Organic light-emitting diode lighting with high out-coupling and reliability: Application of transparent amorphous ZnO–SiO2 semiconductor thick film

Abstract

Abstract We report that combination of high refractive index scattering layer made of glass and very thick amorphous ZnO-SiO2 (a-ZSO) semiconductor film is a route for obtaining both high out-coupling and reliability. a-ZSO is a promising material for electron injection/transport layer (EIL/ETL) in OLEDs; it has exceptionally small work function of ∼3.5 eV and high electron mobility of ∼1cm2/(Vs) (conductivity = 3.4 × 10−4 Scm−1), and can form ohmic contact with ITO. Thus, very thick a-ZSO film is applicable for EIL/ETL with no increase in turn-on voltage. Furthermore, a-ZSO has high transparency in the visible light region and a good index matching with the high index scattering layer, which is the most critical criterion to keep high out-coupling efficiency. Consequently, we succeeded in fabricating very stable and efficient OLED using 245 nm thick a-ZSO with the scattering layer which indicates ∼1.7 times higher out-coupling efficiency and smaller leakage current than the OLED with conventional glass substrate and a-ZSO thin film. This technology will be efficient for practical OLED lighting, and the durability against short circuit is also expected to improve.