Iron Chalcogenide Thin Film Deposition for Solar Absorbers

Interest in the Fe$_{2}$-IV-VI$_{4}$ system stems from a desire to fundamentally change the approach to thin-film inorganic solar absorbers by synthesizing and studying new flat-band d-element chalcogenides. Impetus for the work is provided by the band gap (Eg = 0.9 eV), excellent optical absorption ($\alpha >$ 10$^{5 }$cm$^{- 1})$, and minority electron transport properties (300 cm$^{2}$/V-s) of FeS2 (pyrite). Fermi level pinning, however, results in a low open circuit voltage (Voc) limiting the absorber potential of FeS$_{2}$. The olivines Fe$_{2}$SiS$_{4}$ and Fe$_{2}$GeS$_{4}$ are promising candidates for realizing the desired properties. Fe$_{2}$GeS$_{4}$ thin films are fabricated via RF sputtering and demonstrate a band gap of 1.5 eV with an optical absorption $\alpha $ $>$ 10$^{5 }$cm$^{-1}$ at Eg +1 eV. These ternaries provide a new entry point for development of highly efficient thin-film solar absorbers.