Due to climate change and the need to use renewable energy resources, solar cell modification is being considered by scientists around the world. Photocatalytic and anti-reflective coatings on solar cells can affect the efficiency and stability of solar cells. In this study, single-layer zinc oxide thin films and double-layer ZnO–TiO2 thin films were investigated to study their photocatalytic and optical properties. In fact, the effect of porosity and the application of double-layer thin films on the optical and photocatalytic properties of coated glass were studied. Mesoporous thin films thinner than 100 nm were synthesized using a sol-gel process and the ZnO thin film with 2 × 10-2 M pore-forming agent (CTAB) in the coating solution had the highest transparency and ultraviolet absorption, and the ZnO thin film with 4 × 10-2 M pore-forming agent had the best antireflection performance. The double-layer thin film consisted of dense (interlayer) and mesoporous (top layer) ZnO layers had the best anti-reflection performance. It reduced the reflection of the glass substrate by 2.05%. Investigation of the effect of the coating thickness on optical properties showed that higher film thickness can lead to a shift of the visible wavelength with the highest transparency such that the increase of withdrawal speed from 1 mm/s to 5 mm/s resulted in an increase of this wavelength from 530 nm to 590 nm. The photocatalytic studies of the ZnO double-layer coatings showed that 120 min of ultraviolet irradiation could completely recover the transparency of the samples contaminated with fatty acid.