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

Abstract

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 8.86cd∕A, which is markedly higher than those, 5.26cd∕A and 0.11cd∕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.