Blue light-emitting OLED using new spiro[fluorene-7,9′-benzofluorene] host and dopant materials

A new spiro-type compound, 2-(10-biphenylanthracene)-spiro[fluorene-7,9′-benzofluorene] (BH-3B) containing anthracene moiety was prepared for the blue host material. Also new dopant materials, 2-[4′-(phenyl-4-vinylbenzeneamine)phenyl-spiro[fluorene-7,9′-benzofluorene] (BH-3BD) and 4-[2-naphthyl-4′(phenyl-4-vinylbenzeneamine)]phenyl (BD-1N) were successfully synthesized and a blue OLEDs were made from them. The structure of the device was as follows; ITO/DNTPD/α-NPD/Host:5% dopant/Alq₃/Al-LiF. Among all of the devices, the device obtained from BH-3B host doped with 5% BH-3BD showed the best electroluminescence characteristics. The emission peak of EL is at 456 nm and the CIE value is (0.15, 0.14). The brightness of the device is up to 5407 cd/m² at 10 V with the maximum EL efficiency of 3.4 cd/A.     

Efficient electron transport in 4,4′-bis[N-(1-napthyl)-N-phenyl-amino] biphenyl and the applications in white organic light emitting devices

The electron transport capability of 4,4′-bis[N-(1-napthyl)-N-phenyl-amino] biphenyl (α-NPD) was investigated by fundamental physical measurements named as current–voltage (I–V) electrical property evaluation and displacement current measurement (DCM). In electron-dominated devices, the I–V characteristics of α-NPD were similar as that of (8-hydroxyquinolino) aluminum (Alq₃) owing to their same order of electron mobilities. The interface of Al/LiF and α-NPD was proven to be an Ohmic contact through the evaluation of I–V characteristics at low bias regime (<3 V). And an electron injection barrier, 0.21 eV, at Al/LiF/α-NPD was obtained by extrapolating the temperature dependent I–V curves. The electron transport behavior in α-NPD film was further confirmed by DCM evaluations. Furthermore, an efficient white organic light emission device was successfully fabricated by using α-NPD as hole transport layer and electron transport layer, respectively.     

Improving the performance of blue phosphorescent organic light-emitting devices using a composite emitter

A composite emitter is constructed by doping a carrier-transporting material into a conventional emitter composing of only host and dopant. The transport of carriers from either hole- or electron-transporting layer into the emitter can be promoted through the carrier-transporting material, in particular, when a wide-band-gap host material is used. A blue phosphorescent OLED based on iridium(III)bis((4,6-difluorophenyl)-pyridinate-N,C^2′)-picolinate (FIrpic) as dopant in the composite emitter achieved a power efficiency of 20 lm/W and a low driving voltage of 4.2 V at 1000 cd/m², whose current efficiency at 20 mA/cm² was 2.5 times better than that of device using the conventional emitter.     

Efficient single layer RGB phosphorescent organic light-emitting diodes

We report efficient single layer red, green, and blue (RGB) phosphorescent organic light-emitting diodes (OLEDs) using a “direct hole injection into and transport on triplet dopant” strategy. In particular, red dopant tris(1-phenylisoquinoline)iridium [Ir(piq)₃], green dopant tris(2-phenylpyridine)iridium [Ir(ppy)₃], and blue dopant bis(3,5-difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl)iridium [FIrpic] were doped into an electron transporting 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) host, respectively, to fabricate RGB single layer devices with indium tin oxide (ITO) anode and LiF/Al cathode. It is found that the maximum current efficiencies of the devices are 3.7, 34.5, and 6.8 cd/A, respectively. Moreover, by inserting a pure dopant buffer layer between the ITO anode and the emission layer, the efficiencies are improved to 4.9, 43.3, and 9.8 cd/A, respectively. It is worth noting that the current efficiency of the green simplified device was as high as 34.6 cd/A, even when the luminance was increased to 1000 cd/m² at an extremely low applied voltage of only 4.3 V. A simple accelerated aging test on the green device also shows the lifetime decay of the simplified device is better than that of a traditional multilayered one.     

