Enhancing Horizontal Ratio of Transition Dipole Moment in Homoleptic Ir Complexes for High Outcoupling Efficiency of Organic Light-Emitting Diodes.

The light-emitting dipole orientation (EDO) of a phosphorescent emitter is a key to improving the external quantum efficiency (EQE) of organic light-emitting diodes (OLEDs) without structural modification of the device. Here, four homoleptic Ir complexes as a phosphorescent emitter are systematically designed based on the molecular structure of tris(2-phenylpyridine)iridium(III) (Ir(ppy)3 ) to control the EDO. Trimethylsilane, methyl, 2-methylpropyl, and cyclopentylmethyl group substituted to pyridine ring of the ligand contribute to the improvement of the EDO from 76.5% for Ir(ppy)3 to 87.5%. A linear relationship between the EDO and the aspect ratio (geometric anisotropy factor) is founded, implying the importance of the effective area for the nonbonding force between host and dopant molecules. Also, it is investigated that the EDO enhancement mainly originates from the vertical alignment of the C3 axis of molecule in the substrate axis rather than the change in the direction of the transition dipole alignment in the molecular axis. The optical simulation reveals that the outcoupling efficiency of phosphorescent OLEDs adopting new dopants reaches 38.4%. The green OLEDs exhibiting 28.3% of EQE, 103.2 cd A-1 of current efficiency, and 98.2 lm W-1 of power efficiency are demonstrated, which is understood to have little electrical loss.

Red Phosphorescent Bis-Cyclometalated Iridium Complexes with Fluorine-, Phenyl-, and Fluorophenyl-Substituted 2-Arylquinoline Ligands.

Red phosphorescent iridium(III) complexes based on fluorine-, phenyl-, and fluorophenyl-substituted 2-arylquinoline ligands were designed and synthesized. To investigate their electrophosphorescent properties, devices were fabricated with the following structure: indium tin oxide (ITO)/4,4',4''-tris[2-naphthyl(phenyl)amino]triphenylamine (2-TNATA)/4,4'-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB)/4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP): 8% iridium (III) complexes/bathocuproine (BCP)/tris(8-hydroxyquinolinato)aluminum (Alq3)/8-hydroxyquinoline lithium (Liq)/Al. All devices, which use these materials showed efficient red emissions. In particular, a device exhibited a saturated red emission with a maximum luminance, external quantum efficiency, and luminous efficiency of 14200 cd m(-2), 8.44%, and 6.58 cd A(-1) at 20 mA cm(-2), respectively. The CIE (x, y) coordinates of this device are (0.67, 0.33) at 12.0 V.

The effect of a charge control layer on the electroluminescent characteristic of blue and white organic light-emitting diodes.

We investigated blue fluorescent organic light-emitting diode (OLED) with a charge control layer (CCL) to produce high efficiency and improve the half-decay lifetime. Three types of devices (device A, B, and C) were fabricated following the number of CCLs within the emitting layer (EML), maintaining the thickness of whole EML. The CCL and host material, 2-methyl-9,10-di(2-naphthyl)anthracene, which has a bipolar property, was able to control the carrier movement with ease inside the EML. Device B demonstrated a maximum luminous efficiency (LE) and external quantum efficiency (EQE) of 9.19 cd/A and 5.78%, respectively. It also showed that the enhancement of the half-decay lifetime, measured at an initial luminance of 1,000 cd/m2, was 1.5 times longer than that of the conventional structure. A hybrid white OLED (WOLED) was also fabricated using a phosphorescent red emitter, bis(2-phenylquinoline)-acetylacetonate iridium III doped in 4,4'-N,N'-dicarbazolyl-biphenyl. The property of the hybrid WOLED with CCL showed a maximum LE and an EQE of 13.46 cd/A and 8.32%, respectively. It also showed white emission with Commission International de L'Éclairage coordinates of (x = 0.41, y = 0.33) at 10 V.

Red fluorescent materials based on julolidine/chromene with the bulky tert-butyl and trimethylsilyl substituents for organic light-emitting diodes.

