The role of electron photoemission in the 'photoconductivity' of semiconducting polymers

We present the excitation profile of the transient and steady-state photoconductivity of poly(phenylene vinylene) and its soluble derivatives over a wide spectral range up to hv = 6.2 eV. An apparent increase in the 'photoconductivity' at hv > 3-4 eV arises from external current generated by electron photoemission (PE). After quenching the PE by adding a gas mixture of CO2 + SF6 (90%:10%) into the sample chamber, the bulk photoconductivity is nearly independent of photon energy in all polymers studied. The single threshold for photoconductivity is spectrally close to the onset of pi-pi* absorption, a behavior that is inconsistent with a large exciton binding energy. (C) 2001 Elsevier Science B.V. All rights reserved.