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

摘要

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 fluo-rophore 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 14V. Device B exhibited relatively high color rendering indexes (CRTs) 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.