High-efficiency two-colour white organic light-emitting diodes (WOLEDs) comprising a newly synthesized iridium complex orange phosphor ((impy) 2Ir(acac)) and a blue fluorophor (BD012) have been realized by placing several kinds of thin spacers between two emitters. Hybrid WOLEDs with a spacer composed of a hole-transporting N, N-dicarbazolyl-3,5-benzene (mCP) and an electron-transporting 4,7-diphenyl-1,10-phenanthroline (Bphen) exhibit a high external quantum efficiency (EQE) of up to 8.4% and a negligible colour change (the colour coordinate of (0.39, 0.41) at 1000 cdm-2) with increasing brightness, whereas the device using a hole-transporting mCP spacer shows a relatively low EQE of 6.2% and a large shift of emitting colour with increasing brightness. Device performance is further characterized based on the charge transport behaviour of the spacers inserted between the two emitters.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Acoustics and Ultrasonics
- Surfaces, Coatings and Films