Interfacial chemistry of Sm with Alq3 and its implication to organic light-emitting devices

Interfacial chemistry of samarium (Sm) with tris-(8-hydroxyquinoline) aluminum (Alq3) has been investigated. Photoelectron analysis revealed strong interactions at the Sm–Alq3 interface and limited Sm diffusion into Alq3. The lowest unoccupied molecular orbital of Alq3 was found to be 0.28 eV below the Fermi level of Sm at the Sm–Alq3 contact, implying lacking a barrier to electron-injection from the Sm to Alq3. Replacing Sm for MgAg as a cathode in organic electroluminescent devices considerably improved current–voltage characteristics, while the device efficiency was found to decrease by 40%. The reduction in efficiency is attributed to low optical reflectance at the Sm–Alq3 interface.