Structural, morphological and optical characterization of chemically deposited Cu2O/PbS thin films

Abstract

Cu2O/PbS core-shell thin films were synthesized by a chemical bath deposition technique using a reactive mixture containing copper nitrate, lead nitrate, ethylenediaminetetraacetic acid, tetraethyl amine and ammonia solution. Their structural and optical properties are reported in this work. For the elemental composition estimation, Rutherford backscattering spectroscopy (RBS) was performed. From the proton induced scan on the substrate containing the films, all the elements that make up the films were extracted as Cu (34.86%), Pb (1.69%), S (42.31%) and O (65.15%). This is an indication that Cu2O-PbS quaternary thin films were actually deposited on the substrate. The X-ray diffraction analysis showed the formation of multiple peaks indicating that the films possess polycrystalline structure. The scanning electron micrographs of the films depicted particles of different sizes scattered across the film surface. The absorbance, transmittance, absorption coefficient, band gap and extinction coefficient were modified by thermal annealing. Absorbance varies from 1.175 to 1.35 for as-grown, 1.475 to 1.50 for annealed at 150 oC and 1.65 to 2.00 for annealed at 200 oC. The percentage transmittance of 6.75 % was obtained for as-grown sample while those of the annealed samples are 6.0 % and 5.0 % at 150 oC and 200 oC respectively. Maximum absorption coefficient values are 3.48 x 106 m -1 , 3.68 x 106 m -1 and 4.60 x 106 m -1 for As-grown, annealed at 150 oC and 200 oC respectively. The band gap energy value is found to increase from 3.50 eV to 4.00 eV as a result of the increase in annealing temperature from 150 oC – 200 oC. Extinction coefficient values generally varies from 0.75 to 2.70 for as-grown, 0.80 to 2.85 for annealed at 150oC and 0.85 to 3.00 for annealed at 200oC. Based on the wide band gap exhibited by the films, it can be concluded that the films are suitable as window materials in the fabrication of solar cell devices.