Co-evaporated Tin Sulfide Thin Films on Bare and Mo-coated Glass Substrates as Photovoltaic Absorber Layers

This work has been focused on the synthesis by co-evaporation on bare and Mo-coated glass substrates of tin sulfide films with thicknesses in the 700-1200 nm range for use as absorber layers, with a substrate temperature at 350 °C and a sulfur partial pressure of 1-2*10-3 Pa. After evaporation, the samples were heated at 500 °C under Ar atmosphere. The evolution of the morphological, structural, chemical and optical properties of the samples deposited on bare or Mo-coated glass substrates has been analyzed as a function of the thickness, before and after annealing. For the samples grown on bare glass, some phase mixing has been observed by X-ray diffraction (XRD). Samples with reduced thickness preferably crystallize in the SnS phase, whereas thicker layers crystallize in the Sn2S3 phase. Otherwise, the Mo-coated glass substrate favors the crystallinity in the phase SnS preferably. Scanning electron microscope (SEM) shows thin films with homogeneous and uniform surface. All samples were characterized by reflectance (R) and transmittance (T) measurements in the wavelength range 300-1500 nm, showing an increase of the maxima of reflectance when the films are obtained on bare glass and after annealing. The energy band gap values, calculated from optical measurements of T and R, are between 1.14-1.20 eV, being suitable for absorbers layers in photovoltaic applications.