Bright organic electroluminescent devices having a metal-doped electron-injecting layer

Bright organic electroluminescent devices were developed using a metal-doped organic layer as an electron-injecting layer at the interface between the cathode and the emitter layer. The typical device structure is a glass substrate/indium-tin oxide/arylamine/tris(8-quinolinolato)Al (Alq)/metal-doped Alq/Al. Dopant metals are highly reactive metals such as Li, Sr, and Sm. A device with Li-doped Alq layer showed high luminance of over 30 000 ${\mathrm{cd/m}}^{\mathrm{2}},$ while a device without the metal-doped Alq layer exhibited only 3400 ${\mathrm{cd/m}}^{\mathrm{2}}.$ These results suggest that the Li doping to the Alq layer generates the radical anions of Alq serving as intrinsic electron carriers, which result in low barrier height for electron injection and high electron conductivity of the Li-doped Alq layer.