal substrate played an important role in the formation of the Alq3 nanorods thin film. This simple hydrothermal method provides a convenient fabrication approach for nanocrystalline functional organic/metal interface. 相似文献
18.
《Materials science & engineering. C, Materials for biological applications》2004,24(1-2):233-235
We report the fabrication and the characterization of white-organic-light-emitting devices consisting of a blue-emitting layer of 1,4-bis(2,2-diphenyl vinyl)benzene (DPVBi) and a red-emitting layer of 4-dicyanomethylene-2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-8-yl)vinyl]-4H-pyran (DCM2) doped into either 4,4′bis[N-(1-napthyl)-N-phenyl-amino]-biphenyl (α-NPD) or tris(8-hydroxyquinoline) aluminum (Alq3). The spectral emission depends on both the doping location of DCM2 and its doping concentration. The electroluminescence (EL) spectra consist of two broad bands around 460 nm (DPVBi) and 560 nm (α-NPD:DCM2) or 590 nm (Alq3:DCM2). We obtained an efficient white-light emission from the devices with the 0.2% DCM2 doping in α-NPD layer. The device shows the CIE coordinates of (0.33, 0.36), an external quantum efficiency (QE) of about 3.1%, and a luminous efficiency of 3.75 lm/W at luminance 100 cd/m2. The maximum luminance of about 41,000 cd/m2 was obtained. 相似文献
19.
Jae Wook Kwon 《Thin solid films》2010,518(22):6339-6342
The hole ohmic properties of the MoOx-doped NPB layer have been investigated by analyzing the current density-voltage properties of hole-only devices and by assigning the energy levels of ultraviolet photoemission spectra. The result showed that the performance of organic light-emitting diodes (OLEDs) is markedly improved by optimizing both the thickness and the doping concentration of a hole-injecting layer (HIL) of N, N′-diphenyl-N, N′-bis(1-naphthyl)-1,1′-biphenyl-4,4′-diamine (NPB) doped with molybdenum oxide (MoOx) which was inserted between indium tin oxide (ITO) and NPB. For the doping concentration of above 25%, the device composed of a glass/ITO/MoOx-doped NPB (100 nm)/Al structure showed the excellent hole ohmic property. The investigation of the valence band structure revealed that the p-type doping effects in the HTL layer and the hole concentration increased at the anode interfaces cause the hole-injecting barrier lowering. With both MoOx-doped NPB as a hole ohmic contact and C60/LiF as an electron ohmic contact, the device, which is composed of glass/ITO/MoOx-doped NPB (25%, 5 nm)/NPB (63 nm)/Alq3 (37 nm)/C60 (5 nm)/LiF (1 nm)/Al (100 nm), showed the luminance of about 58,300 cd/m2 at the low bias voltage of 7.2 V. 相似文献
20.
Phosphorescent organic light-emitting diodes (PHOLEDs) with an emitting layer of 4,4′-N,N′-dicarbazole-biphenyl codoped with phosphor fac-tri(phenylpyridine)iridium(III) [Ir(ppy)3] and fluorophore N,N’-dimethy-quinacridone (DMQA) are investigated. Predominant emission from DMQA due to the efficient energy transfer from Ir(ppy)3 to DMQA is observed. Such an energy transfer results in the transition of Ir(ppy)3 triplet to DMQA singlet, which reduces the Ir(ppy)3 exciton lifetime and hence suppresses the triplet-triplet annihilation and triplet-polaron annihilation of Ir(ppy)3 excitons, leading to dramatical reduction of the efficiency roll-off of the PHOLEDs. This transition of triplet to singlet strategy provides a method to improve the efficiency roll-off of the PHOLEDs. 相似文献