Synthesis and characterization of transition metal-subtituted indium thiospinels as intermediate band materials for high efficiency solar cells

Abstract

It was recently proposed that higher efficiency can be achieved in PV cells having a single-absorbent if for the latter an intermediate band (IB) material is used which contains a partially filled, isolated band within the gap of an otherwise normal semiconductor. In2S3 and related compounds in which octahedrally coordinated In is substituted by a light transition metal are IB material candidates according to solid state chemistry concepts, this having been confirmed by quantum calculations. Here materials of this type have been chemically synthesized in powder form using wet solvothermal methods. Especially for vanadium-substituted In2S3 , incorporation of the metal into the lattice is supported by XRD and TEM data, and only minor oxidation of vanadium from the V III state to the V IV state is evidenced by EPR. New sub-bandgap features appear in the diffuse reflectance optical spectra upon incorporation of vanadium; these coincide with the spectra that had been predicted by the quantum calculations as corresponding to the IB electronic structure. The realization of the IB concept in a single compound, that furthermore should be easy to prepare in the form needed for PV thin film cells, is thus achieved for the first time.