Electronic structure and optical properties of the Ag₃SbS₃ crystal: experimental and DFT studies

A high-quality Ag₃SbS₃ single crystal was grown by the Bridgman-Stockbarger method and its crystalline structure and homogeneity were investigated. The fundamental absorption edge of Ag₃SbS₃ was studied. The value of the band gap of the studied compound was obtained at the level of 1.91 eV at T = 300 K. The structural, electronic, and optical properties of the Ag₃SbS₃ crystal were considered within the framework of first-principles calculations using density functional theory (DFT). The structure of the crystal lattice was optimized and its closeness to the experimental one is shown. The band-energy structure of the crystal was calculated revealing that the crystal has a band gap of indirect type with E_g = 0.88 eV for GGA (0.35 eV for LDA). The origin of the energy bands in the crystal was clarified and the nature of the fundamental absorption edge was analyzed using the calculated density of electronic states. The dielectric function (real part ε₁(ω) and imaginary part ε₂(ω)) and absorption coefficient α(ω) were calculated for two independent directions in the crystal and compared with experimental data. The character and anisotropy of optical functions are analyzed. The high value of the absorption coefficient of the Ag₃SbS₃ crystal is shown, which makes it a promising material for use as an absorbing layer in photovoltaics.