Towards an ab-initio characterization of novel intermediate band photovoltaic materials

An ab-initio study of novel photovoltaic materials with enhanced optoelectronic properties is presented in this contribution. Predictions of absorption coefficients agree completely with the characterization of the first experimental samples grown in the laboratory. Compounds selected for the study are derived from chalcogenide semiconductors in which several atoms are substituted by transition elements. These atoms modify the electronic band structure in such a way that a new narrow band appears inside the parent semiconductor band-gap. Partial occupation of this band enables that additional carriers could be obtained from absorption of photons with energy lower than that of the band-gap, thus enhancing the photovoltaic conversion properties of the material. It was estimated than a photovoltaic solar cell designed from this novel concept could reach a thermodynamic efficiency of 63.2% compared to 43.1% corresponding to the thermodynamic efficiency limit of conventional semiconductor based solar cells. Results show a significant enhancement of the absorption coefficient respecting to the corresponding parent semiconductor in the main emission region of the solar spectrum. For some of the theoretically proposed compounds, optoelectronic properties of recently synthesized samples have been obtained experimentally. Comparison of experimental absorption measurements with results of the calculations presented here shows a very good agreement.