The effect of the concentration of tin (Sn) in the metallic precursor, on the structure, morphology, optical and electrical properties of electrochemically deposited lead-tin-sulphide (PbSnS) thin films

Abstract

A study has been carried out to investigate the effect of the concentration of Sn in the metallic precursor on the structure, morphology, optical and electrical properties of PbSnS thin films. The films were directly electrodeposited on ITO-coated glass substrates using a 3-electrode electrochemical cell having graphite as the counter electrode and Ag/AgCl as the reference electrode. Several depositions were carried out, with each deposited film having a different concentration of Sn in the metallic precursor whilst all other parameters were kept constant for all the films. Post deposition annealing was carried out in air at 250 o C for an hour. A variety of techniques were used to characterize the films. Results showed that the increase in Sn concentration did not modify the structure and preferred orientation of the films. However, it caused a slight increase in the average grain size of the films and electrical conductivity. All the films showed direct transition with the optical band gap reducing with increasing Sn concentration. The refractive index of the films showed anomalous dispersion behaviour within the UV region, and normal dispersion in the visible and infrared regions, whilst following an increasing trend with the grain size. SEM image showed spherically shaped grains of different sizes distributed randomly with good coverage across the entire area of the substrate. The EDAX spectrum was consistent with formation of the ternary PbSnS compound on ITO-coated glass substrate. Overall results indicate that, the optical and electrical properties of the electrochemically deposited PbSnS thin films can be tuned to make them suitable for specific applications by varying the concentration of Sn in the metallic precursor.