O2 Plasma Treatment of ITO Substrates for Improvement of Organic Electroluminescence Device Performance

초록

We investigated the effect of O2 plasma treatment of indium-tin-oxide (ITO) surface on the performance of organic electroluminescence devices (OLEDs). The OLED had a structure of ITO/N,N'-diphenyl-N,N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine(TPD)/tris(8-hydroxyquinoline)aluminum(Alq3)/Al. The ITO(Samsung Corning, 20ohm/square) layer was patterned into a stripe width of 2 nm. The capacitive-coupled plasma equipment was used for plasma surface treatment. 13.35 MHz RF plasma generator(AUTO ELEC. ST-500) with a matching box was connected to the ring electrodes. O2 plasma treatment was carried out at the pressure of 0.1 torr and the RF power of 100 W. Fig.1 shows a schematic of the plasma equipment. ITO surface treated O2 plasma has been analyzed using atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). It was found that the surface carbon contaminations were completely removed by the O2 plasma treatment and that the surface atomic concentations were changed. It was also shown that the O2 plasma treatment of ITO anode improves the stability of the OLEDs due to the modification of the surface states. The active area of the devices was 4mm2. Voltage, current, and luminescence were measured at the same time. The characteristics of current density and luminance according to the applied voltage change were measured by a source measurement unit (SMU: Keithley, Model 2400) and luminace meter (TOPCON, BM-8). Fig.2 shows luminance-current density characteristics. The luminance of the OLEDs was measured with the use of the O2 plasma treated ITO substrates.