In this work, we designed and synthesized two red emitters 2-(6,8-di-tert-butyl-2-(2-(1,1-dimethyl-7-(trimethylsilyl)-7-((trimethylsilyl)methyl)-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-9-yl)vinyl)-4H-chromen-4-ylidene)malononitrile (Red 1) and 2-(6,8-di-tert-butyl-2-(2-(1,1,7-trimethyl-7-t-butyl)-1,2,3,5,6,7-hexahydropyrido[3,2,1-ij]quinolin-9-yl)vinyl)-4H-chromen-4-ylidene)malononitrile (Red 2). To explore the electro-luminescence properties of these materials, multilayered OLEDs using these materials as dopants in a Alq3 host were fabricated. Particularly, by using Red 1 as a dopant in emitting layer, device 1 showed the luminous and power efficiencies of 0.81 cd/A and 0.43 lm/W at 20 mA/cm2, respectively. The CIE coordinates of this device was (0.65, 0.34) at 7.0 V, which is close to the NTSC standard CIE coordinates of (0.67,0.32) for red emission.

Improved efficiency of red phosphorescent organic light-emitting diodes with combination of heterojunction and mixed host structure.

We report an improvement of efficiency in red phosphorescent organic light-emitting diodes (PHOLEDs) based on a combination of heterojunction (HJ) structure and mixed host (MH) system using a phosphorescent red emitter: bis(2-phenylquinolinato)-acetylacetonate iridium III [Ir(pq)2(acac)] doped in 4,4,N,N'-dicarbazolebiphenyl (CBP) of hole transport type host material and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) of electron transport type host material. This combination device resulted in an effective electron and hole balance and distribution of the recombination zone. Therefore, highly efficient red PHOLEDs with maximum luminous efficiency and external quantum efficiency of 21.93 cd/A and 14.09% were achieved. Moreover, the combination device showed a power efficiency of 9.51 lm/W, which is higher than 7.61 lm/W in the control device at a luminance of 1000 cd/m2.

Enhanced efficiency of blue phosphorescent organic light-emitting diode base on triple-emitting layer with mixed host system.

We report an improvement of efficiency in blue phosphorescent organic light-emitting diodes (PHOLEDs) based on triple-emitting layer (T-EML) with mixed host (MH) system using a phosphorescent blue emitter: iridium(III)bis[(4,6-di-fluoropheny)-pyridinato-N,C2]picolinate (Flrpic) doped in N,N'-dicarbazolyl-3,5-benzene (mCP) of hole transport-type host material and 1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi) of electron transport-type host material. This T-EML device resulted in both an effective electron and hole balance and efficient distribution of the recombination zone. As a result, the property of T-EML device which demonstrated a maximum luminous efficiency of 24.45 cd/A and a external quantum efficiency of 10.9%. It also showed a high maximum power efficiency of 13.82 lm/W, which is approximately two times higher than that of the control device.

Blue organic light-emitting diodes based on new bipolar anthracene derivatives containing pyridine.

A series of bipolar anthracene derivatives containing pyridine as an electron withdrawing group and cabazole, triphenylamine and indole as electron donating groups were synthesized and characterized. Particularly, Device E, 9-(4'-(10-(pyridin-2-yl)anthracen-9-yl)biphenyl-4-yl)-9H-carbazol exhibits a high-efficient deep-blue EL emission with the luminous efficiency (LE) of 2.31 cd/A, power efficiency (PE) of 1.39 lm/W and quantum efficiency (QE) of 1.94% at 500 nit. This compound shows the maximum wavelength of the electroluminescence (EL) at 467 nm and the CIE x, y coordinates of (0.16,0.14) at 6 V.

Efficient red phosphorescent OLEDs using Ir(III) complexes based on bezoylphenylpyridine and the various ancillary ligands.

A series of red phosphorescent Ir(III) complexes 1-5 based on benzoylphenylpyridine and various ancillary ligands were synthesized and their photophysical properties were investigated. The EL efficiencies were quite sensitive to the structural features of the dopants in the emitting layers. Particularly, using complex 5 as a dopant in emitting layer, a high-efficiency orange-red OLED was fabricated, showing the maximum luminance of 16,900 cd/m2 at 12 V, the luminous efficiency of 12.8 cd/A, the power efficiency of 4.48 lm/W, the external quantum efficiency of 9.65% at 20 mA/cm2 and CIE x,y coordinates of (0.609, 0.390) at 12 V.

Triphenylamine substituted anthracene derivatives for blue organic light-emitting diodes.

A series of bipolar anthracene derivatives containing triphenylamine as an electron donating group and pyridine, quinoline, isoquinoline and benzothiazole as electron withdrawing groups were synthesized and characterized. Particularly, a material, 9-quinolinyl-10-triphenylamin anthracene (3) exhibits a highly efficient sky-blue EL emission with the luminous efficiency (LE) of 9.36 cd/A, power efficiency (PE) of 5.94 lm/W and quantum efficiency (QE) of 4.23% at 500 nit. This material shows the maximum wavelength of the electroluminescence (EL) at 486 nm and the CIE x, y coordinates of (0.17, 0.36) at 6 V.

