We discuss the photovoltaic effect at a $p\text{−}n$ heterojunction, in which the illuminated side is a doped Mott insulator, using the simplest description of a Mott insulator within the Hubbard model. We find that the energy efficiency of such a device, if we choose an appropriate narrow-gap Mott insulator, can be significantly enhanced due to impact ionization caused by the photoexcited “hot” electron-hole pairs. Namely, the photoexcited electron and/or hole can convert its excess energy beyond the Mott-Hubbard gap to additional electrical energy by creating multiple electron-hole pairs in a time scale which can be shorter than the time characterizing other relaxation processes.

• Received 2 June 2010

DOI:https://doi.org/10.1103/PhysRevB.82.125109