  Intermediate band semiconductors hold the promise to significantly improve
the efficiency of solar cells, but only if the intermediate impurity band is
metallic. We apply a recently developed first principles method to investigate
the origin of electron localization in Ti doped Si, a promising candidate for
intermediate band solar cells. Although Anderson localization is often
overlooked in the context of intermediate band solar cells, our results show
that in Ti doped Si it plays a more important role in the metal insulator
transition than Mott localization. Implications for the theory of intermediate
band solar cells are discussed.