Molecular Engineering of Blue Fluorescent Molecules Based on Silicon End‐Capped Diphenylaminofluorene Derivatives for Efficient Organic Light‐Emitting Materials

Blue fluorescent materials based on silicone end‐capped 2‐diphenylaminofluorene derivatives are synthesized and characterized. These materials are doped into a 2‐methyl‐9,10‐di‐[2‐naphthyl]anthracene host as blue dopant materials in the emitting layer of organic light‐emitting diode devices bearing a structure of ITO/DNTPD (60 nm)/NPB (30 nm)/emitting layer (30 nm)/Alq₃ (20 nm)/LiF (1.0 nm)/Al (200 nm). All devices exhibit highly efficient blue electroluminescence with high external quantum efficiencies (3.47%–7.34% at 20 mA cm^?2). The best luminous efficiency of 11.2 cd A^?1 and highest quantum efficiency of 7.34% at 20 mA cm^?2 are obtained in a device with CIE coordinates (0.15, 0.25). A deep‐blue OLED with CIE coordinates (0.15, 0.14) exhibits a luminous efficiency of 3.70 cd A^?1 and quantum efficiency of 3.47% at 20 mA cm^?2.     

Blade coating of Tris(8-hydroxyquinolinato)aluminum as the electron-transport layer for all-solution blue fluorescent organic light-emitting diodes

Organic light-emitting diodes (OLEDs) with a low driving voltage and efficient blue fluorescence were fabricated through blade coating. Tris(8-hydroxyquinolinato)aluminum (Alq₃) is a relatively stable electron-transporting material commonly used in evaporation. However, depositing Alq₃ through a solution process is difficult because of its extremely low solubility organic solvents, a result of its symmetrical molecular structure. In this study, Alq₃ was successfully deposited through blade coating at a very low concentration below 0.1wt%. The OLEDs contained co-dopants BUBD-1 and p-bis(p-N,N-diphenyl-aminostyryl)benzene (DSA-Ph), and a high-band-gap host 2-methyl-9,10-bis(naphthalen-2-yl)anthracene (MADN) as the emission layer with the following structure: ITO/PEDOT:PSS (40 nm)/VB-FNPD (30 nm)/MADN:2% BUBD-1:1% DSA-Ph (50 nm)/TPBI (30 nm)/LiF (0.8 nm)/Al (100 nm)or ITO/PEDOT:PSS (40 nm)/VB-FNPD (30 nm)/MADN:3% BUBD-1 (50 nm)tris(8-hydroxyquinolinato)aluminum (Alq₃; 10 nm)/LiF (0.8 nm)/Al (100 nm). 2,7-disubstituted fluorene-based triaryldiamine(VB-FNPD)is the cross-linking transporting material. The device exhibited a peak current efficiency of 5.67 cd/A for Alq₃ and 5.76 cd/A for TPBI. The device with Alq₃ has operated lifetime seven times higher than the device with TPBI.     

Interfacial charges and electric field distribution in organic hetero-layer light-emitting devices

The electric field distribution in organic hetero-layer light-emitting devices based on N,N^′-diphenyl-N,N^′-bis(1-naphtyl)-1,1^′-biphenyl-4,4^′-diamine (NPB) and 8-tris-hydroxyquinoline aluminium (Alq₃) has been investigated under different bias conditions using capacitance–voltage measurements. Although this method yields primarily information on the differential capacitance, the data give clear evidence for the presence of negative interfacial charges with a density of 6.8×10¹¹e cm⁻² at the NPB/Alq₃ interface at large reverse bias. This leads to a jump of the electric field at the interface and a non-uniform field distribution in the hetero-layer device.     

Deep blue organic light-emitting diode using non anthracene-type fused-ring spiro[benzotetraphene-fluorene] with aromatic wings

We prepared three spirobenzotetraphene-based fused-ring spiro[benzo[ij]tetraphene-7,9′-fluorene] (SBTF) derivatives for use in non anthracene-type deep-blue organic light-emitting diode (OLED) hosts. 3-(2-Naphthyl)-10-naphthylspiro[benzo[ij]tetraphene-7,9′-fluorene] (N-NSBTF), 3-[4-(2-naphthyl)phenyl]-10-naphthylspiro[benzo[ij]tetraphene-7,9′-fluorene] (NP-NSBTF), and 3-(phenyl)-10-naphthylspiro[benzo[ij]tetraphene-7,9′-fluorene] (P-NSBTF) were synthesized via multi-step Suzuki coupling reactions. The optimized device structure – ITO/N,N′-bis-[4-(di-m-tolylamino)phenyl]-N,N′-diphenylbiphenyl-4,4′-diamine (DNTPD, 60 nm)/bis[N-(1-naphthyl)-N-phenyl]benzidine (NPB, 30 nm)/NSBTF hosts: LBD (5%) (20 nm)/aluminum tris(8-hydroxyquinoline) (Alq₃, 20 nm)/LiF/Al – was characterized by its blue electroluminescence to have a current efficiency of 6.25 cd/A, a power efficiency of 5.07 lm/W, and an external quantum efficiency of 5.24% at 18.7 mA/cm² at CIE coordinates of 0.130, 0.149.     

