Electrode Surface Treatment and Buffer Layer Deposition using RF Plasma for OLED

초록

Transparent indium-tin-oxide (ITO) electrode surface was modified using Ar/O3 plasma and organic layers were deposited on the ITO surface using 13.56 MHz RF plasma polymerization technique. We investigated effect of the RF plasma surface treatment and role of plasma polymerized buffer layer on the efficiency and lifetime of organic electroluminescence device (OLED). Poly styrene(PS), poly methymethacrylate (PMMA), poly vinylacetate (PVac) and poly acetylacetate (PAcac) layers were plasma polymerized on the ITO anode as buffer layer between anode and hole transfer layer (HTL). The plasma polymerization of the organic buffer layers were carried out at the home made capacitive-coupled RF plasma equipment. N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as HTL and tris(8-hydroxyquinoline)alunium (Alq3) as both emitting layer/electron transport layer (ETL) were deposited using thermal evaporation polymerization technique. Finally aluminum layer as cathode was vacuum evaporated. Fig.1 shows cross section of the OLEDs prepared in this study. Surface morphology/roughness and composition of the plasma treated ITO and buffer layers were investigated using atomic force microscope (AFM) and XPS/ESCA, respectively. For the purpose of investigating performance of the OLEDs, voltage-current-luminance characteristics of the samples with/without buffer layer and with RF treated/not treated ITO were measured using a source measurement unit and luminance meter. Effects of the plasma surface treatment of ITO and plasma polymerized buffer layers on the OLED performance were discussed.