Y. Yang et Qb. Pei, POLY(1,4-PHENYLENE-1,2-DIPHENYLVINYLENE) AND TRIS(8-QUINOLINOLATO)ALUMINUM BILAYER LIGHT-EMITTING-DIODES, Polymers for advanced technologies, 8(7), 1997, pp. 431-436
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.