We present results on metal-containing sulphides which we propose, based on ab-initio DFT calculations, as having Intermediate Band (IB) electronic characteristics like those allowing the construction of highly efficient PV cells. We synthesized V-containing SnS2, one of those systems, and have proven with a photocatalytic test that sub-bandgap photons generate in it electrons and holes. We check that Van der Waals interactions between the X-M-X sandwiches parallel to the (0001) plane in its structure must be included in its DFT modelling to get correct results. We model also the stability of different V-doping configurations proving that those which lead to an IB and reproduce the observed paramagnetism are metastable (the most stable configuration leads to V-V pairing), so that nonequilibrium synthesis methods are essential to prepare a material with an IB. We also study V-doped ZnIn2S4, another Van der Waals-layered structure showing an IB in the DFT calculations. We prepared this material, which also displays in the optical spectrum sub-bandgap photon absorption matching the DFT results, and have carried out on it the same photocatalytic test, which shows as well photoactivity with sub-bandgap photons, but less marked than in the cases of V:SnS2 or V:In2S3, the best of our systems to date. Finally we report how a photocatalytic test using dissolved compounds which react selectively with trapped electron or hole species can check separately the behaviour of these latter.

Trabajo presentado en el E-MRS 2013 Spring Meeting, celebrado en Estrasburgo (Francia) del 27 al 31 de mayo de 2013.

Peer Reviewed