Highly efficient two component phosphorescent organic light-emitting diodes based on direct hole injection into dopant and gradient doping

A series of two component phosphorescent organic light-emitting diodes (PHOLEDs) combing the direct hole injection into dopant strategy with a gradient doping profile were demonstrated. The dopant, host, as well as molybdenum oxide (MoO₃)-modified indium tin oxide (ITO) anode were investigated. It is found that the devices ITO/MoO₃ (0 or 1 nm)/fac-tris(2-phenylpyridine)iridium [Ir(ppy)₃]:1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) (30 → 0 wt%, 105 nm)/LiF (1 nm)/Al (100 nm) show maximum external quantum efficiency (EQE) over 20%, which are comparable to multi-layered PHOLEDs. Moreover, the systematic variation of the host from TPBi to 4,7-diphenyl-1,10-phenanthroline (Bphen), dopant from Ir(ppy)₃ to bis(2-phenylpyridine)(acetylacetonate)iridium [Ir(ppy)₂(acac)], and anodes between ITO and ITO/MoO₃ indicates that balancing the charge as well as controlling the charge recombination zone play critical roles in the design of highly efficient two component PHOLEDs.     

Green and blue-green phosphorescent heteroleptic iridium complexes containing carbazole-functionalized β-diketonate for non-doped organic light-emitting diodes

Two novel iridium complexes both containing carbazole-functionalized β-diketonate, Ir(ppy)₂(CBDK) [bis(2-phenylpyridinato-N,C²)iridium(1-(carbazol-9-yl)-5,5-dimethylhexane-2,4-diketonate)], Ir(dfppy)₂(CBDK) [bis(2-(2,4-difluorophenyl)pyridinato-N,C²)iridium(1-(carbazol-9-yl)-5,5-dimethylhexane-2,4-diketonate)] and two reported complexes, Ir(ppy)₂(acac) (acac = acetylacetonate), Ir(dfppy)₂(acac) were synthesized and characterized. The electrophosphorescent properties of non-doped device using the four complexes as emitter, respectively, with a configuration of ITO/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-diphenyl-4,4′-diamine (NPB) (20 nm)/iridium complex (20 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) (5 nm)/tris(8-hydroxyquinoline)aluminum (AlQ) (45 nm)/Mg_0.9Ag_0.1 (200 nm)/Ag (80 nm) were examined. In addition, a most simplest device, ITO/Ir(ppy)₂(CBDK) (80 nm)/Mg_0.9Ag_0.1 (200 nm)/Ag (80 nm), and two double-layer devices with configurations of ITO/NPB (30 nm)/Ir(ppy)₂(CBDK) (30 nm)/Mg_0.9Ag_0.1 (200 nm)/Ag (80 nm) and ITO/Ir(ppy)₂(CBDK) (30 nm)/AlQ (30 nm)/Mg_0.9Ag_0.1 (200 nm)/Ag (80 nm) were also fabricated and examined. The results show that the non-doped four-layer device for Ir(ppy)₂(CBDK) achieves maximum lumen efficiency of 4.54 lm/W and which is far higher than that of Ir(ppy)₂(acac), 0.53 lm/W, the device for Ir(dfppy)₂(CBDK) achieves maximum lumen efficiency of 0.51 lm/W and which is also far higher than that of Ir(dfppy)₂(acac), 0.06 lm/W. The results of simple devices involved Ir(ppy)₂(CBDK) show that the designed complex not only has a good hole transporting ability, but also has a good electron transporting ability. The improved performance of Ir(ppy)₂(CBDK) and Ir(dfppy)₂(CBDK) can be attributed to that the bulky carbazole-functionalized β-diketonate was introduced, therefore the carrier transporting property was improved and the triplet–triplet annihilation was reduced.     

