Self-Regulated Growth and Tunable Properties of CuSbS2 Solar Absorbers

Abstract Polycrystalline thin film copper chalcogenide solar cells show remarkable efficiencies, and analogous but less-explored semiconducting materials may hold similar promise. With consideration of elemental abundance and process scalability, we explore the potential of the Cu–Sb–S material system for photovoltaic applications. Using a high-throughput combinatorial approach, Cu–Sb–S libraries were synthesized by magnetron co-sputtering of Cu 2 S and Sb 2 S 3 targets and evaluated by a suite of spatially resolved characterization techniques. The resulting compounds include Cu 1.8 S (digenite), Cu 12 Sb 4 S 13 (tetrahedrite), CuSbS 2 (chalcostibite), and Sb 2 S 3 (stibnite). Of the two ternary phases synthesized, CuSbS 2 was found to have the most potential, however, when deposited at low temperatures its electrical conductivity varied by several orders of magnitude due to the presence of impurities. To address this issue, we developed a self-regulated approach to synthesize stoichiometric CuSbS 2 films using excess Sb 2 S 3 vapor at elevated substrate temperatures. Theoretical calculations explain that phase-pure CuSbS 2 is expected to be formed over a relatively wide range of temperatures and pressures, bound by the sublimation of Sb 2 S 3 and decomposition of CuSbS 2 . The carrier concentration of CuSbS 2 films produced within this regime was tunable from 10 16 – 10 18 cm − 3 through appropriate control of Sb 2 S 3 flux rate and substrate temperature. CuSbS 2 displayed a sharp optical absorption onset indicative of a direct transition at 1.5 eV and an absorption coefficient of 10 5  cm −1 within 0.3 eV of the onset. The results of this study suggest that CuSbS 2 holds promise for solar energy conversion due to its tolerant processing window, tunable carrier concentration, solar-matched band gap, and high absorption coefficient.