Organic electroluminescent devices using variable metal cathode in 4-layer structure

OELDs of ITO/TPD/Alq 3/Metal structure using various metallic materials of Al, Al:Li (0.1 wt%), Al:Li (0.5 wt%), Mg and Mg:Ag (10 wt%) were fabricated to investigate the characteristics of devices according to work function and chemical stability of cathode metal. Mg cathode injects larger amount of electrons into the organic layers than Al with relatively higher work function at the same applied voltage. In the case of Al:Li alloy cathode, Al:Li (0.5 %) induces better injection of electron than Al:Li (0.1 %) and Al itself but sharp decrease of its chemical stability due to oxidation results in short lifetime of device. On the other hand, Mg:Ag (10 %) shows better stability than Al:Li (0.5 %) because Ag is sluggish in respect to self-oxidation and protects oxidation of Mg to achieve relatively longer lifetime.