The Electronic Consequences of Multivalent Elements in Inorganic Solar Absorbers: Multivalency of Sn in Cu2ZnSnS4

Multivalent transition metal impurities in semiconductors are known to create deep levels inside the band gap that are associated with changes in the oxidation state. Some emerging functional semiconductor materials now contain multivalent elements not just as impurities, but as part of their structural skeleton ("multivalent semiconductors"). This raises the possibility that the performance of such materials may be affected by those skeleton elements transitioning from one oxidation state to another, in response to charge-altering perturbations such as illumination or doping. Here we address the correlation between multivalency and the electronic properties of these new semiconductor materials.