Blue organic light-emitting diodes with low driving voltage and enhanced power efficiency based on MoO3 as hole injection layer and optimized charge balance

In this letter, blue organic light-emitting diodes (OLEDs) with a different hole injection layer (MoO3 or m-MTDATA), and a different electron transport layer (Alq3 or BPhen) have been investigated. With 9,10-bis(2-naphthyl)-2-t-butylanthracene (TBADN) doped with (3 wt.%) P-bis(P-N,N-diphenyl-aminostyryl)benzene (DSA-Ph) as an emitting layer, the typical device structure is ITO/HIL (5 nm)/NPB (25 nm)/EML (35 nm)/ETL (15 nm)/LiF (0.8 nm)/Al (100 nm). It has been found that MoO3//BPhen based device shows the lowest driving voltage and highest power efficiency among the referenced devices. At the current density of 20 mA/cm2, its driving voltage and power efficiency is 5.2 V and 4.2 lm/W, which is independently reduced 48% and improved 44% compared with those of the m-MTDATA//Alq3 based one, respectively. The energy level diagram of the devices and single-carrier devices are studied to explain the reasons behind this improvement. The results strongly indicate that carrier injection ability and balance shows significant affects on the performance of OLED.