Dependence of efficiency improvement and operating-voltage reduction of OLEDs on thickness variation in the PTFE hole-injection layer

Abstract

In a device structure of ITO/hole-injection layer (PTFE)/tris(8-hydroxyquinoline) aluminum (Alq(3))/Al, the dependence of the efficiency improvement of organic light-emitting diodes (OLEDs) on thickness variation in the PTFE hole-injection layer was investigated. The PTFE used for a hole-injection layer helps in improving the performance of the device in several aspects, such as improved efficiency, lower operating voltage, band energy-band adjustment. The device was manufactured using thermal evaporation under a base pressure of 5 x 10(-6) Torr. The Alq(3) organics were evaporated to be 100 nm thick at a deposition rate of 1.5 angstrom/s, and the PTFE layer thickness was varied from 0 to 3.0 nm. The obtained optimum thickness of PTFE layer was 2.5 nm from the electrical characteristics. With the PTFE layer, the luminous efficiency and the external quantum efficiency were improved by factors of 21 and 12, respectively, and the operating voltage was reduced to 3 V.