PHOTOVOLTAIC PROPERTIES OF C-60 PPP HETEROJUNCTION - MOLECULAR D-A PHOTOCELL/

We have found recently that thin film layered heterojunction between C -60 and conducting polymer, like poly(3-alkylthiophene) shows a photov oltaic effect due to photoinduced charge transfer at the interface. In this work we report the method of fabrication and characterization of Al/C-60/PPP/SnO2 junctions and examine its photoresponse. The PPP thi n film have been vacuum deposited by discrete (or flash) evaporation o f PPP (polyparaphenylene) powder, which allows to avoid the decomposit ion of polymer chains. Then C-60 was evaporated on the top of PPP film . The heterostructure showed the assymmetric I-V dependence with the r ectification ratio of about 10(4) at 20V reverse bias (plus at Al-elec trode). 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 d iscussed. Contrary to conventional inorganic semiconductor p-n junctio n photocell, the C-60-PPP junction can be Father viewed as molecular d onor-acceptor (D-A) type photocell.