Efficiency enhancement of blue phosphorescent organic light-emitting diodes using mixed electron transport layer

•We fabricated blue PHOLED with mixed electron transport layer.•We investigated the electron transport mechanism according to different ETL materials.•The key features for improvement in PHOLEDs are triplet and LUMO energy levels of ETLs. Blue phosphorescent organic light-emitting diodes (OLED) using mixed electron transport layer (ETL) were fabricated with the device structure of ITO/NPB/mCP:Firpic-8%/TPBi:BCP or TPBi:3TPYMB/Liq/Al to observe mixed ETL’s influence on their electrical and optical characteristics. OLED device with mixed ETL of TPBi with BCP or 3TPYMB significantly improved its current efficiency to 30.4 and 34.2cd/A comparing to 19.8cd/A of single ETL with BCP only. We examined mixed ETL’s capability of electron transport and triplet exciton confinement enhancing phosphorescent OLED’s luminance and luminous efficiency.