Modulation of structural, optical and thermoelectric properties of sol-gel grown CZTS thin films by controlling the concentration of zinc

Abstract In this manuscript, we have demonstrated the effect of Zinc concentration on the structural, optical and thermoelectric properties of CZTS thin films (TFs) grown by sol-gel technique. We have deliberately changed the mole concentration of zinc from 0.5 to 2.0 mM (labeled as Z1, Z2, Z3 and Z4 respectively) to modulate the various properties. The XRD data demonstrated that Z2 sample with Zn concentration 1.0 mM has better structure with minimum number of secondary phases as compared to other samples because extra Zn atoms may create stress in the CZTS lattice. Raman spectroscopy measurements demonstrated that A1 mode of CZTS phases was observed at 334 cm−1 along with the presence of binary and ternary phases of Sulfide. It was also observed that Z2 sample has the strongest A1 Raman mode. The surface morphology of grown samples was observed using scanning electron microscope. The SEM images suggested that increasing Zinc concentration causes the surface rough. UV/Vis and photoluminescence spectroscopy results confirmed that sample Z2 has optimum value of band gap whereas Z1, Z3 and Z4 have band gap values deviated from experimentally reported value. Seebeck data depicts that sample Z2 has the lowest value of Seebeck coefficient. It may be explained as; Seebeck coefficient is strongly dependent upon the secondary phases and Z2 has minimum number of secondary phases, therefore lowest value is understandable.