PHOTOGENERATION IN CONDUCTING POLYMERS

A number of diverse phenomena, such as the small carrier yield pet pho ton seen in picosecond photoconductivity, the different behavior of pi cosecond photoinduced absorption, PA, in dilute solutions and thin fil ms, and the spectral distribution of PA in thin films, show that photo generated positive and negative polarons in conducting polymers are fo r the most part bound in pairs on adjacent chains by their Coulomb att raction. The PA also gives additional evidence that the binding energy of the singlet exciton in poly (phenylene vinylene) is 0.4 eV, leadin g to a gap of 2.8 eV.