White organic electroluminescence from fluorescent bis (2-(2-hydroxyphenyl) benzoxazolate)zinc doped with phosphorescent material

Efficient white electroluminescence has been obtained by using an electroluminescent layer comprising of a blue fluorescent his (2-(2-hydroxyphenyl) benzoxazolate)zinc [Zn(hpb)(2)] doped with red phosphorescent bis (2-(2'-benzothienyl) pyridinato-N,C-3')iridium(acetylacetonate) [Ir(btp)(2)acac] molecules. The color coordinates of the white emission spectrum was controlled by optimizing the concentration of red dopant in the blue fluorescent emissive layer. Organic light-emitting diodes were fabricated in the configuration ITO/alpha-NPD/Zn(hpb)(2):0.01 wt%Ir(btp)(2)acac/BCP/Alq(3)/LiF/Al. The J-V-L characteristic of the device shows a turn on voltage of 5 V. The electroluminescence (EL) spectra of the device cover a wide range of visible region of the electromagnetic spectrum with three peaks around 450, 485 and 610 nm. A maximum white luminance of 3500 cd/m(2) with CIE coordinates of (x, y = 0.34, 0.27) at 15 V has been achieved. The maximum current efficiency and power efficiency of the device was 5.2 cd/A and 1.43 Im/W respectively at 11.5 V. (C) 2009 Elsevier B.V. All rights reserved.