Modelling potential photovoltaic absorbers Cu₃MCh₄ (M = V, Nb, Ta; Ch = S, Se, Te) using density functional theory

The geometric and electronic properties of a series of potential photovoltaic materials, the sulvanite structured Cu₃MCh₄ (M = V, Nb, Ta; Ch = S, Se, Te), have been computationally examined using both PBEsol+U and HSE06 methods to assess the materials' suitability for solar cell application and to compare the predictions of the two theoretical approaches. The lattice parameters, electronic density of states, and band gaps of the compounds have been calculated to ascertain the experimental agreement obtained by each method and to determine if any of the systems have an optical band gap appropriate for photovoltaic absorber materials. The PBEsol+U results are shown to achieve better agreement with experiment than HSE06 in terms of both lattice constants and band gaps, demonstrating that higher level theoretical methods do not automatically result in a greater level of accuracy than their computationally less expensive counterparts. The PBEsol+U calculated optical band gaps of five materials suggest potential suitability as photovoltaic absorbers, with values of 1.72 eV, 1.49 eV, 1.19 eV, 1.46 eV, and 1.69 eV for Cu₃VS₄, Cu₃VSe₄, Cu₃VTe₄, Cu₃NbTe₄, and Cu₃TaTe₄, respectively, although it should be noted that all fundamental band gaps are indirect in nature, which could lower the open-circuit voltage and hence the efficiency of prospective devices.