Organic light-emitting diodes fabricated on a new transparent conducting anode: aluminium-doped zinc oxide

Abstract

Transparent conducting oxides (TCO) such as indium oxide (In2O3), zinc oxide (ZnO) and doped oxides have been intensively investigated for many years. Among all of the TCO films, tin-doped indium oxide (ITO) is the most extensively used material for display industry such as liquid crystal, plasma and organic electroluminescence displays. However, there are some disadvantages of ITO. Indium is a rare element and is expensive. Besides, it is chemically instable in reducing ambient. Moreover, the toxic nature of indium is believed to be harmful to human and environment. To achieve optimal device performance and reduce production cost, it is necessary to seek new electrode materials. Recently, impurity-doped zinc oxide (ZnO) film has been intensively investigated as an alternative choice of replacing ITO films. Zinc oxide is an abundant, inexpensive and non-toxic material. It is also chemically stable under hydrogen plasma processes that are commonly used for the fabrication of solar cell [1]. The doping of ZnO with aluminium can increase the conductivity of the films as it is the best dopant [2]. In this project, a new approach of fabrication of AZO deposited on glass and PET substrate by radio frequency magnetron sputtering was attempted. We investigated that OLED made with this anode on PET had a satisfactory resistance of 7.5×10-4 ohm-cm to that of ITO on PET which were 5.23×10-4 ohm-cm. Moreover, the optical transmittance of both AZO and ITO films were very high which were over 85%. So, they are very good at transparent OLED devices fabrication. Furthermore, the current efficiency of AZO on PET device was about 3.6 cd/A. For comparison purpose, ITO on PET device was also fabricated. The efficiency of this device was 4.1 cd/A. The results suggested that optimized AZO films can severe as an alternate anode material to ITO for OLED application.