Efficient polymer white-light-emitting devices based on two complementary phosphorescent colors

Abstract

White polymer light-emitting diodes (WPLEDs) were fabricated by spin coating method using two complementary colors. The device structure used here is ITO/PEDOT (40 nm)/emitting layer (80 nm)/Ba (4 nm)/Al (120 nm). When the mass ratio of PVK:OXD-7:iridium bis(2-(4,6-difluorophenyl)-pyridinato-N,C2)picolinate (Firpic):tris(3-(2,6-dimethylphenoxy)-6-(thiophen-2-yl)pyridazine)iridium (Fs-1) was 63:27:10:0.25, white light with Commission Internationale de L'Eclairage (CIE) coordinates of (0.30, 0.39) was obtained. The maximum current efficiency was 10.8 cd· A-1 and the maximum brightness was 4200 cd· m-2. To improve the hole-electron injection balance and the device's character, a thin layer of water-soluble electronic transporting material was used to modify the cathode. In this case, efficient white light emission with a maximum current efficiency of 13.1 cd· A-1 and a maximum brightness of 6069 cd· m-2 was obtained. Using poly[(9,9-bis(3'-(N,N-dimethylamino) propyl)-2,7-fuorene)-alt-2,7-(9,9- dioctylfuorene)] (PFN) (20 nm)/Al (120 nm) as the cathode resulted in CIE coordinates of (0.33, 0.39) and the EL spectrum was also found to be quite stable. The effects of charge trapping and energy transfer on device performance were discussed by considering the photoluminescence (PL) and electroluminescence (EL) spectra as well as the energy.