Electronic Materials Letters , vol. 4, no. 2, pp.63-66, June, 2008

DOI :

Increase of Quantum Efficiency in Organic Light Emitting Diodes with Mg-Al Alloy Cathode and RhO₂-Coated ITO Anode

Soo Young Kim, Kihyon Hong, Kisoo Kim, and Jong-Lam Lee^*
Pohang University of Science and Technology (POSTECH)

Abstract : The enhancement of quantum efficiency using a Mg-Al alloy cathode and RhO_x-coated indium tin oxide (ITO) anode in organic light emitting diodes (OLEDs) is reported. The external quantum efficiency at a current density of 128 mA/cm² increased from 0.04% to 0.88% resulting from the Al cathode and ITO anode changing to Mg:Al = 8:2 cathode and RhO_x-coated ITO anode, respectively. The synchrotron radiation photoelectron spectroscopy results show that the work function of the ITO anode increased by 0.2 eV by coating 2 nm thick RhO_x and the work function of the Al cathode decreased by 0.4 eV by alloying the Al with Mg. Thus, both the hole and electron injection energy barriers were simultaneously lowered, which reduced the turn-on voltage and increased the quantum efficiency of the OLEDs.

Keyword : organic light emitting diodes, hole injection barrier, electron injection barrier, x-ray photoemission spectroscopy, O₂ plasma treatment