Organic electroluminescent devices using variable metal cathode in 4-layerstructure

OELDs of ITO/TPD/Alq(3)/Metal structure using various metallic materials of Al, Al:Li (0.1 wt%), AI:Li (9.5 wt%), Mg and Mg:Ag (10 wt%) were fabricate d to investigate the characteristics of devices according to work function and chemical stability of cathode metal. Mg cathode injects larger amount o f electrons into the organic layers than Al with relatively higher work fun ction at the same applied voltage. In the case of AI:Li alloy cathode, AI:L i (0.5%) induces better injection of electron than AI:Li (0.1%) and Al itse lf 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 stab ility than AI:Li (0.5%) because Ag is sluggish in respect to self-oxidation and protects oxidation of Mg to achieve relatively longer lifetime.