High-Quality LaVO Films as Solar Energy Conversion Material.

Mott insulating oxides and their heterostructures have recently been identified as potential photovoltaic materials with favorable absorption properties and an intrinsic built-in electric field that can efficiently separate excited electron-hole pairs. At the same time, they are predicted to overcome the Shockley-Queisser limit due to strong electron-electron interaction present. Despite these premises a high concentration of defects commonly observed in Mott insulating films acting as recombination centers can derogate the photovoltaic conversion efficiency. With use of the self-regulated growth kinetics in hybrid molecular beam epitaxy, this obstacle can be overcome. High-quality, stoichiometric LaVO films were grown with defect densities of in-gap states up to 2 orders of magnitude lower compared to the films in the literature, and a factor of 3 lower than LaVO bulk single crystals. Photoconductivity measurements revealed a significant photoresponsivity increase as high as tenfold of stoichiometric LaVO films compared to their nonstoichiometric counterparts. This work marks a critical step toward the realization of high-performance Mott insulator solar cells beyond conventional semiconductors.