Highly efficient top-emitting organic light-emitting devices with aluminium electrodes.

Top-emitting organic light-emitting diodes (OLEDs) using aluminium (Al) and nickel (Ni) as the anode and Al as the semitransparent cathode were developed. Hole injection was largely improved by spin coating poly(ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT) on the metal anode. For top-emitting OLEDs with a configuration of metal anode/PEDOT/NPB/Alq3/LiF/Al/Alq3, both devices using Al and Al/Ni anodes showed efficient green light emission with a narrow emission peak. Current efficiency was increased from 4.32 cd A-1 to 6.45 cd A-1 when replacing high work function Ni with low work function Al as the anode. A luminance of 20 000 cd m-2 can be achieved for these top-emitting OLEDs. The device made with the Al/Ni anode showed a low driving voltage and high power efficiency as compared to that made with the Al anode. The improvement on light-emitting efficiency was attributed to balanced charge carrier injection and utilization of the high reflective semitransparent Al cathode. [ABSTRACT FROM AUTHOR]