Jung Joo Park

Highly efficient bilayer green phosphorescent organic light emitting devices

We present a highly efficient green phosphorescent device comprising only of two organic layers. A host material bis[2-(2-hydroxyphenyl)-pyridine]beryllium having a good electron transporting and energy transfer characteristics, and a wide band gap hole transport material N,N′-di(4-(N,N′-diphenyl-amino)phenyl)-N,N′-diphenylbenzidine lead to the fabrication of a simplified high efficiency device. The driving voltage value of 3.3V to reach a luminance of 1000cd∕m2 is reported. The maximum current- and power-efficiency values of 38.30cd∕A and 46.60lm∕W are demonstrated in this device. Results reveal a practical way to fabricate highly efficient truly bilayer organic devices for trouble-free manufacturing processes.

Spontaneous Patterning of Polymer Film by Teflon Thin Film and Spin Coating for Polymer Light-Emitting Diode

We have developed a selective coating technology for large-area polymer light-emitting devices (PLEDs). This can be done by using the different surface energy on the anode electrode. Teflon thin film can be used to make a hydrophobic surface (low surface energy) on the hydrophilic surface (high surface energy) of ITO for patterning of polymer film. Contact angle of ITO surface and Teflon coated one were 3 and 130°, respectively. In order to demonstrate PLED by spontaneous patterning of polymer film we have fabricated PLED consist of 4 and 8 elements in series on the same substrate. The voltage of the devices required to achieve a particular brightness scales approximately with the number of elements in series.

Self-Assembled Monolayer Modification of PEDOT:PSS Interface to Improve the Device Performance in Blue PLED

As a result of intensive research on polymer light-emitting diodes (PLEDs) for the last several years, the device performances have been remarkably improved. Recently, several researchers reported on a PLEDs with an interlayer between poly(3,4-ethylenedioxythiophene)-poly-(styrenesulfonate) (PEDOT:PSS) and an emissive polymer. It improved the device efficiency as well as the device lifetime. The role of the interlayer is to block the electron from back diffusion to PEDOT:PSS and/or to reduce luminescence quenching at the PEDOT:PSS interface. We studied the improvement of the PLED by inserting an octadecyltrichlorosilane (OTS) as the interlayer between PEDOT:PSS and the emissive layer. The OTS was treated on PEDOT:PSS through the self-assembled monolayer (SAM) process. It improved the device efficiency of the PLED from 3.86 to 4.76 cd/A, and increased the operation lifetime from 270 to 340 minute comparing the non-OTS treated PLED with the OTS treated PLED for 10 min. In blue PLED, inserting the OTS layer between blue polymer and PEDOT:PSS is promoted hole injection from an anode. Therefore, the device efficiency is improved, which appears to be due to the increase of balanced recombination as a result of the accumulated electrons near the interface between emissive layer and PEDOT:PSS.

White Polymeric Light-Emitting Diodes Based on Doping of an Orange Ir Complex in a Fluorene Blue Polymer Host

A series of white polymer light-emitting devices has been fabricated by using a spiropolyfluorene (SF) blue polymer with an orange Ir complex as a blend system. A SF single polymer host and mixed co-host with CBP (4,4-N,N-dicarbazolebiphenyl) or PBD (2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole) are investigated to get high efficiency white OLEDs. A good color coordination of (0.34, 0.36) with a good current efficiency of 1.52 cd/A at 2% doped condition in a CBP mixed co-host system is reported.

P-209: New Green Phosphorescent Host Materials

We report novel bipolar host materials for high efficiency green phosphorescent organic light emitting diode devices (PHOLEDs). Phenyl moieties were inserted in a 4,4′-N,N′-dicarbazolebipheyl (CBP) structure to reduce electron injection barrier and enhance electron mobility. The significant improvement of current and power efficiencies and reduction in turn-on voltage in green light-emitting PHOLEDs by this modification are observed. At a given constant luminance of 1000 cd/m2, current efficiency 53 cd/A, low driving voltage 6.5 V, and power efficiency 27 lm/W in 4,4′-N,N′-dicarbazoleterpheyl (CTP) host with Ir(ppy)3 dopant are reported. Results show better performance in green PHOLEDs with new host materials than CBP.

P-185: High Efficiency Solution Processed Red Phosphorescent OLEDs Based on a Soluble Small Molecule Host with an Ir(piq)3 Complex

We demonstrate that solution processed high efficiency and saturated red phosphorescent OLEDs can be achieved using a soluble small molecule (SSM) as the host material. Two structures of ITO /PEDOT /interlayer /SSM:Ir(piq)3 /LiF /Al and ITO /PEDOT /interlayer /SSM:Ir(piq)3 /sublimated Balq /sublimated Alq3 /LiF /Al were employed as all soluble processed devices and hybrid devices, respectively. A 6.36 cd/A of maximum luminance efficiency and a 3.22 lm/W of maximum power efficiency were obtained in a hybrid device. The CIE coordinate was (0.67, 0.33).