CONJUGATED polymers have been incorporated as active materials into se
veral kinds of electronic device, such as diodes, transistors1 and lig
ht-emitting diodes2. The first polymer light-emitting diodes were base
d on poly(p-phenylene vinylene) (PPV), which is robust and has a readi
ly processible precursor polymer. Electroluminescence in this material
is achieved by injection of electrons into the conduction band and ho
les into the valence band, which capture one another with emission of
visible radiation. Efficient injection of electrons has previously req
uired the use of metal electrodes with low work functions, primarily c
alcium; but this reactive metal presents problems for device stability
. Here we report the fabrication of electroluminescent devices using a
new family of processible poly(cyanoterephthalylidene)s. As the lowes
t unoccupied orbitals of these polymers (from which the conduction ban
d is formed) lie at lower energies than those of PPV, electrodes made
from stable metals such as aluminium can be used for electron injectio
n. For hole injection, we use indium tin oxide coated with a PPV layer
; this helps to localize charge at the interface between the PPV and t
he new polymer, increasing the efficiency of recombination. In this wa
y, we are able to achieve high internal efficiencies (photons emitted
per electrons injected) of up to 4% in these devices.