Synthesis and Characterization of an Earth-Abundant Cu2BaSn(S,Se)4 Chalcogenide for Photoelectrochemical Cell Application

Cu2BaSnS4-xSex films consisting of earth-abundant metals have been examined for photocathode application. Films with different Se contents (i.e., Cu2BaSnS4-xSex with x <= 2.4) were synthesized using a cosputter system with post-deposition sulfurization/selenization annealing treatments. Each film adopts a trigonal P31 crystal structure, with progressively larger lattice constants and with band gaps shifting from 2.0 to 1.6 eV, as more Se substitutes for S in the parent compound Cu2BaSnS4. Given the suitable bandgap and earth-abundant elements, the Cu2BaSnS4-xSex films were studied as prospective photocathodes for water splitting. Greater than 6 mA/cm(2) was obtained under illumination at -0.4 V versus reversible hydrogen electrode for Pt/Cu2BaSnS4-xSex films with similar to 60% Se content (i.e., x = 2.4), whereas a bare Cu2BaSnS4-xSex (x = 2.4) film yielded similar to 3 mA/cm(2) at -0.4 V/RHE.