All non-dopant red–green–blue composing white organic light-emitting diodes

All non-dopant white organic light-emitting diodes (WOLEDs) have been realized by using solid state highly fluorescent red bis(4-(N-(1-naphthyl)phenylamino)phenyl)fumaronitrile (NPAFN) and amorphous bipolar blue light-emitting 2-(4-diphenylamino)phenyl-5-(4-triphenylsilyl)phenyl-1,3,4-oxadiazole (TPAOXD), together with well known green fluorophore tris(8-hydroxyquinolinato)aluminum (Alq3). The fabrication of multilayer WOLEDs did not involve the hard-to-control doping process. Two WOLEDs, Device B and C, different in layer thickness of Alq3, 30 and 15 nm, respectively, emitted strong electroluminescence (EL) as intense as 25,000 cd/m2. For practical solid state lighting application, EL intensity exceeding 1000 cd/m2 was achieved at current density of 18–19 mA/cm2 or driving voltage of 6.5–8 V and the devices exhibited external quantum efficiency (ηext) of 2.6–2.9% corresponding to power efficiency (ηP) of 2.1–2.3 lm/W at the required brightness. The thickness of Alq3 layer is decisive in color quality of non-dopant WOLEDs. The Commission Internationale de l’Eclairage (CIE) coordinates of fairly white EL of Device B varied only little from (0.34, 0.39) to (0.34, 0.38) at driving voltage between 6 and 14 V. Device B exhibited relatively high color rendering indexes (CRIs) in the range of 74–81, which were essentially voltage-independent. The other WOLED, Device C, showed even better color purity of white EL (CIEx,y = 0.34, 0.31) along with higher CRI of 83 at 8 V, although higher voltage deteriorated the color quality of WOLED.