The role of electron photoemission in the `photoconductivityʹ 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 hν=6.2 eV. An apparent increase in the `photoconductivityʹ at hν>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 π–π∗ absorption, a behavior that is inconsistent with a large exciton binding energy.