Our research aims to develop plastic films that change the colour of the light that passes through them, not by absorbing certain wavelengths of light, as a simple colour filter would, but by converting light of one wavelength to another without losing any energy. Such a film, applied to a silicon solar cell, could make it up to 30% more efficient. To do this we need to make semiconductor nanocrystals, coat them with a very thin layer of an organic semiconductor so the two materials are in molecular contact. Then we have to disperse these tiny composite nanoparticles in a clear plastic film, as evenly as possible and without clumping. Small angle neutron scattering allows to pick out the shapes of the composite nanoparticles and their component parts, and the way they interact each other, helping us to design routes to make these "photon multiplier" films.