New type of White-Light Emitting Diode (WOLED) that emits three primary colors of red, green and blue has been demonstrated. WOLED is properly laid out with emitting layers so that all three wavelengths of light can be emitted by using fit energy level, and the organic functional layer named white balanced layer (WBL) is introduced. As for the material used as WBL, the experiment used NPB that has electron blocking effect with its large LUMO value. The color purity of such WOLED can be easily adjusted through the adjustment of the number of electron carriers injected into light emitting layer. In this of study, color coordinate was (0.341, 0.424) and light emitting efficiency was 16.5 cd/A at current density 10 mA/cm2, so the WOLED demonstrated highly efficient characteristics of over commercial level.

Two different emitting compounds, 1-[1,1;3,1]Terphenyl-5-yl-6-(10-[1,1;3,1]terphenyl-5-ylanthracen-9-yl)-pyrene (TP-AP-TP) and Poly-phenylene vinylene derivative (PDY 132) were used to white OLED device. By incorporating adjacent blue and yellow emitting layers in a multi-layered structure, highly efficient white emission has been attained. The device was fabricated with a hybrid configuration structure: ITO/PEDOT (40 nm)/PDY-132 (8∼50 nm)/NPB (10 nm)/TP-AP-TP (30 nm)/Alq3 (20 nm)/LiF (1 nm)/Al (200 nm). After fixing TP-AP-TP thickness of 30 nm by evaporation, PDY-132 thickness varied with 8, 15, 35, and 50 nm by spin coating in device. The luminance efficiency of the white devices at 10 mA/cm2 were 2.93 cd/A∼6.55 cd/A. One of white devices showed 6.55 cd/A and white color of (0.290, 0.331).

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.

본 논문에서는 청색 인광 발광 물질인 bis(3,5-Difluoro-2-(2-pyridyl)phenyl-(2-carboxypyridyl) iridium (III) (Flrpic)과 녹색 인광 발광 물질인 fac-tris(2-phenypyridine) irdium(III) (Ir(ppy)3)와 적색 인광 발광 물질인 his(5-benzoyl-2-phenylpyridinato-C,N)iridium(III) (acetylacetonate) ((Bzppy)2Ir(acac))를 각각 적층하여 백색 유기 발광 다이오드를 제작하였고, 각각의 발광층 사이에 혼합된 스페이서인 4,4'-N,N'-dicarbazole-biphenyl (CBP):4,7-diphenyl-1,10-phenanthroline (BPhen)을 적층하여 그 때의 영향에 대하여 연구하였다. 최적화된 구조에서의 전력 효율은 0.014 mA/cm2에서의 19.7 lm/w를 나타내었으며, 0.127 mA/cm2에서의 11.5%의 외부 양자 효율을 나타내었고, 8 V에서 Commission Internationale do I'Eclairage (CIEx,y) coordinates (x=0.36, y=0.44)의 색좌표를 나타내었다.