Study on the structural, optical and dielectric properties of lead tin sulphide nanocrystals

In this work, a study was done on the structural, optical and dielectric properties of lead tin sulphide (PbSnS) nanocrystals and their thin films, which have got wide range of applications in photovoltaic systems. The nanocrystals of PbSnS were prepared by employing colloidal synthesis technique in which cubic PbSnS were obtained apart from the commonly found orthorhombic form. Nanocrystals of 5.84 nm were obtained which had a high band gap of 3.76 eV and Urbach energy of 0.163 eV. Almost 100% transmittance in the wavelength range of 300-800 nm was found. Nanocrystal thin films of PbSnS were prepared using successive ionic layer adsorption and reaction (SILAR) technique. The preparation of thin film samples by varying the amounts of complexing agent has been investigated. By varying the amount of complexing agents, the crystalline phase changed from cubic to orthorhombic. The lattice strain and dislocation density were found to be lower for the cubic phase. All the samples had high absorption coefficient in the ultraviolet region confirming that the thin films were composed of nanocrystals. There was an increase in transmittance from 60% to 80% with the increase of complexing agent. All the samples had high band gap, high refractive index and large surface roughness which make these PbSnS nanocrystal thin films suitable materials for window layer of solar cells. The cubic and mixed phase structured thin films behaved as polar dielectrics which can find potential applications in the design of efficient capacitors too.