Effect of anode and cathode workfunction on the operating voltage and luminance of a single emissive layer organic light emitting diode

Abstract

Organic light emitting diodes (OLED) are considered to be a promising candidate for light sources as well as for flat panel display because of their numerous advantageous. Two important parameters of an OLED among many other parameters to measure OLED performance are operating voltage and luminance. Those two parameters are believed to be strongly influenced by an anode and cathode workfunction of materials used as electrodes. In this paper, we study the effect of anode and cathode workfunction on the operating voltage and luminance of a single emissive layer organic light emitting diode. Devices with five different cathodes: Aluminum (Al), Calcium (Ca), Magnesium (Mg), Argentum (Ar), and Cuprum (Cu) and three different anodes: Indium Thin Oxide (ITO), Poly-(3,4-Ethylenedioxidythiophene)-Poly (Styrene Sulfonate) (PEDOT:PSS), Zinc Oxide (ZnO) are compared and analyzed. A 2 nm thick of Polyfluorene (PFO) is used as an emissive layer. SimOLED is used to simulate and analyze both electrical and optical characteristics. Current voltage luminance (IVL) characteristics are simulated under forward biased from 0 to 10 V. We found that the use of anode with higher workfunction can reduce operating voltage as well as increases device luminance. On the other hand, the use of lower workfunction of cathode can reduce operating voltage however it is not always increasing device luminance. The decrease of the operating voltage by increasing anode workfunction and decreasing cathode workfunction are ascribed to the barrier lowering of the holes and the electrons respectively.