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.

Two-stage co-evaporated CuSbS2 thin films for solar cells

“…Further increase in the substrate temperature leads to an entire phase change to Cu 12 Sb 4 S 13 , which is in accordance with the result in Ref. [10].…”

“…CuSbS 2 thin films have been synthesized by various techniques such as electro-deposition [4,9], magnetron sputtering [10], spin coating [11e13], spray pyrolysis [14], single-source thermal evaporation [15,16], thermal diffusion [17,18], chemical bath deposition [19], etc. However, there are only a few reports on the solar cells with CuSbS 2 absorber.…”

AgSbS2 and Ag3SbS3 absorber materials for photovoltaic applications

“…The higher value of 'a' shows that the material can be used as good absorbing material for solar cell application [1,9]. The result is comparable to the earlier reports on AgSbS 2 by W.C. Yang et al [1] CuSbS 2 by Bo Yang et al [12], Adam W. Welch et al [11] and Sn-Sb 2 S 3 by S. Mushtaq et al [10]. The type of optical transition can be explained by observing the dependence of the absorption coefficient, a on the photon energy, hn.…”

Earth abundant CuSbS2 thin films solution processed from thiol–amine mixtures

“…23 We calculated a hole mobility of µ h = 64.6 cm 2 V -1 s -1 , which is one of the highest in the range of values reported in the literature for films of this material prepared by other techniques, further corroborating that the films are comprised of high quality crystalline CuSbS 2 . 22,23,27,28 Such electronic characteristics, combined with the near--ideal optical band gap, high absorption coefficient, and the ability to easily tune film thickness through deposition of multiple coats, suggests that CuSbS 2 thin films deposited using this method would be suitable as absorber layers in photovoltaic devices. In summary, we have shown that the thiol--amine solvent system can be used to easily solution process phase--pure CuSbS 2 starting from bulk Cu 2 S and Sb 2 S 3 .…”