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An ab initio study of several compounds candidates to behave as intermediate band materials is presented. The use of these materials as the active element in solar cells is a promising way to enhance the photovoltaic efficiency. Indeed from this point of view, most interesting compounds are those whose host semiconductor presents a band-gap close to the optimum value of 2 eV. Chalcogenide compounds substituted by light transition metals are solid candidates to this end. While they are being further characterized and experimentally synthesized, another approach is being examined. It consists of using Si as host semiconductor. Ti implantation at concentrations several orders of magnitude above equilibrium solubility has shown a probable intermediate band material behavior, the origin of the intermediate band being related to levels of interstitial Ti. Optoelectronic characterization of this material is completed. A novel possibility consists of combining chalcogen S implantation with boron. In this case preliminary results of electronic structure are shown.

An intermediate-band material based on thiospinel semiconductor MgIn2S4is presented. This material is proposed as high efficiency photovoltaic material for intermediate-band solar cells. We analyze V substitution for In in the parent compound MgIn2S4and the formation of the V d-states intermediate band. For the proper characterization of the width and position of this band inside the band gap, the standardone-shotGW method within the plasmon-pole approximation is applied. The electronic properties thus obtained are discussed and compared to those studied with Density Functional Theory (DFT), and the advantages and the limitations of the two methods are discussed. In addition, DFT electronic-charge density analysis is shown.