A rational molecular design on choosing suitable spacer for better host materials in highly efficient blue and white phosphorescent organic light-emitting diodes

A series of host materials, 3,3′-linked carbazole-based molecules have been designed with phenyl and biphenyl spacers. Their optical and electrical properties can be fine-tuning by the spacers. Their HOMO energy levels depend on HOMO distributions within the range of −5.64 to −5.96 eV. On the other hand, the three compounds have similar LUMO energy levels and triplet energies. Their thermal, photophysical, electrochemical and carrier mobilities properties were also systematically investigated. The relationship between the molecular structures and optoelectronic properties are discussed. A blue PHOLED device incorporating PBCz achieved a maximum external quantum efficiency, current efficiency, and power efficiency of 19.5%, 45.5 cd/A and 43.8 lm/W, respectively. Moreover a two-color, all-phosphor and single-emitting-layer WOLED hosted by PBCz was also achieved with a maximum external quantum efficiency, current efficiency and power efficiency of 24.6%, 76.3 cd/A and 69.4 lm/W respectively. Furthermore, we also utilized this versatile host for three-component RGB white PHOLEDs and show excellent performance. For example, combination of PBCz with FIrpic, Ir(ppy)₂(acac) and Ir(MDQ)₂(acac) in the active layer, the resulting WOLEDs showed three evenly separated peaks and gave a high efficiency of 49.2 cd/A. The efficient PHOLEDs demonstrated that the versatile host PBCz has great potential for applications in the solid-state lighting.     

Highly efficient bluish green phosphorescent organic light-emitting diodes based on heteroleptic iridium(III) complexes with phenylpyridine main skeleton

A new series of heteroleptic iridium(III) complexes, bis(2-phenylpyridinato-N,C2′)iridium (2-(2′,4′-difluorophenyl)-4-methylpyridine), (ppy)₂Ir(dfpmpy) and bis(2-(2′,4′-difluorophenyl)-4-methylpyridinato-N,C2′)iridium (2-phenylpyridine) (dfpmpy)₂Ir(ppy), have been synthesized by using phenylpyridine as a main skeleton for bluish green phosphorescent organic light-emitting diodes (PhOLEDs). The Ir(III) complexes showed high thermal stability and high photoluminescent (PL) quantum yields of 95% ± 4% simultaneously. As a result, the PhOLEDs with the heteroleptic Ir(III) complexes showed excellent performances approaching 100% internal quantum efficiency with a very high external quantum efficiency (EQE) of ∼27%, a low turn-on voltage of 2.4 V, high power efficiency of ∼85 lm/W, and very low efficiency roll-off up to 20,000 cd/m².     

Electrical and optical characteristics of phosphorescent organic light-emitting device with thin-codoped layer insertion

In this paper, we demonstrated the changes of electrical and optical characteristics of a phosphorescent organic light-emitting device (OLED) with tris(phenylpyridine)iridium Ir(ppy)₃ thin layer (4 nm) slightly codoped (1%) inside the emitting layer (EML) close to the cathode side. Such a thin layer helped for electron injection and transport from the electron transporting layer into the EML, which reduced the driving voltage (0.40 V at 100 mA/cm²). Electroluminescence (EL) spectral shift at different driving voltage was observed in our blue OLED with [(4,6-di-fluoropheny)-pyridinato-N,C^2′]picolinate (FIrpic) emitter, which came from the recombination zone shift. With the incorporation of thin-codoped Ir(ppy)₃, such EL spectral shift was almost undetectable (color coordinate shift (0.000, 0.001) from 100 to 10,000 cd/m²), due to the compensation of Ir(ppy)₃ emission at low driving voltage. Such a methodology can be applied to a white OLED which stabilized the EL spectrum and the color coordinates ((0.012, 0.002) from 100 to 10,000 cd/m²).     

Novel dibenzothiophene based host materials incorporating spirobifluorene for high-efficiency white phosphorescent organic light-emitting diodes

Two host materials, DBTSF2 and DBTSF4, were designed and synthesized, incorporating dibenzothiophene (DBT) and spirobifluorene (SF) blocks. Their thermal, electrochemical and photo-physical properties were fully characterized. DBTSF4, which adopted an ortho-linkage between DBT and SF moieties, showed a significantly higher T₁ energy of 2.82 eV as compared to its para-linkage analogue DBTSF2 (2.49 eV). Their applications as host for green, blue and white phosphorescent organic light-emitting diodes (PHOLEDs) were explored. The DBTSF4 based blue PHOLED has a highest current efficiency of 23.5 cd A^?1. And using DBTSF4 as a single host, two-color based white PHOLEDs were achieved from cold white emission with CIE coordinate of (0.31, 0.43) to yellowish warm white emission (0.44, 0.49) with maximum current efficiencies varying from 35.8 to 52.3 cd A^?1 and maximum external quantum efficiencies from 13.1% to 16.9% respectively. The white PHOLED devices also showed a low efficiency roll-off even at 10,000 cd m^?2.     

