Seok Jae Lee

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.

Synthesis of Ir(III) Complexes Containing Meta-Carbonylated Phenylpyridine Ligand for Phosphorescent Organic Light-Emitting Diodes

The photophysical characteristics of phosphorescent Ir(III) complexes 1–3 were investigated to determine their suitability as candidates for green light-emitting materials for OLEDs. To evaluate the EL properties of using these compounds as dopant in the emitting layer, multilayered devices were designed as green-light-emitting device having the following configuration: ITO/NPB (30 nm)/Ir(III) complexe 1 (5 and 10 wt.%) doped in CBP (30 nm)/BCP (10 nm)/Alq3 (40 nm)/Liq/Al were fabricated. An OLED device employing 1 as a dopant exhibits the performance with a maximum luminance of 46000 cd/m2 at 14.0 V. The luminous efficiency, power efficiency were 17.3 cd/A, 6.97 lm/W at 20 mA/cm2, respectively. Also, this device shows green emission with CIE coordinates of (0.247, 0.594) at 10.0 V.

Effect of a broad recombination zone with a triple-emitting layer on the efficiency of blue phosphorescent organic light-emitting diodes

AbstractThe device characteristics of blue phosphorescent organic lightemitting diodes (PHOLEDs) with a broad recombination region within emitting layers (EMLs) were investigated by changing the combination and the composition of the host materials. Six types of devices were fabricated with the novel host material 9-(4-(triphenylsilyl)phenyl)-9H-carbazole, hole transport-type host material N,N′-dicarbazolyl-3,5-benzene, and electron transporttype host material 2,2′,2″-(1,3,5-benzenetriyl)tris-[1-phenyl-1H-benzimidazole] as diverse EML structures. Balanced chargecarrier injection and a distributed recombination zone within EMLs were achieved through a triple-emitting layer (T-EML). The properties of a device with a T-EML using a stepwise structure without any mixed host system were found to be superior to the other PHOLEDs. This can be explained in terms of improved charge balance and triplet-exciton confinement within the broad recombination region.n

Flexible bottom-emitting white organic light-emitting diodes with semitransparent Ni/Ag/Ni anode.

We fabricated a flexible bottom-emitting white organic light-emitting diode (BEWOLED) with a structure of PET/Ni/Ag/Ni (3/6/3 nm)/ NPB (50 nm)/mCP (10 nm)/7% FIrpic:mCP (10 nm)/3% Ir(pq)(2) acac:TPBi (5 nm)/7% FIrpic:TPBi (5 nm)/TPBi (10 nm)/Liq (2 nm)/ Al (100 nm). To improve the performance of the BEWOLED, a multilayered metal stack anode of Ni/Ag/Ni treated with oxygen plasma for 60 sec was introduced into the OLED devices. The Ni/Ag/Ni anode effectively enhanced the probability of hole-electron recombination due to an efficient hole injection into and charge balance in an emitting layer. By comparing with a reference WOLED using ITO on glass, it is verified that the flexible BEWOLED showed a similar or better electroluminescence (EL) performance.

Effect of broad recombination zone in multiple quantum well structures on lifetime and efficiency of blue organic light-emitting diodes

Blue phosphorescent organic light-emitting diodes with multiple quantum well (MQW) structures (from one to four quantum wells) within an emitting layer (EML) are fabricated with charge control layers (CCLs) to control carrier movement. The distributed recombination zone and balanced charge carrier injection within EML are achieved through the MQW structure with CCLs. Remarkably, the half-decay lifetime of a blue device with three quantum wells, measured at an initial luminance of 500 cd/m2, is 3.5 times longer than that using a conventional structure. Additionally, the device’s efficiency improved. These results are explained with the effects of triplet exciton confinement and triplet–triplet annihilation within each EML.

Blue Organic Light-Emitting Diodes Containing Anthracene Derivatives With End-Capping Phenyl Group

We have synthesized and characterized new blue host materials for OLEDs; 9,10-di-o-tolylanthracene (1), 2-tert-butyl-9,10-diphenylanthracene (2), 10,10′-diphenyl-9,9′-bianthracene (3), and 1,4-bis(10-phenylanthracen-9-yl)benzene (4). To explore electroluminescent properties of these materials, multilayered OLEDs with the configuration of ITO/NPB (50 nm)/Blue emitters (1–4) (30 nm)/Liq (2 nm)/Al (100 nm) were fabricated. Among those non-doped devices, the device 4a employing 4 as an emitter showed high efficiencies of 4.11 cd/A, 3.31 lm/W, and 2.35%, respectively. The device 2b employing 2 as host material for PFVtPh blue dopant material exhibited excellent efficiencies with 5.64 cd/A, 4.14 lm/W, and 4.54%.

