tris(N-carbazolyl)triphenylamine Research Articles

Correlation between host material compositions and performances in organic white-light-emitting diodes with blue/orange/blue emitting stacked structure

Quantum efficiency, driving voltage, color stability and recombination zone of organic white-light-emitting diodes (OWLEDs) with blue/orange/blue stacked emitting structure were correlated with host structure of emitting layer. A mixed host structure of 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA) and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) was used in orange emitting layer and host composition was critical to device performances of OWLEDs. TPBI host structure was better than other host structures in terms of quantum efficiency and color stability, while TCTA shows poor quantum efficiency in spite of good color stability. TCTA:TPBI mixed host structure showed better driving voltage than other host structures. In addition, recombination zone in blue/orange/blue stacked OWLEDs could be controlled by changing host structure in orange light-emitting layer. OWLEDs with TPBI host in orange emitting layer showed high quantum efficiency of 10.3% at 1000 cd/m 2 with little change of Commission international De L’Eclairage coordinates of (0.32, 0.34) from 100 cd/m 2 to 10,000 cd/m 2.

Thermally Cross-Linkable Hole-Transporting Materials for Improving Hole Injection in Multilayer Blue-Emitting Phosphorescent Polymer Light-Emitting Diodes

One of the most challenging tasks in fabricating multilayer polymer light-emitting diodes (PLEDs) is to develop robust hole-transporting materials that possess matched energy level with indium tin oxide (ITO) anode and the highest occupied molecular orbital (HOMO) of light-emitting polymers to facilitate efficient hole injection and transport. In this article, a series of thermally cross-linkable 4,4′,4′′-tris(N-carbazolyl)triphenylamine (TCTA) derivatives have been synthesized to explore their function as efficient hole-transporting materials for blue-emitting electrophorphorescent devices. In particular, their excellent solvent resistance enables them to be used in the double hole-transporting layer (HTL) device configuration to facilitate cascade hole injection. The effects of cross-linking temperature and the functional group on the compatibility between two HTLs are investigated through optical and atomic force microscopy. When vinylbenzyl ether is used as the cross-linking group for TCTA, it shows t...

Small molecule interlayer for solution processed phosphorescent organic light emitting device

Using a 4,4′,4′′-tris( N-carbazolyl)-triphenylamine (TCTA) small molecule interlayer, we have fabricated efficient green phosphorescent organic light emitting devices by solution process. Significantly a low driving voltage of 3.0 V to reach a luminance of 1000 cd/m 2 is reported in this device. The maximum current and power efficiency values of 27.2 cd/A and 17.8 lm/W with TCTA interlayer (thickness 30 nm) and 33.7 cd/A and 19.6 lm/W with 40 nm thick interlayer are demonstrated, respectively. Results reveal a way to fabricate the phosphorescent organic light emitting device using TCTA small molecule interlayer by solution process, promising for efficient and simple manufacturing.

Relationship between dopant energy levels and device performances of triplet mixed host devices

Device performances of phosphorescent organic light-emitting diodes (PHOLEDs) with triplet mixed host structure were correlated with dopant energy levels and mixed host composition. A mixed host of 4,4′,4″-tris-( N-carbazolyl)triphenylamine (TCTA) and spirobifluorene type host (PH1) was used and three different dopants with different bandgap were doped in the mixed host. Optimum quantum efficiency was obtained in TCTA:PH1 (50:50) mixed host device in the case of green dopants, while the optimum host composition for red and orange dopants was TCTA:PH1 (25:75).

Triplet host engineering for triplet exciton management in phosphorescent organic light-emitting diodes

The device performances of green phosphorescent organic light-emitting diodes with a triplet mixed host emitting layer were correlated with the energy levels and composition of the host materials. Two hole-transport-type host materials, (4,4′-N,N′-dicarbazole)biphenyl (CBP) and 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA), were combined with two electron-transport-type host materials, 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBI) and PH1. The maximum quantum efficiency was obtained in the 5:5 mixed host in the case of TCTA:TPBI and TCTA:PH1, while CBP:PH1 showed the best performances in the 9:1 mixed host. The quantum efficiency of the green mixed host devices was improved by more than 50% compared with that of the corresponding single host devices.

Reduced efficiency roll-off in phosphorescent organic light emitting diodes by suppression of triplet-triplet annihilation

The authors investigate phosphorescent organic light emitting diodes comprising mixed films of fac tris(2-phenylpyridine) iridium dispersed in 4,4′,4′-tris(N-carbazolyl)-triphenylamine (TCTA) as emission layer (EML). Based on the results of photoluminescence experiments, they intermit the EML with thin neat layers of TCTA acting as an exciton blocking layer inside the EML which suppresses triplet-triplet annihilation. They show that this EML structure leads to an improved roll-off behavior: Starting at the initial external quantum efficiencies (IEQE) of 15.8% and 14.4% at low brightness for the reference and interlayer device, respectively, those structures yield critical current densities jc of 140mA∕cm2 and 270mA∕cm2 defining the current density of half-value IEQE.

Highly efficient white organic light emitting diodes comprising an interlayer to separate fluorescent and phosphorescent regions

White organic light emitting diodes combining the phosphorescent green and orange-red emitting systems fac tris(2-phenylpyridine) iridium doped 4,4′,4″-tris(N-carbazolyl)-triphenylamine (TCTA) and iridium(III)bis(2-methyldibenzo-[f,h]quinoxaline)(acetylacetonate) doped N,N′-di(naphthalen-1-yl)-N,N′-diphenyl-benzidine with the blue fluorescent dye 2,2′,7,7′-tetrakis(2,2-diphenylvinyl)spiro-9,9′-bifluorene (Spiro-DPVBi) are presented. By introducing a thin layer of coevaporated TCTA and 2,2′,2″ (1,3,5-benzenetriyl) tris-[1-phenyl-1H-benzimidazole] between the phosphorescent and the fluorescent region, both singlet and triplet excitons are confined efficiently, whereas charge carriers still pass easily this interlayer. Furthermore, the interlayer suppresses Dexter transfer of the phosphorescent excitons to the nonradiative triplet state of Spiro-DPVBi. Best devices reach a current efficiency of 16.3cd∕A at 100cd∕m2 and a color rendering index of 85 at warm white CIE chromaticity coordinates of (0.47, 0.42). Due to the use of electrically doped charge transport layers, 100cd∕m2 are obtained at 2.95V with a power efficiency of 17.4lm∕W.