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We developed highly efficient quantum dot light-emitting devices (QD-LEDs) by improving the charge balance with triple hole injection and transport layers consisted of MoO3/poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD)/poly(9-vinylcarbazole) (PVK). The hole injection layer was prepared by evaporating MoO3. Poly-TPD and PVK were spin-coated as hole transport layers. The stepwise energy level of MoO3/poly-TPD/PVK enhanced the hole injection from anode to QD emitters. Tris[2,4,6-trimethyl-3-(pyridine-3-yl)phenyl]borane (3TPYMB) was used as an electron transport layer (ETL) because of its relatively high electron mobility and deep lowest unoccupied molecular orbital (LUMO) level. We achieved high external quantum efficiency of 8.2% by enhancing hole injection into the QD layer in the organic ETL-based green QD-LEDs. [ABSTRACT FROM AUTHOR]

We have fabricated solution processed organic light-emitting devices (OLEDs) with various hole transporting materials (HTMs) on the plastic substrate. The device structure was ITO/HTM:Ir(2-phq)31wt%:FIrpic 5wt% (50 nm)/TAZ (50 nm)/LiF (0.5 nm)/Al (100 nm). 4,4′-bis(carbazol-9-yl)biphenyl (CBP), di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane (TAPC), poly[N,N'-bis(4-butylphenyl)-N,N'-bis(phenyl)-benzidine] (poly-TPD), and poly(9-vinylcarbazole) (PVK) were used for HTM. Phosphorescent orange-red emitting Ir(2-phq)3and blue emitting FIrpic guest molecules were mixed with the HTMs and solvents. OLED with TAPC exhibited the maximum current efficiency of 17.4 cd/A at 0.42 mA/cm2. [ABSTRACT FROM AUTHOR]

We have investigated the recombination zone in the phosphorescent white organic light-emitting devices with single host structure of multi-emission layers. Blue, green, and orange-red phosphorescent emitters were doped into the separate layers of single host material for fabricating the white devices with multi-emission layers. The electroluminescence spectrum was substantially modified by the shift of the recombination zone that was dependent upon the thickness of the electron transport layer. We investigated the recombination zone shift in terms of electric field distribution and carrier injection. A maximum external quantum efficiency of 15.9% and a maximum power efficiency of 28.9 lm/W were achieved by optimizing the recombination zone. [ABSTRACT FROM AUTHOR]

Abstract: We have developed red phosphorescent organic light-emitting devices operating at low voltages by using triphenylphosphine oxide (Ph3PO) and 4,4′-bis(2,2′-diphenylvinyl)-1,1′-biphenyl (DPVBi) electron transport layers. 4,4′-bis(N-carbazolyl)-1,1′-biphenyl (CBP) and tris-(1-phenylisoquinolinolato-C 2,N) iridium(III) [Ir(piq)3] were used as host and guest materials, respectively. Small voltage drops across the electron transport layers and direct injection of holes from 4,4′,4″-tris[N-(2-naphthyl)-N-phenyl-amino]-triphenylamine (2-TNATA) hole transport layer into the Ir(piq)3 guests are responsible for the high current density at low voltage, resulting in a high luminance of 1000cd/m2 at low voltages of 2.8–3.0V in devices with a structure of ITO/2-TNATA/CBP:Ir(piq)3/DPVBi/Ph3PO/LiF/Al. [Copyright &y& Elsevier]

Abstract: We have developed highly efficient blue phosphorescent organic light-emitting devices comprising of two organic layers. Hole transporting 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) was used as an emitting host for iridium(III)bis[(4,6-di-fluorophenyl)-pyridinato-N,C 2′]picolinate (FIrpic) guest. In our bilayer system, the host–guest energy transfer process leads to a low optimal doping concentration of 2wt%, while the better charge balance is achieved by the better electron injection into the host layer from electron transport layer. Using these bilayer structures, we demonstrate a maximum current efficiency of 34cd/A in the device structure of ITO/TAPC: FIrpic (30nm, 2wt%)/3-(4-biphenyl-yl)-4-phenyl-5-(4-tert-butylphenyl)-1,2,4-triazole (50nm)/LiF/Al. [Copyright &y& Elsevier]

Abstract: We have developed highly efficient blue phosphorescent organic light-emitting devices with thin 1,1-bis[(di-4-tolyamino)phenyl]cyclohexane (TAPC) layers. We used simple three organic layers: TAPC, iridium(III) bis[[4,6-di-fluorophenyl]-pyridinato-N,C2′] picolinate (FIrpic) doped N,N′-dicarbazolyl-3,5-benzene (mCP), and 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP) layers. The device structure was ITO/TAPC (x nm)/mCP:FIrpic (5nm, 10%)/BCP (55nm)/LiF/Al. The 4nm TAPC device shows current efficiency and power efficiency of 34cd/A and 15.1lm/W, respectively, at a luminance of 1540cd/m2. We investigate the effect of TAPC thickness on the current efficiency, power efficiency, driving voltage, and electroluminescence characteristics. [Copyright &y& Elsevier]

Highlights: [•] Color stability of hybrid white OLEDs has been investigated. [•] EL spectra, CIE coordinates, and recombination zone have been investigated. [•] Current conduction and emission mechanisms were investigated. [•] The color stability by compensating blue fluorescent layer was investigated. [•] High color-stability and efficiency were obtained. [ABSTRACT FROM AUTHOR]

We have developed highly efficient inverted phosphorescent organic light-emitting devices (OLEDs) using ZnO nanoparticles (NPs). The wurtzite structured ZnO NPs having an average particle size of about 5 nm were synthesized by solution-precipitation method. The inverted phosphorescent OLEDs with a tris(2-phenylpyridine) iridium(III) emitter have fabricated using ZnO NPs and 2,2',2"-(1,3,5-benzinetriyl)-tris-(1-phenyl)− 1-H-benzimidazole (TPBi) electron transport layer. ZnO NPs effectively inject electrons from cathode to the electron transport layer. The maximum external quantum efficiency and current efficiency of the phosphorescent inverted OLEDs with ZnO NPs were 15.8% and 55.1 cd/A, respectively. • We developed highly efficient inverted phosphorescent OLEDs with ZnO nanoparticles. • ZnO nanoparticles were used as an electron injection layer. • ZnO NPs efficiently inject electrons from cathode to the electron transport layer. • The maximum external quantum efficiency of the inverted device was 15.8%. [ABSTRACT FROM AUTHOR]

We have investigated substantial drop of external quantum efficiency (EQE) at liquid nitrogen temperature in a bilayer blue phosphorescent organic light emitting device with a structure of ITO/TAPC:FIrpic/TAZ/LiF/Al, where TAPC, FIrpic, and TAZ represent 1,1-bis[(di-4-tolylamino)phenyl]cyclohexane, iridium(III)bis[(4,6-difluorophenyl)-pyridinato-N,C 2′ ]picolinate, and 3-(biphenyl-4-yl)-4-phenyl-5-(4-tert-butyl-phenyl)-1,2,4-triazole, respectively. The device exhibits a high EQE of 17.2% at room temperature although it has a simple bilayer structure. However, the quantum efficiency drops drastically to 0.8% at liquid nitrogen temperature. We studied this drastic drop of EQE in viewpoints of carrier conduction, carrier recombination, photoluminescence quantum efficiency, and energy transfer. [ABSTRACT FROM AUTHOR]