Fabrication and characterization of Al:ZnO transparent conducting oxides for application to organic light emitting devices

초록

Al doped ZnO (AZO) thin films were prepared by Nd:YAG pulsed laser deposition (PLD) and DC/RF magnetron sputtering technologies. In order to fabricate a low cost and low-temperature substrate compatible transparent conducting oxide (TCO) for flat panel display application, the Nd:YAG PLD and DC/RF magnetron sputtering process conditions were kept below 200C. For the both AZO preparation processes a 99.99% AZO target (Zn: 98 wt.%, Al2O3: 2 wt.%) was used. All the Nd:YAG pulsed laser deposited AZO thin films showed over 90% optical transmittance in visible region and electrical properties such as 4.6310-3 cm of electrical resistivity, 9.251020 cm-3 of carrier concentration, and 31.33 cm2/Vs carrier concentration. The AZO thin films prepared using DC/RF magnetron sputtering process showed over 85% optical transmittance in visible region and similar electrical properties to those of the Nd:YAG pulsed laser deposited samples. In order to verify feasibility of the AZO TCO thin films to organic light emitting device (OLED) application, test organic light emitting device was fabricated based on ITO or AZO as TCO, TPD as hole transporting layer (HTL), Alq3 as both emitting layer (EML) and electron transporting layer (ETL), and aluminium as cathode, where the both ITO and AZO surfaces were treated using O2 RF plasma with 100 W, 0.1 Torr for 3 min. The current-voltage-luminance (I-V-L) characteristics of the ITO/TPD/Alq3/Al and AZO/TPD/Alq3/Al OLEDs were evaluated using a source measurement unit (Keithley 2400) and luminance meter (TOPCON, BM-8). The performance of the OLEDs with AZO as transparent conducting anode was compared to those of the OLEDs with conventional ITO as transparent conducting anode.