Functionalized terfluorene for solution-processed high efficiency blue fluorescence OLED and electrophosphorescent devices

A new multifunctional blue-emitting terfluorene derivative (TFDPA) featured with triphenylamine groups for hole-transportation and long alkyl chains for solution processability on the conjugation inert bridge centers was reported. TFDPA can give homogeneous thin film by solution process and exhibits high hole mobility (μ_h ≈ 10^?3 cm² V^?1 s^?1) and suitable HOMO for hole injection. Particularly, TFDPA performs efficient deep-blue emission with high quantum yield (～100% in solution, 43% in thin film) and suitable triplet energy (E_T = 2.28 eV), making solution-processed OLED devices of using TFDPA as blue emitter and as host for iridium-containing phosphorescent dopants feasible. The solution-processed nondoped blue OLED device gives saturated deep-blue electroluminescence [CIE = (0.17, 0.07)] with EQE of 2.7%. TFDPA-hosted electrophosphorescent devices performed with EQE of 6.5% for yellow [(Bt)₂Ir(acac)], 9.3% of orange [Ir(2–phq)₃], and 6.9% of red [(Mpq)₂Ir(acac)], respectively. In addition, with careful control on the doping concentration of [(Bt)₂Ir(acac)], a solution-processed fluorescence–phosphorescence hybrided two-color-based WOLED with EQE of 3.6% and CIE coordinate of (0.38, 0.33) was successfully achieved.     

Enhancing the efficiency of simplified red phosphorescent organic light emitting diodes by exciton harvesting

High efficiency red phosphorescent organic light emitting diode (PHOLED) employing co-doped green emitting molecule bis(2-phenylpyridine)(acetylacetonate)iridium(III) [Ir(ppy)₂(acac)] and red emitting molecule bis(2-methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(III) [Ir(MDQ)₂(acac)] into 4,4′-bis(carbazol-9-yl)biphenyl (CBP) host in a simplified wide-bandgap platform is demonstrated. The green molecule is shown to function as an exciton harvester that traps carriers to form excitons that are then efficiently transferred to the Ir(MDQ)₂(acac) by triplet-to-triplet Dexter energy transfer, thereby significantly enhancing red emission. In particular, a maximum current efficiency of 37.0 cd/A and external quantum efficiency (EQE) of 24.8% have been achieved without additional out-coupling enhancements. Moreover, a low efficiency roll-off with the EQE remaining as high as 20.8% at a high luminance of 5000 cd/m² is observed.     

Ideal host and guest system in phosphorescent OLEDs

Ideal host-guest system for emission in phosphorescent OLEDs with only 1% guest doping condition for efficient energy transfer have been demonstrated in the present investigation. Using a narrow band-gap fluorescent host material, bis(10-hydroxybenzo[h] quinolinato)beryllium complex (Bebq₂), and red dopant bis(2-phenylquinoline)(acetylacetonate)iridium (Ir(phq)₂acac), highly efficient red phosphorescent OLEDs (PHOLEDs) exhibiting excellent energy transfer characteristics with a doping concentration of 1% were developed. Fabricated PHOLEDs show a driving voltage of 3.7 V, maximum current and power efficiencies of 26.53 cd/A and 29.58 lm/W, and a maximum external quantum efficiency of 21%. Minimized electron or hole trapping at the phosphorescent guest molecules and efficient Förster and Dexter energy transfers from the Bebq₂ host singlet and triplet states to the emitting triplet of Ir(phq)₂acac guest appear to be the key mechanism for ideal phosphorescence emission.     

