A bulk heterojunction comprising an intermixed blend of fully inorganic n- and p-type particles and its method of manufacture are described. The particles are preferably nanometer-scale, spherical-shaped particles known as nanocrystals which are assembled into a densely packed three-dimensional array. The nanocrystals are preferably fabricated from a photo-active material which, in combination with the nanocrystal shape and size, can be engineered to produce a bulk heterojunction with a specific absorption spectrum. The bulk heterojunction is preferably formed by dispersing a predetermined ratio of the desired n- and p-type nanocrystals in an organic solvent and employing low-cost solution processing techniques to deposit a film having the desired thickness, relative concentration of nanocrystal types, and degree of intermixing onto a substrate. When incorporated as the active layer in optoelectronic devices such solar cells, fully inorganic bulk heterojunctions offer significant improvements in performance while maintaining the low costs associated with organic processing techniques.
 The present invention was made with Government support under Contract No. DE-AC02-98CH10866 awarded by the U.S. Department of Energy. The United States Government has certain rights in the invention.