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

Abstract

Abstract 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 ( Alq 3 ). 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 Alq 3 , 30 and 15 nm, respectively, emitted strong electroluminescence (EL) as intense as 25,000 cd/m 2 . For practical solid state lighting application, EL intensity exceeding 1000 cd/m 2 was achieved at current density of 18–19 mA/cm 2 or driving voltage of 6.5–8 V and the devices exhibited external quantum efficiency ( η ext ) of 2.6–2.9% corresponding to power efficiency ( η P ) of 2.1–2.3 lm/W at the required brightness. The thickness of Alq 3 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 (CIE x , y = 0.34, 0.31) along with higher CRI of 83 at 8 V, although higher voltage deteriorated the color quality of WOLED.