Photovoltaic properties of C60PPP heterojunction: molecular D-A photocell

We have found recently that thin film layered heterojunction between C60 and conducting polymer, like poly(3-alkylthiophene) shows a photovoltaic effect due to photoinduced charge transfer at the interface. In this work we report the method of fabrication and characterization of AI/C60/PPP/SnO2 junctions and examine its photoresponse. The PPP thin film have been vacuum deposited by discrete (or flash) evaporation of PPP (polyparaphenylene) powder, which allows to avoid the decomposition of polymer chains. Then C60 was evaporated on the top of PPP film. The heterostructure showed the assymmetric I–V dependence with the rectification ratio of about 104 at 20V reverse bias (plus at Al-electrode). Upon illumination the drastic increase of the photocurrent has been observed at reverse bias, suggesting the possible application of this junction as a sensitive photodetector. Spectral response of the device was studied and the mechanisms of the photovoltaic effect are discussed. Contrary to conventional inorganic semiconductor p-n junction photocell, the C60-PPP junction can be rather viewed as molecular donor-acceptor (D-A) type photocell.