Low-power-consumption and long-lifetime OLED with a high Tg n-type organic transport material

In this paper, we demonstrated an organic light emitting device (OLED) of low driving voltage, high current efficiency and long lifetime by using an n-type organic material as the electron transport layer (ETL). Such a layer is composed of a large alkali metal, i.e. Cesium (Cs), doped into the organic material. Cs atom is heavy and hard to diffuse into the emitting layer (EML) material that decreases the metal quenching and increase the operation lifetime. 2,9-dimethyl-4,7-diphenyl 1,10- phenanthrolin (BCP) and 2,5-diaryl-1,3,4-oxadiazoles (OXD) were used as the host organic material. OXD is thermally stable and exhibits a high glass transition temperature (Tg) of 147°C that can further increase the operation lifetime. The resistivity of those doped materials is about 3x105 Ω-cm that is two orders of magnitude lower than the resistivity of the pure organic materials. Compared with the conventional LiF/Al device, about two-volt reduction in driving voltage was observed. Current efficiency is also increased due to better carrier balance. Operation lifetimes of metal dopant devices are longer than that of the conventional device especially by using OXD as the host of the ETL.