Bandgap engineering by cationic disorder: case study on AgBiS2.

The influence of cationic disorder on the electronic structure of ternary compounds, here exemplified on AgBiS2 material, is studied by means of accurate first principles periodic density functional theory based calculations. For AgBiS2 cationic disorder in going from semiconducting matildite to a metallic arrangement crystal structure is found to induce a significant decrease in the band gap, as a result of cation-disorder conduction band tail states penetrating into the matildite bandgap. Properly aligned conduction band minimum and valence band maximum show that cationic disorders lead to a noticeable drop of the former and a slight increase of the latter. The present results indicate that temperature effects triggering cationic disorder will have a beneficial effect on the photoactivity of AgBiS2 samples provided that the metallic limit is not reached.