Organic light-emitting diodes with F16CuPC as an efficient hole injection layer

Abstract

We report a new hole-injection material, copper hexadecafluorophthalocyanine (F$_{16}$CuPC) for organic light-emitting diodes (OLEDs) consisting of N,N'-di(1-naphthyl)-N,N'-diphenylbenzidine ($\alpha$-NPD) as a hole-transport layer and 8-tris-hydroxyquinoline aluminum (Alq$_3$) as a light-emitting and electron-transport layer. The insertion of the F$_{16}$CuPC between indium-tin oxide (ITO) and $\alpha$-NPD reduces the operating voltage significantly and thereby increases the luminous efficiency. By measuring the device characteristics for various F$_{16}$CuPC thicknesses, we find that an optimum F$_{16}$CuPC thickness is about 15 nm. At a luminance of 1000 cd/m$^2$, the device with 15-nm-thick F$_{16}$CuPC shows a luminous efficiency of 1.5 lm/W and a device operating voltage of 7.2 V while the device without the F$_{16}$CuPC layer shows 1.1 lm/W and 10.4 V. The significant decrease in a driving voltage and increase in the luminous efficiency can be attributed to the high hole-injection efficiency when F$_{16}$CuPC is inserted between ITO and $\alpha$-NPD