EXCITON DIFFUSION AND DISSOCIATION IN A POLY(P-PHENYLENEVINYLENE) C-60 HETEROJUNCTION PHOTOVOLTAIC CELL/

We report measurements of the photovoltaic response of two-layer photo cells formed with layers of the conjugated polymer poly(phenylenevinyl ene), PPV and fullerene, C-60, formed between indium-tin oxide and alu minum electrodes. Peak quantum efficiencies of up to similar to 9% (el ectrons collected per incident photon) were measured under short-circu it conditions. We model the photovoltaic response as arising from exci tons photogenerated in the PPV layer which are able to diffuse to the interface with the C-60 layer where they are ionized. We obtain a valu e for the exciton diffusion range of 7+/-1 nm, both from the spectral response and from the absolute efficiency. We demonstrate that the bra nching ratio for the creation of singlet excitons from absorbed photon s is close to unity. (C) 1996 American Institute of Physics.