Effect of electron injection and transport materials on efficiency of deep-blue phosphorescent organic light-emitting devices

We investigate the performance of FIr6-based deep-blue phosphorescent organic light-emitting devices (PHOLEDs) with three different electron transport materials, bathocuproine (BCP), 4,7-diphenyl-1,10-phenanthroline (BPhen), and tris[3-(3-pyridyl)mesityl]borane (3TPYMB), and study the effect of doping alkaline metals (Li and Cs) into these charge transport materials. External quantum efficiency (η_EQE) of (20 ± 1)% and peak power efficiency (η_P) of (36 ± 2) lm/W were achieved maintaining Commission Internationale de L’Eclairage (CIE) coordinates of (x = 0.16, y = 0.28) in p-i-n dual-emissive-layer (D-EML) deep-blue PHOLEDs with 3TPYMB as the electron transport material and 3TPYMB:Cs as the electron injection layer. The high efficiencies are attributed to the high triplet energy of 3TPYMB as well as the increased conductivity of 3TPYMB:Cs.     

Synthesis of phenylcarbazole–thiophene-based structural isomers as unipolar host materials for blue PHOLEDs and their device performance

New high triplet-energy host materials, which are symmetrically or asymmetrically designed by using phenylcarbazole and thiophene moieties, were synthesized by Suzuki–Miyaura cross-coupling reactions and their device performances of blue phosphorescent organic light-emitting diodes were also investigated. The synthesized compounds showed a high triplet energy (>2.84 eV) and good thermal stability. Highly efficient blue PHOLEDs were obtained when employing the symmetric compounds having C2 symmetry as the host material and bis[2-(4,6-difluorophenyl)pyridinato-C²,N](picolinato)iridium(III) (FIrpic) as the guest material. Their maximum external quantum efficiency of the device reached as high as 18.9% with blue color coordinate of (0.15, 0.35).     

Stable efficiency roll-off in blue phosphorescent organic light-emitting diodes by host layer engineering

The device characteristics of blue phosphorescent organic light-emitting diodes (PHOLEDs) with mixed host structure were investigated by changing the combination and the composition of host materials in emissive layer. The distributed recombination zone and balanced charge carrier injection within emissive layer were achieved through mixed host optimization with a hole transport-type and an electron transport-type host materials, therefore the device performances were greatly enhanced, with external quantum and power efficiencies of 21.8% and 53 lm/W. Moreover, mixed host blue PHOLEDs exhibited a extremely low stable efficiency roll-off with quantum efficiencies of 20.3% and 18.6% at a luminance of 1000 and 10,000 cd/m².     

High-performance azure blue quantum dot light-emitting diodes via doping PVK in emitting layer

Highly bright and efficient azure blue quantum dot-based light-emitting diodes (QD-LEDs) have been demonstrated by employing ZnCdSe core/multishell QDs as emitters and the crucial development we report here is the ability to dramatically enhance the efficiency and brightness through doping poly vinyl(N-carbazole) (PVK) in the emissive layer to balance the charge injection. The best device displays remarkable features like maximum luminance of 13,800 cd/m², luminous efficiency of 6.41 cd/A, and external quantum efficiency (EQE) of 8.76%, without detectable red-shift and broadening in electroluminescence (EL) spectra with increasing voltage as well as good spectral matching between photoluminescence (PL) and EL. Such azure blue quantum-dot LEDs show a 140% increase in external quantum efficiency compared with QD-LEDs without PVK. More important, the peak efficiency of the QD-LEDs with PVK dopant is achieved at luminance of about 1000 cd/m², and high efficiency (EQE > 8%) can be maintained with brightness ranging from 200 to 2400 cd/m². There are two main aspects of the role of PVK in the proposed system. Firstly, the lower HOMO of PVK than (poly[9,9-dioctylfluorene-co-N-[4-(3-methylpropyl)]-diphenylamine] (TFB) can reduce the potential barrier for 0.4 eV at the interface of QDs and hole transport layer which could result in higher hole injection efficiency along with good EQE as compared to TFB-only HTLs. Secondly, with PVK acting as buffer layer of TFB and QDs, the exciton energy transfer from the organic host to the QDs can be effectively improved.     

