Regulations of aging time on optical properties of nano-crystalline ZnO thin films fabricated by sol–gel method

Nano-crystalline Zinc oxide (ZnO) thin films on glass substrates have been fabricated by sol–gel method for different aging times. The thermal curve of the dried gel was examined and it was found that evaporation of solvent and the decomposition of the organics have completed before 250[Formula: see text]C. X-ray diffraction patterns and Atomic Force Microscope images of samples only have a small difference of microstructure. The transmittance spectra revealed high transmittance in visible region. The optical band gap of the samples remined stable (3.28[Formula: see text]eV). Also, the Urbach energy was calculated to explain the defect concentration. The Photoluminescence spectra in ultraviolet and visible regions were studied, and the decreased intensity of peaks at 387[Formula: see text]nm and the increased emissions in visible range were found. The results showed that excessive aging time can cause degeneration of optical properties of thin films.