Optical performance of efficient blue/near UV nitropyridine-conjugated anthracene (NAMA) based light emitting diode

9-[(5-nitropyridin-2-aminoethyl) iminiomethyl]-anthracene (NAMA) was synthesized for the first time from the reaction between 9-antracene carboxaldehyde and 2-(2-aminoethylamino)-5-nitropyridine under mild reaction conditions. The structure of the nitropyridine-conjugated anthracene (NAMA) was characterized using ¹H-NMR, ¹³C-NMR and elemental analysis techniques. Furthermore, electroluminescent behavior of the NAMA was investigated by using a material based on polycyclic aromatic hydrocarbons (PAHs) in organic light-emitting diodes (OLEDs). It was observed that the NAMA exhibits blue/near UV emission at 410 nm with a high density signal. The optimized device structure, ITO/CuPc/α−NPD/NAMA/Alq₃/LiF/Al is characterized by blue/near UV electroluminescence (EL) and a high current density with 7735 cd m⁻² maximum brightness at approximately 10.4 V. The emitting color of the device showed the blue/near UV emission (x, y) = (0.14, 0.10) at 277.1 mA cm⁻² in CIE (Commission Internationale de l’Eclairage) chromaticity coordinates with a long operational lifetime (180 h).     

Comparison of two cohost systems for doped red organic light-emitting devices in an effort to improve the efficiency and the lifetime

Blue-emitting 2-methyl-9,10-di(2-napthyl)anthracene (MADN) and yellow-emitting 5,6,11,12-tetraphenylnaphthacene (rubrene) were used as cohost materials together with tris(8-hydroxyquinolinato)aluminum (Alq₃) to form emission layers doped with the red dopant molecule 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB). DCJTB-doped red organic light-emitting diodes based on both cohost systems showed remarkable improvements in terms of efficiency compared to DCJTB-doped Alq₃ single-host devices. With 2% DCJTB doping, the respective efficiencies of Alq₃ single-host, Alq₃ (60%)/rubrene (40%)-, and Alq₃ (20%)/MADN (80%)-cohost devices were 1.79, 4.44 and 5.42 cd/A at 20 mA/cm². Unlike Alq₃/rubrene-cohost devices, which experienced substantial current-induced quenching, Alq₃/MADN-cohost devices showed only a slight efficiency change at high current densities. At the luminance of 7680 cd/m², which was the benchmark for a practical passive-matrix OLED array with 64 scan-lines, an aperture ratio of 50%, and a polarizer transmittance of 50%, the power efficiency of the 2% DCJTB Alq₃/MADN-cohost device was 4.1 and 1.5 times better than that of Alq₃ single-host and Alq₃/rubrene-cohost devices, respectively. Moreover, the half-decay lifetime of the Alq₃/MADN-cohost device, measured as 14,000 h at an initial luminance of 1000 cd/m², was 4.4 and 1.9 times longer than the respective half-decay lifetimes of Alq₃ single-host and Alq₃/rubrene-cohost devices.     

White organic light-emitting diodes based on emission from DPVBi-doped 4,48-bis (2,28-diphenylvinyl)-1, 18-biphenyl

Organiclight-emitting diodes (OLEDs) have beenin-vestigated for many years on account of their highlumi-nance,low driven voltages ,wide visual range,flexiblesubstratesinflat-panel ,full color displays and backlightapplications .For high brightness and eff…     

MoO3 as p-type dopant for Alq3-based p–i–n homojunction organic light-emitting diodes

