Effect of tin concentration on the structural, optical and thermoelectric properties of CZTS thin films gown by chemical solution method

In this work, we have modulated the structural, morphological, optical and thermoelectric properties of CZTS thin films (TFs) by controlling the concentration of tin atoms. The CZTS TFs were grown by simple chemical solution method by changing tin mole concentration from 0.5 mM to 2.0 mM (labeled as T1, T2, T3 and T4). XRD data have revealed the formation of best crystalline CZTS TF at 1.5 mM tin concentration because tin (Sn+4) atoms are placed its own lattice sites therefore achieved the best crystal quality of CZTS. Furthermore, the phase purity of CZTS TF was confirmed by Raman spectroscopy. The lattice vibration of CZTS TF were observed at 329 and 334 cm−1 with A1g mode and 367 cm−1 with B(TO) mode. The strongest Raman CZTS vibrational mode was observed for sample T3 which supported our XRD data. SEM images demonstrated that the surface of grown CZTS thin films became smoother with increasing the mole concentration of tin atoms up to 1.5 mM because the density of CuS grains has minimum value for this sample. The optimum band gap of T1, T2, T3 and T4 samples was estimated to 2.23, 2.15, 1.91 and 1.82 eV respectively which also confirmed that sample T3 has band gap value very close to reported value. The Seebeck coefficient, electrical conductivity and power factor values were enhanced from (243–762 μV/°C), (21–152 S/cm) and (1.24 × 10−4- 8.82 × 10−2Wm−1K−2) with increasing the mole concentration of tin (0.5–1.5 mM) at measurement temperature 100 °C.