Electroluminescent and photovoltaic properties of the crosslinkable poly(phenylene vinylene) derivative with side chains containing vinyl groups

The photoluminescence (PL), electroluminescence (EL), and photovoltaic properties of a poly(phenylene vinylene) derivative with its side chains containing vinyl groups, poly [(2,5-bis-allyloxyphenylene vinylene)-co-(2-methoxy-5-(2'-ethylhexyloxy)phenylene vinylene)] (A-PPV) are reported. A-PPV with the active vinyl units in the end of its side chains can be crosslinked either by UV light irradiation or heating. The crosslinking does not change the color of light emitted from the A-PPV polymer light-emitting diode (PLED). FTIR confirms that the photo/heating-induced crosslinking does not damage the conjugation of polymer at all. However, the PL and EL efficiency of A-PPV decreased upon photoirradiation due to the existence of residual radicals in the solid-state film. The relatively stable radicals function as a trap that quenches the luminescence. The blend of A-PPV and noncrosslinkable polymer, poly (2-methyl oxy-5-ethylhexyloxyl-1,4-phenylene vinylene) (MEH-PPV) was employed in the fabrication of PLEDs, and the PLED shows improved performance with a luminous efficiency of > 1 cd. A(-1) . The blend keeps the advantage of crosslinkability of the polymers and lessens the effects of the photo-produced radicals. The photovoltaic cells comprised of A-PPV and C-60 were fabricated and the energy conversion efficiency of the devices with and without UV treatment was similar, both around 0.3%. The UV irradiation on the blend film with C-60 seems resistant to the residual radicals.