  We propose an unexplored class of absorbing materials for high-efficiency
solar cells: heterostructures of transition-metal oxides. In particular, LaVO_3
grown on SrTiO_3 has a direct band gap ~1.1 eV in the optimal range as well as
an internal potential gradient, which can greatly help to separate the
photo-generated electron-hole pairs. Furthermore, oxide heterostructures afford
the flexibility to combine LaVO_3 with other materials such as LaFeO_3 in order
to achieve even higher efficiencies with band-gap graded solar cells. We use
density-functional theory to demonstrate these features.
