Synthesis and Characterization of an Earth-Abundant Cu 2 BaSn(S,Se) 4 Chalcogenide for Photoelectrochemical Cell Application.

Cu ₂ BaSnS _4-x Se _x films consisting of earth-abundant metals have been examined for photocathode application. Films with different Se contents (i.e., Cu ₂ BaSnS _4-x Se _x with x ≤ 2.4) were synthesized using a cosputter system with post-deposition sulfurization/selenization annealing treatments. Each film adopts a trigonal P3 ₁ 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 Cu ₂ BaSnS ₄ . Given the suitable bandgap and earth-abundant elements, the Cu ₂ BaSnS _4-x Se _x 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/Cu ₂ BaSnS _4-x Se _x films with ∼60% Se content (i.e., x = 2.4), whereas a bare Cu ₂ BaSnS _4-x Se _x (x = 2.4) film yielded ∼3 mA/cm ² at -0.4 V/RHE.