Effects of ammonia concentration on morphology, composition and optical properties of ZnO_1-xS_x thin films of Cu(In, Ga)Se₂ solar cells

Abstract

ZnO_1-xS_x films were prepared by chemical bath deposition (CBD) on glass substrate. The effects of ammonia concentration on the structure characteristics of ZnO_1-xS_x films were studied. The results of scanning electron microscope (SEM) show that the film has good density when the concentration of ammonia is 0.4 M. Because more S^2- ions are involved in the reaction and less precipitates are generated, the film is relatively dense. The distribution of the film element shows that the growth rate of the film first accelerates and then slows down as the concentration of ammonia increases. X-ray diffraction (XRD) study shows that the diffraction peak is obvious when the ammonia concentration is 0.4 M, and the crystallinity of the film is good. Ultraviolet (UV) spectrophotometer test results show that the ratio of S content (x) and optical band gap (E_g) satisfies E_g(x)=3.325 7x²−2.718 7x+4.357 6. Increasing S content can increase the optical band gap of the film, and increasing ammonia concentration can improve the absorbance of the film, but both have good transmittance. At the ammonia concentration of 0.4 M, the absorbance of the film is good in the wavelength range of 300–900 nm, the transmission rate reaches 80%, and the band gap is 3.75 eV, which is suitable for the buffer layer of solar cells.