Singlet exciton binding energy in poly(phenylene vinylene)

The exciton binding energy (E(b)) and the band gap energy (E(g)) of poly(phenylene vinylene) are determined by high-resolution measurements of the photoconductivity excitation profile as a function of light polarization, applied electric field, and temperature. At high applied electric fields, a peak in the photoconductivity is observed when the sample is pumped at a photon energy just below the onset of the band-to-band π-π* absorption. This peak is interpreted as resulting from field ionization of a weakly bound exciton with E(b) ≈ 60 meV. The binding energy is obtained from the energy of the exciton peak relative to the band edge and independently from analysis of the dependence of the exciton dissociation on field and temperature.