Synthesis and Evaluation of Optical and Morphological Studies of Cu2ZnSnS4, Cu2CoSnS4 and Cu2NiSnS4 Thin Films using Chemical Bath Deposition Method for Device Applications

Abstract

Sustainable energy generation and conversion using kestrite solar cells are at the forefront of photovoltaic research interests. kesterites of Cu₂ZnSnS₄, Cu₂NiSnS₄ and Cu₂CoSnS₄, thin films were prepared on glass substrates using chemical bath deposition. The result showed that the absorbance of the thin films varied from 0.3 to 0.7 spanning the entire UV-VIS-NIR regions. The films showed high absorbance at a wavelength of 200nm and decreased exponentially to 400nm and gradually increased with increase in wavelength. The transmittance varied from 0-2% for Cu₂CoSnS₄, 0-2.3% for Cu₂NiSnS4 and 0-2.2% for Cu₂ZnSnS₄. The bandgaps of the films; 1.20 eV- 1.30 eV for Co²⁺, 1.25 eV – 1.30 eV for Ni and 1.25eV-1.35eV for Zn²⁺ respectively.  It was noticed that Zn²⁺showed slight increase in the bandgap energies when compared to Co and Ni ion concentrations. Nevertheless, the ranges in the values of the energy gaps clearly showed that these thin films are very good materials for photovoltaic applications.Scanning electron micrographs result showed crystalline morphology for all the samples. The surface morphological study of Cu₂CoSnS₄, Cu₂NiSnS₄ and Cu₂ZnSnS₄ at (0.1M , 0.3M and 0.5M doping concentrations), showed that the grain size of all the samples are large and more oriented when doped with 0.5M and 0.3M concentration compared to that doped with 0.1M.