EXCITON DISSOCIATION AT A POLY(P-PHENYLENEVINYLENE) C-60 HETEROJUNCTION

We report measurements of the photovoltaic effect in heterojunction st ructures consisting of a layer of C-60 thermally evaporated onto a fil m of the conjugated polymer poly (p-phenylenevinylene) (PPV) sandwiche d between electrodes of indium-tin oxide and Al. Peak quantum efficien cies of up to about 9% (electrons collected per incident photon) were measured under short-circuit conditions, with corresponding open-circu it voltages approaching 0.9 V. Increased quantum yields were obtained under forward and reverse biases. We model the response as arising fro m the dissociation of photogenerated excitons at the PPV/C-60 interfac e, with electron transfer to the C-60. The C-60 layer acts as a dielec tric spacer, providing a constructive enhancement of the optical field s at the PPV/C-60 interface. We have applied this model to estimate an exciton diffusion range of 60 to 80 Angstrom.