Colloidal dispersions of organic semiconducting nanoparticles (NPs) have shown promise for the generation of active layers in organic solar cells.Composite NPs containing a mixture of an electron donor and an electron acceptor are favoured to maximise the performance of the device. However, the exact location of the donor-acceptor material within each individual NP will affect the amount of photocurrent generated and this is highly dependent on the conditions used to synthesise the nanoparticles. In this study, contrast variation small-angle neutron scattering will be used to probe the internal organisation of composite nanoparticles prepared under different synthesis conditions (concentration, donor/acceptor ratio, solvent mixture). The structural organisation will be correlated with the performance of devices prepared using these materials to determine the optimum configuration.