Study on electrical characteristics of organic electrophosphorescent devices based on new Ir complex

Kim, Jun Ho; Nam, Eunwoo; Hong, Soo Yeon; Kim, Bong Ok; Kim, Sung Min; Yoon, Seung Soo; Suh, Jung Ha; Ha, Yunkyung; Kim, Young Kwan

doi:10.1016/j.msec.2003.09.005

Cited by 18 publications

(5 citation statements)

References 9 publications

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“…In a single BPhen ET layer, electrons hop along the LUMO in BPhen. The LUMO-LUMO difference between BPhen (3.0 eV) [26] and Liq (3.1 eV) [32] is very small. Therefore, transport is more likely to be expected along their LUMOs by electron hopping [24] among the BPhen and Liq sites.…”

Section: Resultsmentioning

confidence: 94%

“…A thin layer of 2,9-Dimethyl-4,7-diphenyl-1,10-phenanthroline (Bathocuproine BCP) is incorporated to impede holes to enter the ETL, since it possesses a highest occupied molecular orbital (HOMO) level (6.7 eV) [32]. The current density versus voltage characteristics of electron-only devices at various doping ratios of Liq to BPhen are shown in figure 3.…”

Section: Resultsmentioning

confidence: 99%

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Highly power efficient organic light-emitting diodes based on p-doped and novel n-doped carrier transport layers

Khan¹,

Xu²,

Khizar-ul-Haq³

et al. 2007

J. Phys. D: Appl. Phys.

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The power efficiency of organic light-emitting diodes was significantly improved by introducing a novel n-doping (4′7- diphyenyl-1, 10-phenanthroline: 33 wt% 8-hydroxy-quinolinato lithium) layer as an electron transport layer and a p-doping layer composed of 4, 4′, 4″-tris (3-methylphenylphenylamono) triphenylamine (m-MTDATA) and tetrafluro-tetracyano-quinodimethane (F4-TCNQ) as a hole transport layer. Hole-only and electron-only devices were demonstrated to observe an improvement in the conductivity of the transport layers. With this strategy, we demonstrated that the power efficiency was enhanced by ∼100%, luminous efficiency was enhanced by ∼54% while driving voltage was reduced by 32% as compared with the control device. We obtained a power efficiency of 4.44 Lm W−1, which is the best value so far reported for tris (8- hydroxyquinolinato) aluminium (Alq3)-based emitters. This improvement was ascribed to the improved conductivity of the transport layers and to the better charge balance in the emission zone.

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Section: Resultsmentioning

confidence: 94%

Section: Resultsmentioning

confidence: 99%

Highly power efficient organic light-emitting diodes based on p-doped and novel n-doped carrier transport layers

Khan¹,

Xu²,

Khizar-ul-Haq³

et al. 2007

J. Phys. D: Appl. Phys.

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“…Figure 1 shows the energy level diagram of the materials used in this study. Three sets of [23,24] and [25], respectively. electron-only devices with different cathodes were fabricated.…”

Section: Methodsmentioning

confidence: 99%

“…Energy level diagram of the materials used. HOMO and LUMO values of Bpy-OXD, BPhen and BCP have been taken from[23,24] and[25], respectively.…”

mentioning

confidence: 99%

Electron injection and transport mechanism in organic devices based on electron transport materials

Khan

Khizar-ul-Haq

et al. 2008

J. Phys. D: Appl. Phys.

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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.

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“…Also, one of the important properties of host materials is to balance electron and hole transporting ability [8][9] . The host materials are generally designed by introducing a well-known carbazole unit to obtain those properties, such as CBP (N,N'-dicarbazolyl-4,4'-biphenyl) [10] . However, a carbazole unit is a good electron donor which may induce an unbalanced carrier injection and transport into the emitting layer, resulting in a limited device performance.…”

Section: Introductionmentioning

confidence: 99%

High efficiency green phosphorescent OLEDs with long lifetime by using novel host material

Kim

et al. 2008

SPIE Proceedings

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We developed a novel host material, CheilGH-01 reinforced with electron transporting property to perform high luminance efficiency and low driving voltage with long lifetime in green phosphorescent OLED without HBL (hole blocking layer). The device with a structure of ITO/NPB/TCTA/Host:Ir(ppy) 3 /Balq/Alq 3 /Liq/Al using CheilGH-01 as a host showed better performance than the device with CBP as a host; At luminance of 1000 cd/m 2 , driving voltages, current efficiencies and power efficiencies are 5.4 V, 60 cd/A and 35 lm/W for CheilGH-01 and 7.2 V, 42 cd/A and 18.8 lm/W for CBP. It takes 240 hours for CheilGH-01 and 177 hours for CBP from the initial luminance of 3000 cd/m 2 to the luminance of 1500 cd/m 2 (55% of the initial). In the case of device with a structure of ITO/NPB/TCTA /Host:Ir(ppy) 3 /Alq 3 /Liq/Al, CheilGH-01 showed 300% enhancement in luminance efficiency and more than 800% longer lifetime than CBP; At luminance of 1000 cd/m 2 , driving voltages, current efficiencies and power efficiencies are 6.3 V, 51 cd/A and 26 lm/W for CheilGH-01 and 8.6 V, 21 cd/A and 7.8 lm/W for CBP. It takes 411 hours for CheilGH-01 and 82 hours for CBP from the initial luminance of 3000 cd/m 2 to the luminance of 1500 cd/m 2 . By using our novel host material, we are able to eliminate HBL from the conventional green phosphorescent OLED and still provide OLED with longer lifetime and excellent luminance efficiency.

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Study on electrical characteristics of organic electrophosphorescent devices based on new Ir complex

Cited by 18 publications

References 9 publications

Highly power efficient organic light-emitting diodes based on p-doped and novel n-doped carrier transport layers

Highly power efficient organic light-emitting diodes based on p-doped and novel n-doped carrier transport layers

Electron injection and transport mechanism in organic devices based on electron transport materials

High efficiency green phosphorescent OLEDs with long lifetime by using novel host material

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