Porous Cu₂BaSn(S,Se)₄ Film as a Photocathode Using Non-Toxic Solvent and a Ball-Milling Approach

Cu2BaSn(S,Se)4 (CBTSSe) has been proposed as an alternative to Cu2ZnSn(S,Se)4 (CZTSSe) for solar absorbers due to its reduced propensity for antisite disorder and band tailing while maintaining the desirable characteristics of band gap tunability, earth-abundance, and low toxicity constituent metals. However, current film deposition methods require high-vacuum conditions or toxic solvents, which are less desirable features for prospective large-scale production. In this paper, ball milling is demonstrated as a route toward a scalable processing method for CBTSSe, using a precursor ink consisting of common elements Cu2S, BaS, Sn, and S in low-toxicity ethanol. A final film with a thickness and average grain size on the order of 1 μm was synthesized with a band gap of 1.56 eV, corresponding to a Cu2BaSnS4–xSex (x ≈ 3) stoichiometry. A porous CBTSSe photocathode with Pt/TiO2/CdS overlayers was fabricated to demonstrate the photocurrent-generating capabilities of the film, yielding current densities as high as 5.54 mA/cm2 at 0 V versus a reversible hydrogen electrode (V/RHE).