POLY(1,4-PHENYLENE-1,2-DIPHENYLVINYLENE) AND TRIS(8-QUINOLINOLATO)ALUMINUM BILAYER LIGHT-EMITTING-DIODES

A bilayer polymer light-emitting diode has been demonstrated. This bil ayer structure is composed of two different materials with nearly iden tical luminescent spectra, but different band positions. The band stru cture of one material, poly(1,4-phenylene-1,2-diphenylvinylene), favor s hold injection, while the band structure of the other material, tris -(8-quinolinolato)aluminum, favors electron injection. Therefore in th is device structure, a heterojunction forms at the bilayer interface. Charges injected from the anode and cathode accumulated at this interf ace and subsequently radiative recombine. Compared with the single-lay er devices made from each of these two materials, the device performan ce of this bilayer LED is significantly improved owing to this carrier localization. Device quantum efficiency is enhanced by a factor of 20 to reach similar to 1% photons/electron. Unlike some other bilayer sy stems, there is no color shift of this bilayer structure, because the luminescent spectra are the same for both materials. (C) 1997 by John Wiley & Sons, Ltd.