Organic white light-emitting diodes using a new DCM derivative as an orange-red doping molecule

Abstract

A new DCM derivative containing a phenothiazine moiety, 4-(dicyanomethylene)-2- t-butyl-6 -(9-ethylphenothiazine-2-enyl) -4 H-pyran (DCPTZ), has been synthesized for use as an orange-red fluorescent dye molecule in organic light-emitting diodes (OLEDs). EL devices with the structure ITO/PEDOT-PSS/α-NPD/Alq 3:DCPTZ/Alq 3/LiF/Al were fabricated with various DCPTZ doping concentrations. The maxima in the EL spectra of the devices varied from 580 to 620 nm depending on the doping concentration of the dye molecule. An EL device with 0.5% dopant concentration was found to exhibit a maximum brightness of 81,500 cd/m 2 at 13.3 V and a power efficiency of 4.1 lm/W with CIE coordinates (0.51, 0.47) at a luminance of 100 cd/m 2. White light-emitting devices with the structure ITO/PEDOT-PSS/α-NPD/α-NPD:DCPTZ/DPVBi/Alq 3/LiF/Al were also fabricated. The thickness of the blue light-emitting 1,4-bis(2,2-diphenylvinyl)benzene (DPVBi) layer was varied to obtain white light emission. White light emission from the device was observed when the thickness of the DPVBi layer was greater than 10 nm. The maximum brightness and power efficiency of the device with a 20-nm DPVBi layer were found to be 30,300 cd/m 2 and 2.0 lm/W, respectively, with CIE coordinates (0.33, 0.36). In addition, the white EL device exhibits a relatively high color rendering index (CRI) of about 83.