Using high-work-function material MoO₃ as a p-type dopant, efficient single-layer hybrid organic light-emitting diodes (OLEDs) with the p–i–n homojunction structure are investigated. When MoO₃ and Cs₂CO₃ are doped into the conventional emitting/electron-transport material tris-(8-hydroxyquinoline) aluminum (Alq₃), respectively, a significant increase in p- and n-type conductivities is observed compared to that of intrinsic Alq₃ thin films. With optimal doping, the hole and electron mobilities in Alq₃:MoO₃ and Alq₃:Cs₂CO₃ films was estimated to be 9.76 × 10⁻⁶ and 1.26 × 10⁻⁴ cm²/V s, respectively, which is about one order of magnitude higher than that of the undoped device. The p–i–n OLEDs outperform undoped (i–i–i) and single-dopant (p–i–i and i–i–n) OLEDs; they have the lowest turn-on voltage (4.3 V at 1 cd/m²), highest maximum luminance (5860 cd/m² at 11.4 V), and highest luminous efficiency (2.53 cd/A at 100 mA/cm²). These values are better than those for bilayer heterojunction OLEDs using the same emitting layer. The increase in conductivity can be attributed to the charge transfer process between the Alq₃ host and the dopant. Due to the change of carrier concentration in the Alq₃ films, the Fermi level of Alq₃ is close to the highest occupied molecular orbital (HOMO) or lowest unoccupied molecular orbital (LUMO) energy levels upon p- and n-type doping, respectively, and the carrier injection efficiency can thus be enhanced because of the lower carrier injection barrier. The carriers move closer to the center energy levels of the HOMO or LUMO distributions, which increases the hopping rate for charge transport and results in an increase of charge carrier mobility. The electrons are the majority charge carriers, and both the holes and electrons can be dramatically injected in high numbers and then efficiently recombined in the p–i–n OLEDs. As a result, the improved conductivity characteristics as well as the appropriate energy levels of the doped layers result in improved electroluminescent performance of the p–i–n homojunction OLEDs.     

To observe bidirectional negative differential resistance at room temperature by narrowing transport channels for charge carriers in vertical organic light-emitting transistor

Bidirectional negative differential resistance (NDR) at room temperature with high peak-to-valley current ratio (PVCR) of ～10 are observed from vertical organic light-emitting transistor indium-tin oxide (ITO)/N,N′-di(naphthalene-1-yl)-N,N′-diphenyl-benzidine) (α-NPD)(60 nm)/Al(30 nm)/α-NPD(60 nm)/tris-(8-hydroxyquinoline) aluminium (Alq₃)(50 nm)/Al by narrowing the transport channels for charge carriers with a thick-enough middle Al gate electrode layer to block charge carriers transporting from source electrode to drain electrode. When the transport channel for charge carriers gets large enough, the controllability of gate bias on the drain–source current gets weaker and the device almost works as an organic light-emitting diode only. Therefore, it provides a very simple way to produce NDR device with dominant bidirectional NDR and high PVCR (～10) at room temperature by narrowing transport channels for charge carriers in optoelectronics.     

Stable and efficient blue fluorescent organic light-emitting diode by blade coating with or without electron-transport layer

Multi-layer small-molecule blue fluorescent organic light-emitting diode (OLED) is fabricated by blade coating. The emission layer is based on a mixed host of 1-(7-(9,9′-bianthracen-10-yl)-9,9-dioctyl-9H-fluoren-2-yl)pyrene (PT-404) and electron-transport material 2,7-Bis(diphenylphosphoryl)-9,9′ -spirobifluorene (SPPO13), and the blue guest emitter is 4-4′-(1E,1′E)-2,2′-(naphthalene-2,6-diyl)bis(ethane-2,1-diyl)bis(N,N-bis(4-hexyl- Phenyl) aniline) (Blue D). A hole-transport layer of Poly-(9, 9-dioctylfluorenyl-2, 7-diyl)-co-(4, 4-(N-(4-sec-butylphenyl)) diphenylamine) (TFB) is added on top of PEDOT: PSS anode. The electrons are blocked away from TFB by a layer of pure host emission layer of PT-404 between TFB and the mixed –host emission layer. For the device with the electron transport layer of Tris(8-hydroxyquinolinato)aluminum (Alq₃) blade-coated over the emission layer the efficiency and lifetime at initial brightness of 500 cd m⁻² are 7.5 cd A⁻¹ and 150 h for Alq₃/CsF/Al cathode. When the Alq₃/CsF/Al is replaced by simply CsF/Al over the mixed-host emission layer the efficiency and lifetime are 6.4 cd A⁻¹ and 300 h (2 times longer than that of the Alq₃/CsF/Al cathode). The lifetime depends on the electron-hole balance tuned by the mixed-host blending ratio as well as the electron injection from the cathode. This work shows good stability is possible for all-solution-processed blue OLED.     

