Photogeneration in conducting polymers

A number of diverse phenomena, such as the small carrier yield per photon seen in picosecond photoconductivity, the different behavior of picosecond photoinduced absorption, PA, in dilute solutions and thin films, and the spectral distribution of PA in thin films, show that photogenerated positive and negative polarons in conducting polymers are for the most part bound in pairs on adjacent chains by their Coulomb attraction. The PA also gives additional evidence that the binding energy of the singlet exciton in poly (phenylene vinylene) is 0.4 eV, leading to a gap of 2.8 eV.