Modulation of the Pb/Sn ratio in Pb1-xSnxS thin films synthesized by chemical solution deposition

Abstract This work presents the development of a formulation for the synthesis of Pb1-xSnxS thin films by chemical bath deposition. The success of this formulation is due to the high miscibility between lead sulfide (PbS) and tin (II) sulfide (SnS). By adding different concentrations of a Pb2+ ions solution to a Sn2+ S2− formulation, we obtain Pb1-xSnxS films with different Pb/Sn ratio. The presence of Pb2+ in those films is confirmed by X-ray energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). Structural analysis by X-ray diffraction (XDR) shows a crystalline phase change from an SnS orthorhombic structure (00.00 mmol Pb2+) to a solid solution where the orthorhombic and cubic structures coexist (30.00 mmol Pb2+), and finally reaching the formation of a cubic PbS structure. Changes in the morphology of the films are observed together with the incorporation of Pb2+ ions in the films, reducing the size of nano-flakes and becoming a more compact layer, leading to a decrease in the film thickness from 370 nm (00.00 mmol Pb2+) to 96 nm (50.00 mmol Pb2+). The decrease of the energy band gap (Eg) of the samples from 1.92 to 1.38 eV with the increase of the Pb2+ concentration is also observed, obtaining wide absorption spectra from visible to near-infrared.