Dual enhancing properties of LiF with varying positions inside organic light-emitting devices

A multilayer organic light-emitting device (OLED) has been fabricated with a thin (0.3 nm) lithium fluoride (LiF) layer inserted inside an electron transport layer (ETL), aluminum tris(8-hydroxyquinoline) (Alq₃). The LiF electron injection layer (EIL) has not been used at an Al/Alq₃ interface in the device on purpose to observe properties of LiF. The electron injection-limited OLED with the LiF layer inside 50 nm Alq₃ at a one forth, a half or a three forth position assures two different enhancing properties of LiF. When the LiF layer is positioned closer to the Al cathode, the injection-limited OLED shows enhanced injection by Al interdiffusion. The Al interdiffusion at least up to 12.5 nm inside Alq₃ rules out the possible insulating buffer model in a small molecule bottom-emission (BE) OLED with a thin, less than one nanometer, electron injection layer (EIL). If the position is further away from the Al cathode, the Al diffusion reaches the LiF layer no longer and the device shows the electroluminescence (EL) enhancement without an enhanced injection. The suggested mechanism of LiF EL efficiency enhancer is that the thin LiF layer induces carrier trap sites and the trapped charges alters the distribution of the field inside the OLED and, consequently, gives a better recombination of the device. By substituting the Alq₃ ETL region with copper phthalocyanine (CuPc), all of the electron injection from the cathode of Al/CuPc interface, the induced recombination at the Alq₃ emitting layer (EML) by the LiF EL efficiency enhancer, and the operating voltage reduction from high conductive CuPc can be achieved. The enhanced property reaches 100 mA/cm² of current density and 1000 cd/m² of luminance at 5 V with its turn-on slightly larger than 2 V. The enhanced device is as good as our previously reported non-injection limited LiF EIL device [Yeonjin Yi, Seong Jun Kang, Kwanghee Cho, Jong Mo Koo, Kyul Han, Kyongjin Park, Myungkeun Noh, Chung Nam Whang, Kwangho Jeong, Appl. Phys. Lett. 86 (2005) 213502].     

Improved property in organic light-emitting diode utilizing two Al/Alq3 layers

We reported on the fabrication of organic light-emitting devices (OLEDs) utilizing the two Al/Alq₃ layers and two electrodes. This novel green device with structure of Al(110 nm)/tris(8-hydroxyquinoline) aluminum (Alq₃)(65 nm)/Al(110 nm)/Alq₃(50 nm)/N,N′-dipheny1-N, N′-bis-(3-methy1phyeny1)-1, 1′-bipheny1-4, 4′-diamine (TPD)(60 nm)/ITO(60 nm)/Glass. TPD were used as holes transporting layer (HTL), and Alq₃ was used as electron transporting layer (ETL), at the same time, Alq₃ was also used as emitting layer (EL), Al and ITO were used as cathode and anode, respectively. The results showed that the device containing the two Al/Alq₃ layers and two electrodes had a higher brightness and electroluminescent efficiency than the device without this layer. At current density of 14 mA/cm², the brightness of the device with the two Al/Alq₃ layers reach 3693 cd/m², which is higher than the 2537 cd/m² of the Al/Alq₃/TPD:Alq₃/ITO/Glass device and the 1504.0 cd/m² of the Al/Alq₃/TPD/ITO/Glass. Turn-on voltage of the device with two Al/Alq₃ layers was 7 V, which is lower than the others.     

Effect of type-II quantum well of m-MTDATA/α-NPD on the performance of green organic light-emitting diodes

The type-II multiple quantum well (MQW) structure is prepared and introduced into green organic green light-emitting diodes consisting of 4,4′-bis-[N-(naphthyl)-N-phenyl-amino]biphenyl (α-NPD) and tris-(8-hydroxyquinolinato)-aluminum (Alq₃). The quantum well (QW) and wall are fabricated by 4,4′,4″-tris-(3-methylphenylphenylamino)triphenylamine (m-MTDATA) and α-NPD, respectively. The device performance of MQW organic light-emitting diodes (OLEDs) has been improved; the luminous efficiency by 25% and power efficiency by 17% compared with the reference device. The performance improvement can be explained by the increased electron-hole balance in the device due to the hole confinement in the QW structure.     

