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Exciton diffusion and dissociation in a poly(<i>p</i>-phenylenevinylene)/C60 heterojunction photovoltaic cell
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1996
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EngineeringOrganic Solar CellPhotovoltaic DevicesOptoelectronic DevicesChemistryPhotovoltaicsSemiconductorsExciton DiffusionElectronic DevicesPhotodetectorsSolar Cell StructuresPpv LayerPhotochemistryOptoelectronic MaterialsOrganic SemiconductorC60 LayerExciton Diffusion RangeApplied PhysicsConjugated PolymerSolar CellsOptoelectronicsSolar Cell Materials
The authors fabricated two‑layer PPV/C60 photovoltaic cells on ITO/Al electrodes and modeled their response as excitons generated in PPV diffusing to the PPV/C60 interface where they are ionized. The devices achieved peak quantum efficiencies of ~9 %, an exciton diffusion length of 7 ± 1 nm, and a singlet‑exciton generation branching ratio near unity.
We report measurements of the photovoltaic response of two-layer photocells formed with layers of the conjugated polymer poly(phenylenevinylene), PPV and fullerene, C60, formed between indium-tin oxide and aluminum electrodes. Peak quantum efficiencies of up to ∼9% (electrons collected per incident photon) were measured under short-circuit conditions. We model the photovoltaic response as arising from excitons photogenerated in the PPV layer which are able to diffuse to the interface with the C60 layer where they are ionized. We obtain a value for the exciton diffusion range of 7±1 nm, both from the spectral response and from the absolute efficiency. We demonstrate that the branching ratio for the creation of singlet excitons from absorbed photons is close to unity.