Ex situ Sn diffusion: a well-suited technique for enhancing the photovoltaic properties of a SnS absorber layer

Sn atoms were thermally diffused into tin (II) sulfide (SnS) films prepared using chemical spray pyrolysis. This was achieved by depositing a layer of Sn metal over SnS films followed by annealing of the Sn/SnS bilayer films at 100 °C in high vacuum for 30 min. There was no contamination due to the formation of additional phases of Sn compounds up to a very high percentage of Sn diffusion. Contamination due to Sn–O–S phase was removed by Sn diffusion. The samples were optimized to achieve higher photosensitivity and low resistivity. All these enhanced properties were obtained without altering the optimum band gap of the SnS film which is suitable for maximum photovoltaic conversion efficiency.