While the hole transport decreased in the mixed layer in the organic light-emitting devices (OLEDs) with an Al:lithium quinolate (Liq) mixed layers in the electron transport layer (ETL), the electron injection increased the Al:Liq mixed layer. The enhancement of luminance efficiency in the OLEDs with an Al:Liq mixed layer in the ETL originated from the more balance between the electrons and the holes in the emitting layer due to the decrease in the hole injection and the increase in the electron injection resulting from the existence of the Al:Liq mixed layer.