Manufacturing process and optical properties of zinc oxide thin films as photoanode in DSSC

Purpose: It has been recently observed, that zinc oxide thin films are gaining much popularity, particularly in applications such as toxic gas sensors, photocatalytic materials and photovoltaic cells. Due to much better physical properties of ZnO compared to the ones of titanium dioxide (TiO₂), which is currently the most used material in dye sensitized solar cells, efforts are being made to fabricate DSSCs with thin films and/or nanostructures, including nanowires, nanofibres and nanoparticles of zinc oxide. Design/methodology/approach: In this paper, zinc oxide thin films were prepared using sol-gel and spin coating methods from Zn(COO)₂ × 2H₂O dissolved in ethanol and acetic acid with ZnO monocrystalline nanoparticles of 0 and 10% (wt.) relative to the final concentration of produced solutions. The effect of calcination process on ZnO thin films at 600°C were examined using atomic force microscope to investigate the morphology of semiconductor coatings, infrared spectroscopy to prove the chemical structure of material. Besides, optical properties were analysed on the basis of absorbance in the function of wavelength spectra and the values of energy band gaps were studied. Findings: The topography analysis of ZnO thin films showed an increase in roughness with the increase of zinc oxide nanoparticles in the thin films material. In addition, the analysis of the optical properties of ZnO thin films showed a decrease in absorption level in the range of near-ultraviolet wavelength for the obtained layers after annealing. Research limitations/implications: It was found that ZnO thin films produced by spin coating and calcination method are a proper material for photoanode in dye-sensitized solar cells, as zinc oxide layers provide better conductivity across the photovoltaic cell. Practical implications: The results provide the possibility of production DSSCs with zinc oxide thin films as photoanode. Originality/value: The dye-sensitized solar cells based on zinc oxide photoanodes could be alternative semiconductor material to titanium dioxide, which is used in nowadays solar cells. It was estimated that ZnO, especially zinc oxide nanostructures have much better physical properties, than TiO₂ structures. What is more, zinc oxide thin layers are characterized by the lower energy losses resulting from the physical properties of such nanostructures, which results in more efficient solar energy into electricity conversion.