Efficient hole injection in blue organic light-emitting devices by using a double hole injection layer to improve chromaticity and electrical characteristics

A double hole injection layer consisting of Ag2O//MoOx was applied to a 4,40-bis (2,2-diphenylvinyl)-1,10-biphenyl-based blue organic light-emitting device (OLED). The hole current injection of the device was improved and the performance of the blue OLED was enhanced. We have observed that the insertion of such double layer leads to a striking improvement in chromaticity and electrical characteristics. This device showed much better chromaticity and less current-induced color shift as compared to the corresponding single hole injection layer counterparts. Using this strategy, a striking improvement in the electrical properties with lower driving voltage, higher power efficiency and a weak current-induced fluorescence quenching was achieved. This could be explained by the fact that an interlayer of Ag2O//MoOx provided a stepped energy level which greatly facilitated hole injection and hence enhanced injection current. The result is verified by using the J–V curves of ‘only’ devices and further explained with the help of Fowler-Nordheim (F-N) tunneling theory.