Thermally evaporated SnS:Cu thin films for solar cells

Cu-doped SnS films with a thickness of about 300 nm have been grown on glass substrates by thermal evaporation technique. Different Cu-doped SnS films were obtained by controlling the Cu evaporation time to roughly alter Cu-doping concentration in SnS films (from 5.7 atom% to 23 atom% ). Then they were annealed at a temperature of 250°C and a pressure of 5.0×10^-3 Pa for 90 min. The structural, optical and electrical properties of the films were characterized with X-ray diffraction, UV/VIS/NIR Spectrometer and Hall Effect Measurement System. All the films are polycrystalline SnS with orthorhombic structure, and the crystallites in the films are all exclusively oriented along the (111) direction. With the increase of Cu-doping concentration, the evaluated direct band gap E_g of the SnS:Cu films initially decreases, reaches a minimum value of 1.38 eV with 15 atom% Cu and then increases thereafter. The carrier concentration of the films increases sharply, while the resistivity of the films decreases straightly. All the films are of p-type conductivity. Using the optimized conditions it is possible to prepare SnS:Cu thin films suitable for absorbers of thin film solar cells.