Efficiency dependence on alkali metal compound/Al bilayer cathode in organic light-emitting diodes

Abstract

The use of alkali metal compound/Al bilayer cathodes of LiF/Al and Liq/Al caused a dramatic luminous efficiency change of one order of magnitude in organic light-emitting diodes (OLEDs) comprising 2-methyl-9,10-bis(naphthalene-2-yl)anthracene (MADN) as an electron-transporting layer (ETL). In contrast, the use of the same two electrodes yielded similar efficiency in OLEDs comprising of tris(8-hydroxyquinoline) aluminum(III) (Alq3) as an ETL. The dramatic change is attributed to different behaviors of LiF/Al and Liq/Al cathodes toward the ETL. It is revealed that organic alkali metal complex/Al, such as Liq/Al, is superior to inorganic alkali metal compound/Al, such as LiF/Al, as a standard bilayer cathode to investigate the effectiveness of electron-transporting materials for high-efficiency OLEDs.