Organic alternating current electroluminescence device based on 4,4′-bis(N-phenyl-1-naphthylamino) biphenyl/1,4,5,8,9,11-hexaazatriphenylene charge generation unit

An organic alternating current electroluminescence (OACEL) device based on 4,4′-bis(N-phenyl-1-naphthylamino) biphenyl (NPB)/1,4,5,8,9,11-hexaazatriphenylene (HAT-CN)/tris(8-hydroxy-quin-olinato) aluminum (Alq₃) doped with cesium carbonate (Cs₂CO₃) internal charge generation unit is demonstrated. Maximum luminance of 299 cd/m² is observed for Alq₃ doped with 10-(2-Benzothiazolyl)-2,3,6,7-tetrahydro-1,1,7,7-tetramethyl-1H,5H, 11H-(1) benzopyropyrano (6,7-8-I,j)quinolizin-11-one (C545T) fluorescent emission layer when driven with a peak–peak voltage of 80 V at 120 kHz. The key charge-generation role of NPB/HAT-CN interface is studied experimentally. Furthermore, influence of evaporation sequence of this internal charge generation unit on OACEL performance is investigated. This work demonstrated that the undoped charge generation unit – NPB/HATCN, can also be a good candidate for charge generation unit of OACEL device.     

Tuning electron injection/transporting properties of 9,10-diphenylanthracene based electron transporters via optimizing the number of peripheral pyridine for highly efficient fluorescent OLEDs

By incorporating different number of pyridine rings to the periphery of the 9,10-diphenylanthracene (DPA) core, four new pyridine-containing DPA derivatives, 3-(4-(10-phenylanthracen-9-yl)phenyl)pyridine (AnPy), 9,10-bis(4-(pyridin-3-yl)phenyl)anthracene (AnDPy), 3,3'-((2-(pyridin-3-yl)anthracene-9,10-diyl)bis(4,1-phenylene))dipyridine (AnTPy), 3,3'-(9,10-bis(4-(pyridin-3-yl)phenyl)anthracene-2,6-diyl)dipyridine (AnFPy) were designed and synthesized as electron transporters. Their photophysical properties, energy levels and electron mobilities can be readily regulated through tuning the quantity of the pyridine ring. Through optimizing electron injection/transporting properties, AnTPy exhibits not only a suitable lowest unoccupied molecular orbital (LUMO) energy level for electron injection into light-emitting layer (EML), but also a relatively high electron mobility of around 10⁻³ cm² V⁻¹ s⁻¹, which is about two orders of magnitude higher than that of the widely used material Alq₃. As expected, the blue fluorescent OLEDs with AnPy, AnTPy and AnFPy as an electron-transporting layer (ETL) exhibited superior performance compared to that using Alq₃, remarkably lowering the driving voltages and improving efficiencies. In particular, the device with AnTPy as an ETL showed a maximum current efficiency of 14.4 cd A⁻¹, a maximum power efficiency of 12.1 lm W⁻¹, a maximum external quantum efficiency (EQE) of 8.15% and low efficiency roll-off even at an illumination-relevant luminance of 10,000 cd m⁻². These results clearly demonstrated that tuning electron injection/transporting properties by optimizing the number of peripheral electron-withdrawing groups was an efficient strategy to achieve high-performance ETMs.     

New hole blocking material for green-emitting phosphorescent organic electroluminescent devices

The new amorphous molecular material, 2,5-bis(4-triphenylsilanyl-phenyl)-[1,3,4]oxadiazole, that functions as good hole blocker as well as electron transporting layer in the phosphorescent devices. The obtained material forms homogeneous and stable amorphous film. The new synthesized showed the reversible cathodic reduction for hole blocking material and the low reduction potential for electron transporting material in organic electroluminescent (EL) devices. The fabricated devices exhibited high performance with high current efficiency and power efficiency of 45 cd/A and 17.7 lm/W in 10 mA/cm², which is superior to the result of the device using BAlq (current efficiency: 31.5 cd/A and power efficiency: 13.5 lm/W in 10 mA/cm²) as well-known hole blocker. The ITO/DNTPD/α-NPD/6% Ir(ppy)₃ doped CBP/2,5-bis(4-triphenylsilanyl-phenyl)-[1,3,4]oxadiazole as both hole blocking and electron transporting layer/Al device showed efficiency of 45 cd/A and maximum brightness of 3000 cd/m² in 10 mA/cm².