Effects of copper content and sulphurisation temperature on crystal structure, electrical and optical properties of spray pyrolyzed Cu2FeSnS4 thin films

Abstract

The fact that non-renewable energy resources are fast depleting have caused a resurgence of interest in photovoltaics. However, current materials used for solar cells such as CuInxGa(1-x)Se and CdTe consists of elements that are either scarce, costly or toxic. Hence earth abundant, non-toxic and low-cost materials are as alternatives are of considerable interest. One such material, Cu2ZnSnS4 (CZTS) have been studied and had shown positive results and yielded high efficiencies. Our focus in this project is to investigate the suitability of Cu2FeSnS4 (CFTS) thin film and how the variations in copper content and sulphurisation temperature can affect the morphology, crystal structure, electrical and optical properties of the material so as to improve its suitability as a candidate for the absorber layer of solar cell.

Different stoichiometric ratios of the novel earth abundant material, Cu2FeSnS4 (CFTS) - Cu1.6FeSnS4 (Cu-poor), Cu2.0FeSnS4 (stoichiometric) and Cu2.4FeSnS4 (Cu-rich) were synthesized using a simple spray pyrolysis technique under different sulphurisation temperatures at 400 °C, 500°C and 600°C using a non-toxic water based precursor. The synthesised thin films were then put through a series of characterisation – Secondary Electron Imaging (SEI), X-ray Diffraction (XRD), Raman Spectroscopy, Absorption Spectroscopy, and Hall measurement.

Analysis of data from characterisation techniques showed that higher sulphurisation temperatures (600°C) have positive effects and produced thin films with relatively large grains, have optical band gaps of 1.33 eV ~ 1.38 eV and carrier mobility and concentration were comparable to that of CZTS.

CFTS synthesised at 600°C has proved to be a promising material as photovoltaic absorber due to its close-to-ideal band gap, high crystallinity and similarity of electrical properties to CZTS. Its ease and cost of fabrication would present a significant leap for large scale commercial applications in photovoltaics.