In this present work, we synthesized Copper Oxide (CuO) thin films by sol-gel method assisted by spin coating technique at room temperature. Variations of parameters used in this work are calcination temperature variations and application of the annealing treatment process to samples. Chemical characterization and crystal phase using FTIR and XRD were carried out to confirm the presence of chemical bonds and determine the crystal size and phase of CuO. The optical properties of the obtained thin films were characterized using a UV-Vis Spectrophotometer with a light spectrum range between 350 - 800 nm. The optical test results have succeeded in obtaining estimates of the optical band gap and Urbach energy of the thin film. The calculated band gap and Urbach energy for the spin time variation sample is 1.13 - 1.84 eV and 0.43 - 0.61 eV, respectively. While the calcination temperature variation sample's band gap and Urbach energy varies from 1.65-2.57 eV and 0.16 - 0.29 eV, respectively. Furthermore, the annealing treatment process on the CuO thin film significantly affects the regularity of the elements in the thin film. For the subsequent development, this CuO thin film will then be used as a tandem of Barium Titanate (BaTiO3) for solar cells.