Undoped blue organic light-emitting diodes using 2-diphenylaminofluoren-7-ylstyryl derivatives.

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).

Phosphorescent white organic light-emitting diodes by electron transporting layer engineering.

The authors describe the fabrication of white organic light-emitting diodes (WOLEDs) with dual electron transporting layers (D-ETL) using 2,9-dimethyl-4,7-diphenyl-1,10-phenanhroline/ 4,7-diphenyl-1,10-phenanthroline (BPhen) and bis-(2-methyl-8-quinolinolate)-4-(phenylphenolato) aluminum/BPhen. Stepwise D-ETL easily transports electrons easily to the emitting layer and reduces the leakage of electrons. Therefore, WOLEDs with D-ETL show higher external quantum efficiency (EQE) when compared to a control WOLED with a single ETL device. The optimized WOLEDs showed a peak EQE of 13.0%, luminous efficiency of 27.4 cd/A, and Commission Internationale de L'Eclairage coordinates of (0.40, 0.39) at 1000 cd/m2.

Efficient green phosphorescent organic light-emitting diodes depending on concentration of lithium quinolate in electron transport layer.

Systematic studies on carrier injection and transport are very important for achieving high efficiency in OLEDs. We demonstrate excellent green phosphorescent organic light-emitting diodes (OLED) with lithium quinolate (Liq) doped in 1,3,5-tris(N-phenylbenzimidazole-2-yl) benzene (TPBi) as the electron transport layer (ETL). The doping concentration of Liq was varied from 0% to 10%. The optimized green phosphorescent OLED with 5% Liq in the ETL showed the best efficiencies, which were maximum luminous efficiency, power efficiency, and quantum efficiency of 65.76 cd/A, 57.39 Im/W, and 20.03%, respectively. Moreover, high triplet energy states of TCTA and TPBi as a triplet exciton-blocking layer (TEBL) played a role in efficient exciton confinement.

Phosphorescence white organic light-emitting diodes with single emitting layer based on isoquinolinefluorene-carbazole containing host.

We have demonstrated a stable phosphorescent white organic light-emitting diodes (WOLEDs) using an orange emitter, Bis(5-benzoyl-2-(4-fluorophenyl)pyridinato-C,N) iridium(III)acetylacetonate [(Bz4Fppy)2Ir(III)acac] doped into a newly synthesized blue host material, 2-(carbazol-9-yl)-7-(isoquinolin-1-yl)-9,9-diethylfluorene (CzFliq). When 1 wt.% (Bz4Fppy)2Ir(III)acac was doped into emitting layer, it was realized an improved EL performance and a pure white color in the OLED. The optimum WOLED showed maximum values as a luminous efficiency of 10.14 cd/A, a power efficiency of 10.24 Im/W, a peak external quantum efficiency 4.07%, and Commission Internationale de L'Eclairage coordinates of (0.34, 0.39) at 8 V.

N,N-(diphenylamino)fluorenylstyrene derivatives with the various heteroatom-containing moieties for blue organic light-emitting diodes.

A series of blue fluorescent materials 1-6 based on N, N-diphenyl aminofluorene styryl derivatives with six heteroatoms (PhOPh, PhSPh, PhSePh, PhPPh2, thiophene and dibenzothiophene), were synthesized and multilayer devices were fabricated. Interestingly, the EL efficiencies were very sensitive to the structural features of dopants in the emitting layers. Particularly, by using 1 as a dopant in emitting layer, a high-efficiency blue OLED was fabricated, showing the maximum luminance of 10420 cd/m2 at 11 V, the luminous efficiency of 8.6 cd/A at 20 mA/cm2, the power efficiency of 3.4 Im/W at 20 mA/cm2 and had a blue color with the CIE coordinates of (0.147, 0.156) at 8.0 V.

Red fluorescent emitting materials based on di-tert-butyl chromene derivatives for organic light-emitting diodes.

In this paper are described two di-tert-butyl chromene-containing red fluorescent materials (Red 1 and Red 2). To explore the electroluminescence properties of these materials, multilayered OLEDs using these materials as dopants in a Alq3 host were fabricated. In particular, a device using Red 2 as the dopant material showed maximum luminous efficiencies and power efficiencies of 1.14 cd/A and 0.58 Im/W, respectively. The CIEx,y coordinates of this device were (0.67, 0.32) at 7.0 V.

Diphenylamino-fluorenylethylene derivatives for highly efficient blue organic light-emitting diodes.

