SnS absorber thin films by co-evaporation: Optimization of the growth rate and influence of the annealing

Tin sulfide thin films were prepared by co-evaporation on soda-lime glass substrates, for use as absorber layers. The synthesis was carried out at 350 °C substrate temperature and varying the growth rate in the 2-6 Å/s range, adjusting the deposition time in order to obtain thicknesses in the 700-1500 nm range. After evaporation, the samples were heated at 400 °C and 500 °C under various atmospheres. The evolution of the morphological, structural and optical properties has been analyzed as a function of the thickness and deposition rate, before and after annealing. For the samples grown at the lowest rate, SnS and Sn2S3 phase mixing has been observed by X-ray diffraction. Samples with reduced thickness preferably crystallize in the SnS phase, whereas thicker layers become richer in the Sn2S3 phase. The sulfur treatment of samples prepared at the lowest rate results in the formation of SnS2 phase. Otherwise, the samples obtained at the highest rates show single-phase SnS after heating at 400 °C in sulfur atmosphere, with gap energy values around 1.24 eV.