RESUMEN
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.
RESUMEN
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.
RESUMEN
An effect of bilayer cathode Li2O/Al system was studied in Alq3 based organic light-emitting diodes with a variation of Li2O layer thickness from 0 to 10 nm. The device was made in a structure of ITO/(TPD)/Alq3/Li2O/Al. Current density-luminance-voltage (J-L-V) characteristics and a built-in voltage of the device were measured at ambient conditions. Built-in voltage in the device is generated due to a difference of work functions between the anode and cathode. From the J-L-V characteristics of the device, we observed an increase in luminance and current efficiency by more than 100 times and 2 times, respectively, for the device with 0.5 nm thick Li2O layer. The measured built-in voltage shows that the device with 0.5 nm thick Li2O layer has relatively higher built-in voltage compared to the others. Since the higher value of built-in voltage corresponds to the lower value of electron barrier height in cathode, the improvement in the efficiency for the device with 0.5 nm thick Li2O layer is thought to be due to a lowering of the electron barrier height.
RESUMEN
An effect of bilayer cathode Li20/Al was studied in Alq3 based organic light-emitting diodes with a variation of Li2O layer thickness. The current-luminance-voltage characteristics of ITO/TPD/Alq3/Li2O/Al device were measured at ambient condition to investigate the effect of Li2O/Al. It was found that when the thickness of Li2O layer is in the range of 0.5-1 nm, there are improvements in luminance, efficiency, and turn-on voltage of the device. A current density and a luminance are increased by about 100 times, a turn-on voltage is lowered from 6 V to 3 V, a maximum current efficiency is improved by a factor of 2.3, and a maximum power efficiency is improved by a factor of 3.2 for a device with a use of thin Li2O layer compared to those of the one without the Li2Otron-barrier height for electron injection from the cathode to the emissive layer.