Efficient white light emitting devices with a blue emitting layer doped with a red dye

Abstract

We report the fabrication and the characterization of white organic light emitting devices consisting of a single light emitting layer of blue-emitting bis(2-methyl-8-quinolinolato) (triphenyl-siloxy)aluminium (III) (SAlq) doped with red-emitting 4-dicyanomethylene-2-methyl-6-[2-(2,3,6,7-tetrahydro-1H,5H-benzo[i,j]quinolizin-8-yl)vinyl]-4H-pyran) (DCM2). White light emission can be obtained from the incomplete energy transfer from SAlq to DCM2 and the direct trapping of carriers at DCM2. The electroluminescence (EL) spectrum consists of two broad peaks around 480 and 570 nm, resulting in white light emission with the CIE coordinates (0.32, 0.38). The introduction of the PEDOT–PSS buffer layer leads to an increase in the current density and the luminance by a factor 6 under the forward bias. The device with PEDOT–PSS shows an EL turn-on voltage of about 3 V and the maximum luminance of 18,100 cd/m2 at the bias of 13.2 V. The luminous efficiency is about 2.1 lm/W and the external quantum efficiency is 1.9% at a luminance of 100 cd/m2.