Impact of Annealing Temperature on Hydrothermally Synthesized Copper Antimony Oxide (Cu2Sb2O) from Amorphous Phase to Monoclinic Structure

In this study, a hydrothermal approach has been employed for the synthesis of copper antimony oxide films. Cu2Sb2O exhibits an amorphous phase prior to annealing and a polycrystalline phase (monoclinic structure) after annealing at temperatures ranging from 200 to 400oC, as showed by the XRD. The angles of 26.934o, 34.228o, and 38.362o correspond to the diffraction peaks (111), (211), and (311). High annealing temperature caused the film's lattice to reform and crystalize, which could cause cell ignition. The diffraction angles of the peaks moved higher because it was assumed that the annealing process affected the material. The unannealed Cu2Sb2O material displays small nanoparticles and a noteworthy nanoflake structure. Under different annealing temperatures, the nanoparticle's size increases when the film surface is ignited at higher pressure. When nanoparticle clusters were present during annealing, the material's surface energy increased. The absorption spectra displayed a consistent high rate of absorption between 200 to 600 nm, but showed a considerable decline beyond this range, with the minimum point noted between 700 to 850 nm. Yet it increased again between 980 and 1100 nm wavelength range. Light absorption is high in Cu2Sb2O, specifically in ultraviolet and blue regions. The film's absorbance increased from 0.145 to 0.185 a.u. when Cu2Sb2O was annealed at 200 °C. An increase in temperature from 200 to 400 °C caused an improvement in Cu2Sb2O's absorbance because of its susceptibility to temperature. The low reflectance of the films in both areas makes them ideal for both solar and photovoltaic cells. As the annealing temperature increased from 200 to 400 °C, the synthesized Cu2Sb2O film's bandgap energy decreased from 1.78 eV to a range of 1.66–1.21 eV.