Optical Effect due to Thickness Variation of Electron Injection Layer in Organic Light-emitting Diodes

Abstract

Organic light-emitting diodes (OLEDs) are attractive because of possible application in display with low-operating voltage, low-power consumption, self-emission and capability of multicolor emission by the selection of emissive materials. To investigated the optical effects, we studied the electrical and optical characteristics due to thickness variation of electron injection materials LiF on organic light-emitting diodes in the ITO (indium-tin-oxide)/N,N'-diphenyl-N,N'-bis(3-methyphenyl)-1,1'-biphenyl-4,4'-diamine(TPD)/tris(8-hydroxyquinoline) aluminum (Alq₃)/LiF layer/Al device. We maintained the thicknesses of TPD and Alq₃ layers at 40 nm and 60 nm, respectively. The deposition rates of TPD and Alq3 were in the 1.5 Å/s under a base pressure of 5x10-6 Torr. It was found that luminance and luminous efficiency of the device with 0.7 nm LiF layer improve 25 times and 7 times than the device without the LiF layer, respectively.