Self-regulated growth and tunable properties of CuSbS2 solar absorbers

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 Cu2S and Sb2S3 targets and evaluated by a suite of spatially resolved characterization techniques. The resulting compounds include Cu1.8S (digenite), Cu12Sb4S13 (tetrahedrite), CuSbS2 (chalcostibite), and Sb2S3 (stibnite). Of the two ternary phases synthesized, CuSbS2 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 CuSbS2 films using excess Sb2S3 vapor at elevated substrate temperatures. Theoretical calculations explain that phase-pure CuSbS2 is expected to be formed over a relatively wide range of temperatures and pressures, bound by the sublimation of Sb2S3 and decomposition of CuSbS2. The carrier concentration of CuSbS2 films produced within this regime was tunable from 10(16)-10(18) cm(-3) through appropriate control of Sb2S3 flux rate and substrate temperature. CuSbS2 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 CuSbS2 holds promise for solar energy conversion due to its tolerant processing window, tunable carrier concentration, solar-matched band gap, and high absorption coefficient. (C) 2014 Elsevier B.V. All rights reserved.