Hole mobilities of thermally polymerized triaryldiamine derivatives and their application as hole-transport materials in organic light-emitting diodes (OLEDs)

This paper describes the synthesis of three triaryldiamine derivatives presenting two thermally polymerizable trifluorovinyl ether groups that can be polymerized through thermal curing to form perfluorocyclobutyl (PFCB) polymers. These PFCB polymers, studied using time-of-flight techniques for the first time, exhibited remarkable non-dispersive hole-transport properties, with values of μ_h of ca. 10^?4 cm² V^?1 s^?1. When we employed these thermally polymerized polymers as hole-transport layers (HTLs) in electroluminescence devices containing tris(8-hydroxyquinolate) aluminum (Alq₃) as the emission layer, we obtained high current densities (ca. 3400 mA cm^?2), impressive brightnesses (5 × 10⁴ cd m^?2), and high external quantum efficiencies (EQEs = 1.43%). These devices exhibited the same turn-on voltage, but higher EQEs, relative to those incorporating the vacuum-processed model compound N,N′-di(1-naphthyl)-N,N′-diphenylbenzidine (α-NPD) (EQE = 1.37%) as the HTL under the same device structure.     

Charge conduction study of phosphorescent iridium compounds for organic light-emitting diodes application

The charge conduction properties of a series of iridium-based compounds for phosphorescent organic light-emitting diodes (OLEDs) have been investigated by thin-film transistor (TFT) technique. These compounds include four homoleptic compounds: Ir(ppy)₃, Ir(piq)₃, Ir(Tpa-py)₃, Ir(Cz-py)₃, and two heteroleptic compounds Ir(Cz-py)₂(acac) and FIrpic. Ir(ppy)₃, Ir(piq)₃ and FIrpic are commercially available compounds, while Ir(Tpa-py)₃, Ir(Cz-py)₃ and Ir(Cz-py)₂(acac) are specially designed to test their conductivities with respect to the commercial compounds. In neat films, with the exception of FIrpic, all Ir-compounds possess significant hole transporting capabilities, with hole mobilities in the range of about 5 × 10⁻⁶–2 × 10⁻⁵ cm² V⁻¹ s⁻¹. FIrpic, however, is non-conducting as revealed by TFT measurements. We further investigate how Ir-compounds modify carrier transport as dopants when they are doped into a phosphorescent host material CBP. The commercial compounds are chosen for the investigation. Small amounts of Ir(ppy)₃ and Ir(piq)₃ (<10%) behave as hole traps when they are doped into CBP. The hole conduction of the doped CBP films can be reduced by as much as 4 orders of magnitude. Percolating conduction of Ir-compounds occurs when the doping concentrations of the Ir-compounds exceed 10%, and the hole mobilities gradually increase as their values reach those of the neat Ir films. In contrast to Ir(ppy)₃ and Ir(piq)₃, FIrpic does not participate in hole conduction when it is doped into CBP. The hole mobility decreases monotonically as the concentration of FIrpic increases due to the increase of the average charge hopping distance in CBP.     

Synthesis,photoluminescence and electroluminescence properties of iridium complexes with bulky carbazole dendrons

We synthesized solution-processable iridium complexes having bulky carbazole dendrons, fac-tris[2-{3-(3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl)Phenyl)pyridine]iridium (III) (mCP)₃Ir and fac-bis[2-{3-(3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl)phenyl}pyridine][2-{3-(3,5-di(4-pyridyl)phenyl)phenyl}pyridine]iridium (III) (mCP)₂(bpp)Ir. Photoluminescence quantum efficiencies (PLQEs) of (mCP)₃Ir and (mCP)₂(bpp)Ir in their diluted solutions were 91% and 84%, respectively. They showed high PLQEs of 49% for (mCP)₃Ir and 29% for (mCP)₂(bpp)Ir even in a neat film. The triplet exciton energy level of the dendronized ligand (2.8 eV), 2-[3-{3,5-bis(3,6-di-n-butylcarbazol-9-yl)phenyl}]pyridine 10, and the dendron (2.9 eV), 3,5-bis(3,6-di-n-butylcarbazol-9-yl)benzene 7, are enough higher than that of the core complex Ir(ppy)₃ (2.6 eV). External quantum efficiency (EQE) of single layer light-emitting device with (mCP)₂(bpp)Ir was much higher than that of (mCP)₃Ir because of better affinity of (mCP)₂(bpp)Ir to cathode metal. When an electron transporting and hole-blocking material was used, the EQEs of double layer devices were dramatically improved to 8.3% for (mCP)₃Ir and 5.4% for (mCP)₂(bpp)Ir at 100 cd/m².     