Non-Doped Blue OLEDs Based on 9,9′-Dimethylfluorene Containing 10-Naphthylanthracene Derivatives

A series of blue fluorescent materials 1–3 based on 10-(2-napthyl)-anthracene derivatives with the diverse aromatic groups were synthesized and multilayer non-doped devices using them as emitting materials were fabricated. All OLED devices using these materials emit deep blue light of 446–456 nm. In particular, device 3 exhibited highly efficient blue emissions with the luminous efficiency of 3.89 cd/A, a power efficiency of 2.47 lm/W, Quantum Efficiency of 3.03% at 20 mA/cm2, and CIEx,y coordinates of (0.163, 0.149) at 6 V. Also, device 2 showed the efficient deep-blue emission with CIE coordinates of (x = 0.151, y = 0.104) at 6 V.

Soluble N-Type organic thin-film transistors with enhanced electrical characteristics

We fabricated and investigated soluble, organic, thin-film transistors (OTFTs) containing ‘[6, 6]-phenyl-C61-butyric acid methyl ester (PCBM)’ as a semiconducting layer, and an organic dielectric buffer (cross-linked poly-4-vinylphenol) as a dielectric buffer-layer to improve electrical characteristics. The semiconducting layer of the devices was fabricated by the drop-casting method where PCBM was dissolved in three different solvents (odichlorobenzene, chloroform, and chlorobenzene). From the transfer and output characteristics of the PCBM OTFTs, a threshold voltage of 10 V, sub-threshold slope of 10 V/dec, on/off current ratio of 7.305 × 103, and field-effect mobility of 1.53 × 10−2 cm2/Vs were obtained; for PCBM using o-dichlorobenzene solvent and an organic dielectric buffer layer. It was also found that the hysteresis for the same device was improved conspicuously compared to the other devices, by the above-mentioned condition.

Effect of electron transport layer engineering based on blue phosphorescent organic light-emitting diodes

Abstract A main requirement for achieving high efficiency in organic light-emitting diodes (OLEDs) is that all charges and electrically generated excitons should be employed for emission. We fabricated blue phosphorescent OLEDs with four types electron transporting layers, which were doped with lithium quinolate (Liq) from 0% to 10%. A series of blue devices consisted of indium tin oxide (ITO, 180xa0nm)/4,4-bis[N-(naphthyl)-N-phenyl-amino]biphenyl (NPB, 50xa0nm)/N,N′-dicarbazolyl-3,5-benzene (mCP, 10xa0nm)/iridium(III)bis[(4,6-di-fluoropheny)-pyridinato-N,C 2 ] picolinate (FIrpic) doped in mCP (8%, 30xa0nm)/1,3,5-tris(N-phenylbenzimidazole-2-yl)benzene (TPBi, 20xa0nm)/TPBi mixed with Liq (20xa0nm)/Liq (2xa0nm)/aluminum (Al, 100xa0nm). The blue OLED doped with 5% Liq, which demonstrated a maximum luminous efficiency and external quantum efficiency of 17.64xa0cd/A and 8.78%, respectively, were found to be superior to the other blue devices.

Two Anthracene-Containing Materials for Blue Organic Light-Emitting Diodes

We have designed and synthesized anthracene-benzene-anthracene containing blue emitters 1-3 end-capped with the various aryl groups using Suzuki cross coupling reaction. Multilayered OLEDs with the device structure of ITO/NPB (50 nm)/blue emitters (1-3) (40 nm)/Alq3 (15 nm)/Liq/Al were fabricated by using the compounds as blue emitting materials. All devices showed efficient blue emissions. Particularly, a highly efficient blue OLED was fabricated, showing the maximum luminance of 4674 cd/m2 at 9.5 V, the luminous efficiency of 1.95 cd/A, the power efficiency of 0.93 lm/W, the external quantum efficiency of 2.05% at 200 cd/m2 and CIEx,y coordinates of (0.163, 0.096) at 8.5V.