Development of nanostructured Cu3SnS4 thin films through annealing of the stack of precursors for photonic applications

Abstract

The Cu/Sn/S stack was obtained at room temperature by the thermal evaporation technique at vacuum ~ 2 x 10^− 4 Pa using sequentially evaporated layer deposition (SELD) technique on corning 2947 substrate. The as-deposited stack was regrown to provide Cu₃SnS₄ (CTS) phase on annealing at temperatures varying from 623 to 723 K for one hour in vacuum level ~ 2 x 10^− 1 Pa. The as-deposited stack exhibits amorphous behaviour, whereas films grown at annealing temperature (T_A) from 623–723 K attain nanostructured Cu₃SnS₄ phases. The influences of annealing temperature on the characteristics of these films were investigated by analyzing their structural, morphological, compositional, optical, and electrical behaviour using analytical characterization techniques. The annealed films of CTS crystallize in a tetragonal crystal system and provide a space group of 42m [121]. The grown films provide granular-type structures, and the particles grown at 673 K show an increased size. The bandgap (E_g) of films decreases from 2.13 to 1.78 eV, and their absorption coefficient (α) > 10 ⁵ cm^− 1. The low resistivity of 9.37 x10^− 3 Ω-cm, high mobility of 56.4 cm²/V-s, and acceptor concentration of 1.19 x10¹⁹ cm³ at 673 K result from an increased crystallite size, which reduces grain boundary scattering. Cu₃SnS₄ is a promising absorber layer for thin-film solar cells, known for its tunable bandgap, high optical absorption, low cost, and use of earth-abundant elements.