Experimental evidence of electron transfer from photo-excited conjugated polymers onto C60 is reported. Photoinduced optical absorption, photoinduced electron spin resonance, and quenching of the photoluminescence in conducting polymers interacting with C60 imply that charge transfer from the excited state of the conducting polymer to C60 occurs on a picosecond time scale. The charge-separated state in composite films is metastable at low temperatures. Rectifying bilayer heterojunctions (diodes) have been fabricated using semiconducting polymers and C60; rectification ratios in the current vs. voltage characteristics exceed 104. When illuminated, the devices act as photodiodes and exhibit photovoltaic response as a result of photoinduced charge separation across the heterojunction interface from the semiconducting polymer (donor) onto the C60 (acceptor). The photodiode and photovoltaic responses are characterized. The results are discussed in terms of opportunities for solar energy conversion, for photodiode detector devices, and for a variety of other applications which use photoinduced intermolecular charge separation.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.