Photoconduction in oligo-para-phenylenevinylene films

Abstract

Steady state photoconduction was studied in optically thin spin coated and optically thick solution grown films of an oligo-para-phenylenevinylene sandwiched between indium tin oxide (ITO) and aluminum (Al) contacts. Oligomers represent model systems for polyphenylenevinylene that do not contain structural irregularities and impurities always present in polymers. Upon irradiation through the positively biased ITO contact, dissociation of excited states via electron transfer to the ITO prevails. It leads to a field and temperature dependent photocurrent that is symbatic with the absorption spectrum. The efficiency of this process increases with excess energy of the primarily excited state. Photocurrents due to bulk photoionization are observed upon irradiating through the positively biased Al contact. They result from temperature and field assisted dissociation of geminate e–h pairs generated either by field induced break-up of molecular singlet states or by direct charge transfer transition.