A thin film containing an electron donor (tetraphenyl diamine) quenches the exciton fluorescence and substantially alters the photovoltaic properties of perylene bis(phenethylimide) cells. The film causes the open circuit photovoltage to shift positive by about 450 mV relative to cells without the film. In the case of silver back contacts, the presence of the film inverts the photovoltaic effect relative to that in the absence of the film, and causes the front electrode to become more photoactive than the back. These effects are interpreted as resulting from interfacial exciton dissociation rather than from junction formation. ©1995 American Institute of Physics.