Organic oxide/Al composite cathode in efficient polymer light-emitting diodes

This work presents the fabrication of efficient polymer light-emitting diodes (PLEDs) by thermally evaporating a salt-free neutral organic-oxide buffer layer onto the surface of the electroluminescent film in a vacuum before the device cathode, made of Al-rather than the low work function metals, such as Ca or Ba-is deposited. The electroluminescence (EL) efficiency of phenyl-substituted poly(para-phenylene vinylene) copolymer-based PLEDs with an organic oxide/Al composite cathode, reaches 8.86 cd/A, which is markedly higher than those, 5.26 cd/A and 0.11 cd/A, of devices with Ca/Al and Al cathodes, respectively. The device performance is improved by the formation of a specific organic oxide/Al complex at the cathode interface during the deposition of Al, facilitating the injection of electrons and eliminating the metal-induced quenching sites of luminescence in the EL layer near the recombination region. (c) 2006 American Institute of Physics.