Organic semiconductor nanoparticles provide a potentially scalable approach for photovoltaics that can be processed from aqueous media. Particles of poly(3-hexylthiophene) (P3HT):phenyl-C61-butyric acid methyl ester (PCBM) were prepared using two techniques; those produced by a mini-emulsion method contained greater amounts of crystalline P3HT domains with charge generation resembling phase-separated annealed solvent-cast films.