Effects of deposition temperature on structural, optical and electrical properties of TEA complexed nanocrystalline films of PbS prepared from lead acetate with reduced concentration

A number of researchers have been synthesising thin films of PbS on glass substrates by reaction of 1 M CH₄N₂S with of 0.50 M Pb(CH₃COO)₂.3H₂O complexed by 1 M triethanolamine (TEA) at different deposition temperatures and reported various temperature dependent properties of the films. In our work, we followed the same recipe but reduced the concentration of Pb(CH₃COO)₂.3H₂O by 0.10 M. The pH of the bath was adjusted at 12. The deposition has been carried out at five different temperatures—30, 40, 50, 64 and 70 °C. We wish to study how structural, optical and electrical properties of the films prepared with reduced concentration of Pb(CH₃COO)₂.3H₂O change with temperature. We have observed that at 30 and 40 °C, no crystalline PbS phase was formed, only elemental S was detected. The PbS phase formation was noticed only from 50 °C. The elemental S has been subdued and the crystalline PbS phase formation has been enhanced with increase of temperature. The average crystallite sizes were determined from XRD by Debye–Scherrer formula, lattice constants from Nelson–Riley plot, band gaps by the derivative method and electrical conductivities from current–voltage characteristics. It has been found that with the increase of deposition temperature, the crystallite size increases, strain decreases, band gap reduces and conductivity improves. The average crystallite sizes were found 35.79, 42.51 and 42.67 nm at 50, 64 and 70 °C respectively. The band gaps for these three films were noted as 1.74, 1.67 and 1.66 eV respectively indicating blue-shift from the bulk value. The tail widths of localised states in the forbidden band were observed in the range of (0.70–0.76) eV. The strains in the films were ~10⁻³ and conductivities were ~10⁻⁷–10⁻⁶ (Ω cm)⁻¹.