White Electroluminescence Obtained from a Polymer Light-Emitting Diode Containing Two Phosphorescent Iridium (III) Complexes in an Emitting Layer

Abstract

Aimed at fabrication of a soln.-processed white polymer light-emitting diode, novel phosphorescent bis-cyclometalated Ir III complexes were developed; bis [2- 3,5-bis trifluoromethyl Ph pyridinato-N,C2'] iridium III (2,2,6,6-tetramethylheptane-3,5-dionate-O,O) #1 and bis [2-(dibenzo [b,d] furan-4-yl) quinolinato-N,C3] iridium III [1,3-bis(3,4-dibutoxyphenyl)propane-1,3-dionate-O,O] #2. The complex 1 exhibited bluish-green photoluminescence (PL) at 475 and 507 nm with a quantum yield (ϕPL) of 0.91 (toluene, rt), and 2 showed red PL at 610 nm with ΦPL of 0.77 (toluene, rt). Using these phosphorescent complexes, PVCz-based PLEDs were fabricated (PVCz; poly(N-vinylcarbazole)), of which structures were ITO (150 nm)/PEDOT:PSS (40 nm)/PVCz : PBD : 1 (or 2) (100nm)/CsF (1.0nm)/Al (250 nm). The PLEDs contg. 1 and 2 exhibited bluish-green and red electroluminescence (EL), resp., in similar regions to their PL. These results indicated that the combination of these complexes as co-dopants should yield white luminescence. Indeed, the PLED contg. both of 1 and 2 in a PVCz emitting layer was fabricated. When the ratio of PVCz : PBD : 1 : 2 was adjusted to 10 : 3.0 : 1.2 : 0.012 (wt/wt/wt/wt), white EL with a CIE chromaticity coordinate of (0.364, 0.378) was obtained with max. luminance of 4200 cd m-2 at 13.0 V, affording max. current efficiency of 4.9 cd A-1 at 7.0 V, max. power efficiency of 2.4 lm W-1 at 6.0 V, and max. external quantum efficiency of 2.4% at 7.0 V. [on SciFinder(R)]