Highly efficient blue organic light-emitting diodes (OLEDs) were developed using diphenylamino-fluorenylethylene derivatives. In particular, OLEDs using compound 3 as a dopant in the emitting layer showed a maximum luminance of 12940 cd/m2 at 10 V; a luminous efficiency of 12.68 cd/A at 20 mA/cm2; a power efficiency of 5.24 Im/W at 20 mA/cm2, and CIE(x,y) coordinates of 0.181, 0.295 at 10 V. Furthermore, a deep blue OLED using dopant 2 with CIE coordinates of (0.154, 0.129) exhibited a maximum luminance of 5315 cd/m2 at 10 V; a luminous efficiency of 4.11 cd/A at 20 mA/cm2, and a power efficiency of 1.66 Im/W at 20 mA/cm2.

Efficient deep-blue organic light-emitting diodes using double-emitting layer.

Efficient deep-blue organic light-emitting diodes were demonstrated using 1,4-tetranaphthalene doped in double-emitting layers (D-EMLs) consisting of 2-methyl-9,10-di(2-naphthyl)anthracene and 4'-(dinaphthalen-2-yl)-1,1'-binaphthyl as blue hosts. The device with D-EML exhibits good confinement of holes and electrons, as well as a broad recombination zone. The optimized device showed a peak current efficiency of 3.67 cd/A, a peak external quantum efficiency of 3.97%, and Commission Internationale de L'Eclairage coordinates of (0.16, 0.10).

Highly efficient red phosphorescent organic light-emitting devices using iridium(III) complexes based on 2-(biphenyl-3-yl)quinoline derived ligands.

Red phosphorescent emitters were synthesized based on Ir(III) phenylquinoline complexes for applications to OLEDs. Ir(III) complexes 1-3 were based on 2-(biphenyl-3-yl)-quinoline units connected to various phenyl groups such as 5-phenyl, 5-(4-fluorophenyl), and 6-phenyl groups. The EL efficiencies were quite sensitive to the structural features of the dopants in the emitting layers. In particular, a high-efficiency red OLED was fabricated using complex 1 as the dopant in the emitting layer. This OLED showed a maximum luminance, luminous efficiency, power efficiency, external quantum efficiency and CIE(x,y) coordinates of 21,600 cd/m2 at 16 V, 11.80 cd/A at 20 mA/cm2, 3.57 Im/W at 20 mA/cm2, 10.90% at 20 mA/cm2, and (x = 0.63, y = 0.32) at 12 V, respectively.

Efficient triplet exciton confinement of blue- and white-organic light emitting diodes using a new host material.

We have demonstrated lower driving voltage and efficient blue phosphorescent organic light emitting diodes (PHOLEDs) using iridium(III) bis[(4,6-di-fluoropheny)-pyridinato-N,C2] picolinate (Flrpic) doped in new host material 9-(4-(triphenylsilyl)phenyl)-9H-carbazole (SPC) and 2,2',2"-(1,3,5-benzenetryl)tris(1-phenyl)-1H-benzimidazol (TPBi) as double-emitting layer (D-EML) system. The D-EML was employed to have good electron transportability and exciton confinement. Additionally, we fabricated white organic light-emitting diode (WOLED) using a phosphorescent red emitter; bis(2-phenylquinolinato)-acetylacetonate iridium III (Ir(pq)2acac) doped in SPC and TPBi as D-EML. The properties of white device exhibited a maximum luminous efficiency of 19.03 cd/A, a maximum external quantum efficiency of 9.91%, and a maximum power efficiency of 12.30 lm/W. It also showed white emission with CIE(x,y) coordinates of (x = 0.38, y = 0.37) at 8 V.

Red phosphorescent organic light-emitting diodes based on the simple structure.

We demonstrated that the simple layered red phosphorescent organic light-emitting diodes (OLEDs) are possible to have high efficiency, low driving voltage, stable roll-off efficiency, and pure emission color without hole injection and transport layers. We fabricated the OLEDs with a structure of ITO/CBP doped with Ir(pq)2(acac)/BPhen/Liq/Al, where the doping concentration of red dopant, Ir(pq)2(acac), was varied from 4% to 20%. As a result, the quantum efficiencies of 13.4, 11.2, 16.7, 10.8 and 9.8% were observed in devices with doping concentrations of 4, 8, 12, 16 and 20%, respectively. Despite of absence of the hole injection and transport layers, these efficiencies are superior to efficiencies of device with hole transporting layer due to direct hole injection from anode to dopant in emission layer.