Enhancing Color Purity and Efficiency of White Organic Light-Emitting Diodes Using an Extinction Layer

A highly efficient double-doped white organic light-emitting diode (WOLED) was prepared and characterized. The double-doped emissive layer consists of a host material, 4,4(')-bis(carbazol-9-yl)-biphenyl, doped with 8 wt % blue electrophosphorescent sensitizer, bis[(4,6-difluorophenyl)-pyri-dinato-N,C-2'] (picolinato) Ir(III), and 0.6 wt % fluorescent dye, (2-methyl-6-[2,3,6,7-tetrahydro-1H,5H-benzo[ij]quinolizin-9-yl)ethenyl]-4H-pyran-4-ylidene] propane-dinitrile. The WOLED can exhibit the maximum luminous efficiency of 16.2 cd/A and the luminance of 17,800 cd/m(2). Electroluminescence spectra reveal that the corresponding Commission Internationale de L'Eclairage coordinates of the WOLED are x=0.36 and y=0.39. Furthermore, inserting copper phthalocyanine (CuPC) as an extinction layer between 4,4('),4(')-tris(N-3-methylphenyl-N-phenyl-amino)-triphenylamine and indium tin oxide in WOLED could effectively restrain the red emission of the electroluminescent spectra and give colors close to the equal-energy white (0.33, 0.33).