Fe-doped CuInSe2: An ab initio study of magnetic defects in a photovoltaic material

Iron substitution in CuInSe2 could have important implications either for photovoltaic or spintronic applications. To better understand the Fe effects, we have performed density functional calculations on the CuInSe2 chalcopyrite as well as on Fe-doped derivative compounds with different concentrations and geometries. The defect formation energies of Fe-In and Fe-Cu substitutions for different Fe/metal concentrations (6.25% to 100%) have been determined and we have shown that these energies fluctuate with the Fe content depending on concentration and magnetic ordering. In these Fe-substituted adamantine structures, the antiferromagnetic state has been found to be most of the time more stable than the ferromagnetic state. The magnetic moment of the iron atom was found to slightly decrease with the amount of substituted Fe. The antiferromagnetic to ferromagnetic transition temperatures have been determined by Monte Carlo methods and have been found to be around 100 K in most instances. The analysis of the densities of states was used to make predictions on the influence on photovoltaic performance improvement and on spintronic properties induced by substitutional Fe atoms. For the case of CuInSe2, Fe impurities are expected to impart to the material spintronic properties, depending on the site in which it is substituted, but to degrade its photovoltaic properties.