High efficiency yellowish green phosphorescent emitter derived from phenylbenzothienopyridine ligand

A yellowish green phosphorescent dopant derived from phenylbenzothienopyridine ligand, iridium (III) [bis(1-phenylbenzo[4,5]thieno[2,3-c]pyridinato-N,C²]picolinate. (Ir(DTNP)₂pic) was synthesized and the device performances of the Ir(DTNP)₂pic was studied. The Ir(DTNP)₂pic dopant exhibited yellowish green emission at 548 nm and showed a high quantum efficiency of 22.4% at 1000 cd/m² with a color coordinate of (0.43, 0.57) in yellowish green phosphorescent organic light-emitting diodes.     

A highly efficient OLED based on terbium complexes

A neutral ligand 9-(4-tert-butylphenyl)-3,6-bis(diphenylphosphineoxide)-carbazole (DPPOC) and its complex Tb(PMIP)₃DPPOC (A, where PMIP stands for 1-phenyl-3-methyl-4-isobutyryl-5-pyrazolone) were synthesized. DPPOC has a suitable lowest triplet energy level (24,691 cm^?1) for the sensitization of Tb(III) (⁵D₄: 20,400 cm^?1) and a significantly higher thermal stability (glass transition temperature 137 °C) compared with the familiar ligand triphenylphosphine oxide (TPPO). Experiments revealed that the emission layer of the Tb(PMIP)₃DPPOC film could be prepared by vacuum co-deposition of the complex Tb(PMIP)₃(H₂O)₂ (B) and DPPOC (molar ratio = 1:1). The electroluminescent (EL) device ITO/N,N′-diphenyl-N,N′-bis(1-naphthyl)-1,1′-diphenyl-4,4′-diamine (NPB; 10 nm)/Tb(PMIP)₃ (20 nm)/co-deposited Tb(PMIP)₃DPPOC (30 nm)/2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP; 10 nm)/tris(8-hydroxyquinoline) (AlQ; 20 nm)/Mg_0.9Ag_0.1 (200 nm)/Ag (80 nm) exhibited pure emission from terbium ions, even at the highest current density. The highest efficiency obtained was 16.1 lm W^?1, 36.0 cd A^?1 at 6 V. At a practical brightness of 119 cd m^?2 (11 V) the efficiency remained above 4.5 lm W^?1, 15.7 cd A^?1. These values are a significant improvement over the previously reported Tb(PMIP)₃(TPPO)₂ (C).     

Poly(2-(N-carbazolyl)ethyl acrylate) as a host for high efficiency polymer light-emitting devices

Poly(2-(N-carbazolyl)ethyl acrylate), a poly(acrylate) comprised of carbazole-side groups attached via a flexible chain to the polymer backbone (PVAK) has been tested as host for solution-processed polymer light-emitting devices (PLEDs). This non-conjugated polymer proved to be an excellent candidate to host wide-bandgap phosphors. Notably, this polymer exhibited a high thermal stability (T_d = 322 °C), a glass transition temperature (T_g) of 91 °C and a wide bandgap corresponding to the pendent carbazole units and the disrupted π-conjugation of the polymer main chain, making this polymeric host a suitable candidate for wide bandgap triplet emitters. When tested as a host for FIrpic and Ir(ppy)₃, the resulting blue and green light-emitting devices showed a maximum luminous efficiency of 18.25 and 17.74 cd/A, respectively, which are comparable to recent reports of devices made using other carbazole-based oxygen-rich polymeric hosts. The polymer was also characterized by UV–visible absorption, photoluminescence spectroscopy as well as cyclic voltammetry.     

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.