Author Affiliations
Abstract
1 Department of Green Energy & Semiconductor Engineering, Hoseo University, Asan 31499, Korea
2 R&D Center, A-PRO Co. Ltd., Gunpo 15830, Korea
3 Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong 070, China
4 Department of Engineering Physcis, McMaster University, Hamilton, Ontario L8S 4L7, Canada
In order to realize single emissive white phosphorescent organic light-emitting devices (PHOLEDs) with three color phosphorescent dopants (red, green, and blue), the energy transfer between the host material and the three dopants, as well as the among the three dopants themselves, should be considered and optimized. To explore the effect of red phosphorescent dopant on the color rendering index (CRI), the authors investigate the wavelength position of the maximum emission peak from three phosphorescent dopants. The CRI and luminous efficiency of white PHOLED in which Ir(pq)2(acac) acts as the red phosphorescent dopant are found to be greater than those of devices prepared using Ir(piq)3 and Ir(btp)2(acac) as the emission spectrum has a relatively high intensity near the human perception of blue, red, and green wavelengths. Furthermore, we demonstrate that the performance of the three dopants is related to the absorption characteristics of the red phosphorescent dopant. With a maximum emission peak at 600 nm, Ir(pq)2(acac) has a higher intensity in the concave section between 550 and 600 nm seen for red and blue dopants. In addition, the long metal-to-ligand charge transfer (MLCT) absorption tail of Ir(pq)2(acac) overlaps with the emission spectra of the green dopant, enhancing emission. Such energy transfer mechanisms are confirmed to optimize white emission in the single emissive white PHOLEDs.
160.4890 Organic materials 300.1030 Absorption 260.2160 Energy transfer Chinese Optics Letters
2017, 15(5): 051602
Author Affiliations
Abstract
1 Department of Green Energy and Semiconductor Engineering, Hoseo University, Asan 330-713, South Korea
2 Department of Engineering Physics, McMaster University, Hamilton, Ontario L8S4L8, Canada
In this Letter, blue phosphorescence organic light-emitting diodes (PHOLEDs) employ structures for electron and/or hole confinement; 1,3,5-tris(N-phenylbenzimiazole-2-yl)benzene is used as a hole confinement layer and tris-(phenylpyrazole)iridium [Ir(ppz)3] is utilized for an electron confinement layer (ECL). The electrical and optical properties of the fabricated blue PHOLEDs with various carrier-confinement structures are analyzed. Structures with a large energy offset between the carrier confinement and emitting layers enhance the charge-carrier balance in the emitting region, resulting from the effective carrier confinement. The maximum external quantum efficiency of the blue PHOLEDs with the double-ECLs is 24.02% at 1500 cd/m2 and its luminous efficiency is 43.76 cd/A, which is 70.47% improved compared to the device without a carrier-confinement layer.
230.3670 Light-emitting diodes 230.0230 Optical devices 230.4170 Multilayers 230.4205 Multiple quantum well (MQW) modulators 230.5590 Quantum-well, -wire and -dot devices Chinese Optics Letters
2015, 13(3): 032301
Author Affiliations
Abstract
1 Department of Green Energy &
2 Semiconductor Engineering, Hoseo University, Asan, South Korea
We fabricate white phosphorescent organic light-emitting diodes (PHOLEDs) with three dopants and double emissive layer (EML) to achieve color stability. The white PHOLEDs use FIrpic dopant for blue EML (B-EML), and Ir(ppy)3:Ir(piq)3 dopants for green:red EML (GR-EML) with N,N.'-dicarbazolyl-3, 5-benzene (mCP) as host material. Thicknesses of B-EML and GR-EML are adjusted to form a narrow recombination zone at two EML's interface and charge trapping happens in EML according to wide highest occupied molecular orbital and/or lowest unoccupied molecular orbital energy band gap of mCP and smaller energy band gap of dopants. The total thickness of both EMLs is fixed at 30 nm in the device structure of ITO (150 nm)/MoO3 (2 nm)/N,N'-diphenyl-N,N'-bis(l-naphthyl-phenyl)-(l,l'-biphenyl)-4, 4'-diamine (70?nm)/mCP:Firpic-8.0% (12?nm)/mCP:Ir(ppy)3-3.0%:Ir(piq)3-1.5% (18 nm)/2',2',2''-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (30 nm)/8-hydroxyquinolinolato-lithium (2 nm)/Al (120 nm). White PHOLED shows 18.25 cd/A of luminous efficiency and white color coordinates of (0.358 and 0.378) at 5000 cd/m2 and color stability with slight CIEXY change of (0.028 and 0.002) as increasing luminance from 1000 to 5000 cd/m2.
300.2140 Emission 300.6170 Spectra 330.1690 Color 230.3670 Light-emitting diodes Chinese Optics Letters
2014, 12(10): 102302
