Computational study of molybdenum trioxide as an intermediate band material

In a solar cell a material with an intermediate band between the conduction and valence bands facilitates the absorption of two below band-gap photons, increasing the maximum theoretical efficiency to 63% from 40% for a conventional cell. In this work, the formation of an intermediate band in molybdenum trioxide with sub-stoichiometry is investigated by use of density functional theory. Van der Waals exchange correlation functionals are tested to find which most accurately models the unique layered structure of MoO3. It is shown that oxygen reduction shifts Mo 4d states from the empty conduction band into the band gap and provides electrons to occupy these states. Electronic structures with resulting gap states are calculated with respect to the position and concentration of oxygen vacancies.