Remarkable change of structural, optical, photoluminescence and electrical properties of chemically prepared nanocrystalline films of PbS with concentration of triethanolamine (TEA)

Abstract

Although triethanolamine (TEA) is widely used as complexing agent in the preparation of nanocrystalline PbS thin film by chemical bath deposition method, not enough studies have been reported on how its concentration affects various properties of the films. In the present work, we studied the effect of concentration of TEA on structural, morphological, optical, photoluminescence and electrical conduction properties of the films. We observed that with the increase of molar concentration of TEA—the crystallinity deteriorates with reduced crystallite size and increased strain and dislocation density; the densities of the films have been reduced; the films become non stoichiometric; optically these become more transparent but less reflecting showing prominent blue shift in the optical band gap which increased with the concentration of TEA; the width of the localized states in the band gap has been increased. The refractive index and extinction coefficient of the films are observed to be wavelength dispersive. The refractive index decreases with the increase of TEA complexation. In the NIR region, the extinction coefficient also decreases as concentration of TEA increases. The real and imaginary parts of dielectric constant replicates the refractive index and extinction coefficient curves respectively against wavelength. The PL spectra reveal conduction band to valence band transition with reduced intensity at higher molarity of TEA. The current–voltage measurement shows that the conductivity decreases considerably with the increase of TEA concentration. Our measurement estimated the crystallite size in the range of 29–37.49 nm, strain ~10−3, dislocation density ~1011 cm−2, band gap 0.8–1.55 eV, bandtail width 0.27–0.57 eV, the refractive index 2.3–5.8 and conductivity 0.0011–0.20 (Ωcm)−1.