Cubic (zinc-blende) InGaN/GaN double-heterostructure LEDs were fabricated on GaAs (001) substrates. The device performance and crystal quality were investigated. The emission wavelength was controlled by the In content in the cubic InGaN active layer. The violet-blue electroluminesence was observed around 435 nm with a FWHM of 55 nm from a cubic In 0.07 Ga 0.93 N/GaN DH LED. The forward voltage was 4.9 V at 20 mA and the reverse leakage current was 5 mA at ±10 V. X-ray reciprocal space mapping measurement was performed to investigate the phase purity and strain in InGaN/GaN heterostructure. The mixing of the stable hexagonal phase in the cubic GaN was observed and the hexagonal phase content was about 10%. In-situ spectroscopic ellipsometry measurement showed that most of the mixed hexagonal domains were likely to be formed in the Mg-doped GaN layer. In addition, the anisotropic lattice relaxation occurred in the InGaN active layer. The elimination of the hexagonal phase inclusions plays an important role for the realization of high performance devices.
To obtain a saturated blue phosphorescent material with a good color purity, we have synthesized the new blue emitting iridium complexes with 2, 6-difluoro-3-(4-methylpyridin-2-yl)pyridine (4-Me-dfpypy) as a main ligand. We expected that the LUMO energy levels of the complex might increase upon introduction of an electron donating group such as a methyl group to the pyridyl moieties of the ligand, leading to a wide energy gap of the complex to give the saturated blue emission. We have also introduced a variety of the ancillary ligands to the iridium center to compare the effect of the ancillary ligards on the emission of their complexes. The resulting iridium complexes, Ir(4-Me-dfpypy)3, Ir(4-Me-dfpypy)2(acac), Ir(4-Me-dfpypy)2(pic) and Ir(4-Me-dfpypy)2(trzl-CH3) where acac, pic, and trzl-CH3 represent acetylacetonate, picolinate, and 2-(5-methyl-2H-1,2,4-triazol-3-yl) pyridinate, respectively exhibited the blue emission at 451, 447, 440 and 425 nm in CH2Cl2 solution. The organic light emitting device (OLED) employing homoleptic Ir(4-Me-dfpypy), as the blue dopant was prepared and their electroluminescence was investigated. Ir(4-Me-dfpypy)3 exhibited the blue emission of CIE coordinates (0.22, 0.32).
The device performance of red organic light-emitting diodes (OLEDs) was dramatically improved by co-doping of the red fluorescent material of (2Z,2'Z)-3,3'-[4,4"-bis(dimethylamino)-1,1':4',1"-terphenyl-2',5'-diyl]-bis(2-phenylacrylonitrile) (ABCV-P) with the hole transport material of N'-bis-(1-naphyl)-N,N'-diphenyl-1,1 '-biphenyl-4,4'-diamine (NPB) and the electron transport material of bis(2-methyl-8-quninolinato)-4-phenylphenolate aluminum (BAlq). The device structures were ITO/NPB/emitting layers/BAlq/Liq/Al in which the emitting layers were MADN:ABCV-P (40%) (device A), MADN:ABCV-P (40%):NPB (10%) (device B), MADN:ABCV-P (40%):BAlq (10%) (device C) and MADN:ABCV-P (40%):NPB (10%):BAlq (10%) (device D), respectively. The device D co-doped with NPB and BAlq exhibited maximum luminance of 9784 cd/m2, maximum luminous efficiency of 2.82 cd/A and maximum quantum efficiency of 3.19%, respectively, whereas those of the device A doped with only ABCV-P were 7563 cd/m2, 1.98 cd/A and 1.99%.
Blue fluorescent materials based on diphenylaminofluorenylstyryl derivatives connected with the various end-capping aromatic groups were synthesized and characterized. An OLED, using (E)-9,9-diethyl-7-(4-(4-fluoronaphthalen-1-yl)styryl)-N,N-diphenyl-9 H-fluoren-2-amine(5) in emitting layer, was fabricated. This device showed the highly efficient blue emission with the maximum luminance of 5138 cd/m2, the luminous efficiency of 3.92 cd/A, the power efficiency of 3.17 lm/W, the external quantum efficiency of 2.90% at 20 mA/cm2 and CIE x, y coordinates of (0.14, 0.17).
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.