Improved chromaticity and electron injection in a blue organic light-emitting device by using a dual electron-transport layer with hole-blocking function

A dual electron-transport layer (d-ETL) with hole-blocking function was successfully applied to a 2-(t-butyl)-9,10-di(2-naphthyl)anthracene (TBADN)-based blue organic light-emitting device (OLED) for improving chromaticity and electron injection. The d-ETL was constructed by sandwiching a 1,3-bis[2-(2,2'-bipyridin-6-yl)-1,3,4-oxadiazol-5-yl]benzene (Bpy-OXD) layer between the emission layer (EML) and the most common ETLs of tris(8-hydroquinoline) aluminum (Alq3) and 4,7-diphyenyl-1,10-phenanthroline (BPhen). Due to the hole-blocking function of Bpy-OXD and thereby the better confinement of carriers within the EML, d-ETL devices showed much better chromaticity and less current-induced color shift as compared to the corresponding single ETL ones. Moreover, the d-ETL devices revealed higher power efficiency (increased by ~30%) and lower driving voltage, indicating an enhanced electron injection. This could be explained by the fact that an interlayer of Bpy-OXD provided a stepped energy level which greatly facilitated electron injection and hence enhanced injection current.