We have investigated performance of green and blue phosphorescent organic light-emitting diodes (OLEDs) with red dye doped hole transport layers (HTLs). We utilize three different materials of N,N'-bis(naphthalen-1-yl)-N,N'-bis(phenyl)-2,2'-dimethylbenzidine (a-NPD), 3,6-bis-biphenyl-4-yl-9-[1,1',4',1?]terphenyl-4-yl-9H-carbazole (BBTC), and 4,4'-N,N'-dicarbazole-biphenyl (CBP) for the HTL and bis(1-phenylisoquinoline) (acetylacetonate)iridium(III)  ((piq)2Ir(acac)) is used as a red dye. The a-NPD, BBTC, and CBP have different highest-occupied-molecular-orbital (HOMO) energy levels and the HOMO energy level difference between the HTL and the red dye affects the performance of devices when the red dye is doped in HTLs. We have fabricated green and blue phosphorescent OLEDs with the red dye doped HTLs as well as undoped HTL. The driving voltages of devices with the red dye doped the HTLs are similar or slightly higher compared with those of the devices with the undoped HTL which might be explained by HOMO energy level differences, but the efficiencies and the colors of the devices are rarely changed regardless of the insertion of the red dye doped HTL. The change of the device characteristics is getting less as the difference of HOMO energy level between HTLs and the red dye is lower. As the OLED with the red dye doped HTL and without the blue and the green emission layers shows red emission, it can be used a common HTL in full color OLED panels. By using this layer, we can reduce one fine metal mask process for a red pixel patterning in the full-color OLED display.

Device characteristics of green and blue phosphorescent organic light-emitting diodes with red dye doped hole transport layers

248th National Meeting (2014)

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