Korean Journal of Materials Research ISSN:1225-0562(Print) 2287-7258(Online) 한국재료학회지

White organic light-emitting diodes with a structure of indium-tin-oxide [ITO]/ N,N-diphenyl-N,N-bis-[4-(phenylm-tolvlamino)-phenyl]-biphenyl-4,4-diamine [DNTPD]/ [2,3-f:2, 2-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile [HATCN]/ 1,1-bis(di-4-poly-aminophenyl) cyclo -hexane [TAPC]/ emission layers doped with three color dopants/ 4,7-diphenyl-1,10-phenanthroline [Bphen]/ Cs₂CO₃/ Al were fabricated and evaluated. In the emission layer [EML], N,N-dicarbazolyl-3,5-benzene [mCP] was used as a single host and bis(2-phenyl quinolinato)-acetylacetonate iridium(III) [Ir(pq)₂acac]/ fac-tris(2- phenylpyridinato) iridium(III) [Ir(ppy)₃]/ iridium(III) bis[(4,6-di-fluoropheny)-pyridinato-N,C2] picolinate [FIrpic] were used as red/green/blue dopants, respectively. The fabricated devices were divided into five types (D1, D2, D3, D4, D5) according to the structure of the emission layer. The electroluminescence spectra showed three peak emissions at the wavelengths of blue (472~473 nm), green (495~500 nm), and red (589~595 nm). Among the fabricated devices, the device of D1 doped in a mixed fashion with a single emission layer showed the highest values of luminance and quantum efficiency at the given voltage. However, the emission color of D1 was not pure white but orange, with Commission Internationale de L’Eclairage [CIE] coordinates of (x = 0.41~0.45, y = 0.41) depending on the applied voltages. On the other hand, device D5, with a double emission layer of mCP:[Ir(pq)₂acac(3%) +Ir(ppy)₃(0.5%)]/ mCP:[FIrpic(10%)], showed a nearly pure white color with CIE coordinates of (x = 0.34~0.35, y = 0.35~0.37) under applied voltage in the range of 6~10 V. The luminance and quantum efficiency of D5 were 17,160 cd/m² and 3.8% at 10 V, respectively.