Structural and optical properties of ZnO thin films prepared by spray pyrolysis on PI plastic substrates at various temperatures for integration in solar cell

Films of zinc oxide (ZnO) have been prepared by chemical spray pyrolysis by spraying a semiconductor precursor solution directly onto polyimide (PI) plastic substrates at different substrate temperatures, in the range of 250–295 °C in 15 °C steps. The influence of substrate temperature towards structural and optical properties of the obtained films was studied. XRD patterns showed that ZnO films are polycrystalline and with hexagonal structure. The crystallite size of the films increased as the film temperature does. The Raman lines around 436 and 575 cm −1 , were observed for all films. The optical energy gap for all thin films was calculated using Tauc’s equation. It was found that the band gap decreases as the substrate temperature increases, with energy values in the range of 3.45–3.25 eV, whereas transmittance enhances as the substrate temperature did. In particular, the high band gap and transmittance values of ZnO films prepared at 295 °C make these films a potential optical window material for CIGS multilayer solar cells.