Byoung-Sang Kim

Electron Transport Properties of Zn(phen)q Compared with Alq3 in OLED

We synthesized new electroluminescence materials [(1,10-phenanthroline)(8-hydroxyquinoline)] Zn(phen)q and investigated their electron transport properties. We used Zn(phen)q and Alq3 for the conductive materials and measured their electron transport properties as a function of the organic layer thickness. The difference between Zn(phen)q and Alq3 as electron transporting materials suggests that the electrical properties depends on the carrier injection.

Efficiency Improvement of OLED by Aquaregia and RCA Treatment of ITO Substrate

Indium tin oxide (ITO) is widely used as the anode material in organic light-emitting diodes (OLEDs) because of its good electrical transport, optical transparency, high work function, and efficient hole-injection properties. Surface treatments have an effect on ITO parameters such as the work function, surface roughness, carrier concentration, mobility, and surface sheet resistance, so that with appropriate surface treatment significant improvement in the OLED performance can be achieved. In this work, we investigated the effect of aquaregia (HNO3, HCl, distilled-water = 1:3:20) and RCA (company name, NH4OH, H2O2 distilled-water = 1:4:20) cleaning treatments of this interface on OLED performance. The layers used in the OLED were ITO/NPB/Alq3/LiF/Al. The characteristics of the OLEDs current density-voltage-luminance, and efficiency were measured. We found that the aquaregia and RCA treatments enhanced the performance of the OLED. For the ITO treatments, the maximum luminance and efficiency were increased by a factor of ∼2 relative to the untreated device. Subsequent enhancement of performance of the diodes was obtained with treated ITO substrates, proving the effectiveness of the treatments. The mechanism of ITO treatment was investigated by analyzing the contact angle of water droplets on the surface.

Electron Transporting Layer Effect of OLED Using Zn(HPQ)2

We have synthesized (8-hydroxy-7-propylquinoline) zinc(II) (Zn(HPQ)2) to use in OLED. Photoluminescence (PL) peak of Zn(HPQ)2 was observed at 555 nm which showed yellow emission. In the cyclic voltammetry (CV) experiment, the HOMO and the LUMO of the Zn(HPQ)2 measured to be 6.7 eV and 3.3 eV. So we expected that Zn(HPQ)2 could be used as emitting layer (EML) and electron transporting layer (ETL). In this study, we investigated the efficiency properties of OLED based on Zn(HPQ)2 as ETL. The device structures were ITO/NPB/Alq3/Zn(HPQ)2/LiF/Al. Prior to film deposition, ITO substrate performed surface treatment by UV-ozone for 1 minute. We fabricated devices by thickness change of Zn(HPQ)2, so we founded optimal condition about thickness. Improvement of the OLED performance can be attributed to the reduction of the electron injection barrier of the Zn(HPQ)2 layer.

Photoluminescence and Electroluminescence Characteristics of Benzoxazole Dendrimers

Various studies have been done using dendrimers as emissive materials for OLEDs, although efficiencies are still significantly lower than those offered by evaporated devices. In this study, dendrimers were synthesized. Photoluminescence (PL) and Electroluminescence (EL) characteristics of Benzoxazole dendrimers were investigated by fabricating the device of structure such as ITO/PVK: Benzoxazole dendrimers: PBD/Li:Al. We used PVK as hole transport material and blended with PBD as electron transport material. The Benzoxazole dendrimers studied here used emissive material. The PL spectra of 1st generation and 2nd generation Benzoxazole dendrimers show blue emission at 438 nm. The EL spectra of 1st generation and 2nd generation Benzoxazole dendrimers were observed at the wavelength of 441 nm and 447 nm.

Efficiency properties of OLED based on Zn(PQ) 2 as electron transporting layer and hole blocking layer

We have synthesized 8-hydroxy-7-propylquinoline (Zn(PQ)2) to use in OLED. Photoluminescence (PL) peak of Zn(PQ)2 was observed at 555 nm which showed yellow emission. In the cyclic voltammetry (CV) experiment, the HOMO and the LUMO of the Zn(PQ)2 measured to be 6.7 eV and 3.3 eV. So we expected that Zn(PQ)2 could be used as electron transporting layer (ETL) and hole blocking layer (HBL). In this study, we investigated the efficiency properties of OLED based on Zn(PQ)2 as ETL and HBL. Prior to film deposition, ITO substrate performed surface treatment by UV-ozone for 1 minute. Improvement of the OLED performance can be attributed to the reduction of the electron injection barrier of the Zn(PQ)2 layer.

Improvement of efficiency for OLED using Zn(HPB)q as electron transporting layer

We synthesized a new material, (2-(2-hydroxy phenyl)benzo xazole)(8-hydoxyquinoline) [(Zn(HPB)q] which has low molecular compound and studied the improvement of OLED using Zn(HPB)q. The PL spectrum of Zn(HPB)q was yellowish green at a wavelength of 532 nm. Through cyclic-voltammetry, the ionization potential (IP) and the electron affinity (EA) were found to be 6.8 eV and 3.5 eV, respectively. We observed the possibility of Zn(HPB)q as electron transporting layer (ETL). Zn(HPB)q has been investigated as an ETL in the OLED and the optimal thickness of the Zn(HPB)q layer is about 10nm. We have obtained an improvement of luminance and decrease of turn-on voltage using Zn(HPB)q as ETL.