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

Abstract

Cu₂BaSnS_4–<i>x</i>Se_<i>x</i> films consisting of earth-abundant metals have been examined for photocathode application. Films with different Se contents (i.e., Cu₂BaSnS_4–<i>x</i>Se_<i>x</i> with <i>x</i> ≤ 2.4) were synthesized using a cosputter system with post-deposition sulfurization/selenization annealing treatments. Each film adopts a trigonal <i>P3</i>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 Cu₂BaSnS₄. Given the suitable bandgap and earth-abundant elements, the Cu₂BaSnS_4–<i>x</i>Se_<i>x</i> films were studied as prospective photocathodes for water splitting. Greater than 6 mA/cm² was obtained under illumination at −0.4 V versus reversible hydrogen electrode for Pt/Cu₂BaSnS_4–<i>x</i>Se_<i>x</i> films with ∼60% Se content (i.e., <i>x</i> = 2.4), whereas a bare Cu₂BaSnS_4–<i>x</i>Se_<i>x</i> (<i>x</i> = 2.4) film yielded ∼3 mA/cm² at −0.4 V/RHE