Aging of ITO anodes treated by supercritical CO2/H2O2 fluids for OLEDs

Abstract

The aging behaviors of indium tin oxide (ITO) anodes treated by supercritical CO2/H2O2 (SCCO2/H2O2) fluids were investigated. As the SCCO2/H2O2-treated ITO anodes were aged, the contact angle and surface energy were analyzed and compared with those of the ITO anodes treated by oxygen plasma. The SCCO2/H2O2 pretreatment yielded a stable polar component of the ITO surfaces after 48 h of aging. The energy reduction in the polar component of the oxygen-plasma-treated ITO due to aging was 20 %, as compared with the 1.1 % decrease in ITO treated with the SCCO2/H2O2 fluids at 4000 psi for 15 min. The X-ray photoelectron spectroscopy analysis revealed that the oxygen content of the ITO surfaces with the SCCO2/H2O2 pretreatment was significantly higher than that of the ITO treated by oxygen plasma. This could result from the formation of hydroxyl products that functioned as a stable buffer layer against further contamination during aging. In addition, the correlated dependence of the OLED performance on the aged ITO anodes was also studied. The OLEDs with the SCCO2/H2O2 pretreatment showed an improved degradation of I–V characteristics and brightness in comparison with those of the devices treated with oxygen plasma after aging the treated ITO anodes for 6 and 12 h. The obtained results suggested that the ITO anodes treated by the SCCO2/H2O2 fluids exhibited a stable surface chemistry and could be useful for OLED applications.