SPECTRAL CHARACTERISTICS OF C-60-CONDUCTING POLYMER JUNCTIONS - VARIOUS MOLECULAR D-A TYPE PHOTOCELLS

We have found recently that thin film layered heterojunction between C -60 and conducting polymer, like poly(3-alkylthiophene) (PAT) shows a photovoltaic effect due to photoinduced charge transfer at the interfa ce. Here we describe two other examples of such photocells in RO-PPV/C -60 and PPP/C-60 heterojunctions and study their spectral characterist ics. Contrary to conventional inorganic semiconductor p-n junction pho tocells, the C-60-PAT junction can be rather viewed as molecular donor -acceptor (D-A) type photocell in which the processes of photogenerati on and separation of charge carriers are quite distinct. In a p-n junc tion free electron-hole pairs are known to be primarily photogenerated at interband transition and then separated in the internal electric f ield of the barrier, while in D-A molecular photocell mainly neutral e xcitons are first created by light, with charges being primarily separ ated at the narrow interface region due to D-A type intermolecular cha rge transfer interactions. We analyze how this processes depend on the wavelength of the pumping light and on the polarity and magnitude of the applied voltage.