Influence of Cu and Ag doping on structure and optical properties of In2O3 thin film prepared by spray pyrolysis

Thin films of In2O3 and In2O3 doped with Ag+ or Cu2+ were assembled by spray pyrolysis from aqueous solution at 450 °C. The microstructure analysis and optical properties were investigated using XRD, SEM, EDX and UV-Vis. spectrophotometer. XRD analysis proved that Ag-doping greatly reduces the crystallites sizes of In2O3 from 96 nm to 59 nm. However, Cu-doping has less pronounced effect on the crystallite sizes than that of Ag doping. The band gap energy of In2O3 decreases with both Cu2+ and Ag+ doping. The change in lattice parameter of cubic In2O3 with Cu and Ag substitutions is compatible with the ionic radius of the substituted ions, i.e. Ag-substitution increases the lattice parameter and Cu-substitution decreases the lattice parameter. The calculated direct band gap of bare In2O3 film is 3.59 eV. Doping In2O3 with Cu2+ and Ag+ decreases the band gap to 3.36 eV and 3.27 eV, respectively. Ag+ substitution in place of In3+ ion in In2O3 cubic lattice causes negative strain value due to the shrinkage of the interplaner spacing of the unit cell. In contrary, replacing In3+ cation with Cu2+ cation expands interplaner distances of the crystallographic planes of In2O3 lattice and causes positive strain value. The present work demonstrates the capability to assemble high quality doped - In2O3 thin films by simple solution based spray pyrolysis.