Top emission inverted organic light emitting diodes with $N_{2}$ plasma treated Al bottom cathodes

Effects of $N_{2}$ plasma treatment of the Al bottom cathode on the characteristics of top emission inverted organic light emitting diodes (TEIOLEDs) were studied. TEIOLEDs were fabricated by depositing an Al bottom cathode, a tris-(8-hydroxyquinoline) aluminum $(Alq_{3})$ emitting layer, an N,N'-diphenyl-N,N'-bis(3-methylphenyl)-1,1'-diphenyl-4,4'diamine (TPD) hole transport layer, and an indium tin oxide (ITO) top anode sequentially. The Al bottom cathode layer was subjected to $N_{2}$ plasma treatment before deposition of the $Alq_{3}$ layer. X-ray photoelectron spectroscopy suggested that the existence of and the amount of $AIN_x$ between the $Alq_{3}$ emitting layer and the Al bottom cathode significantly affect the characteristics of TEIOLEDs. The maximum external quantum efficiency of the TEIOLED with an Ai bottom cathode subjected to $N_{2}$ plasma treatment for 30 s was about twice as high as that of the TEIOLED with an untreated Al bottom cathode.