In the current study, 1 m thick Cadmium Telluride (CdTe) coatings on glass substrate were created using thermal evaporation procedures (at temperature about 150 °C). The produced films were doped by ion exchange with Cu by submerging them in a solution of Cu(NO3)2 (1g/1000ml) for 30 minutes. Additionally, for the diffusion of the dopant Cu content, the doped films were annealed in vacuum for 60 minutes at various temperatures (RT, 100, 200, 300, 400, and 500 °C). The initial treatment mix was defined by the (EDAX). Cu was present in an average concentration of 10±2% at.% throughout all treated films, which was essentially constant. The structural characteristics for the untreated and treated films (lattice strain and crystallite size) were calculated using the XRD pattern. Swanepoel's method was used to determine the film thickness and refractive index of films. Experimental observations of transmission and reflection in a high absorption region were used to calculate the films' energy gap. The transmittance and reflection spectrum in the high absorption area were used to measure the optical band gap. The conceivable transition in these as-deposited and as-treated films is found to permit a direct transition with a band gap reduction from 1.50 at room temperature to 1.29 at 300 °C with a rise in temperature. After 300, the energy gap reverses its direction and increases. Crystallize size and lattice strain changes can both be used to explain changes in optical characteristics. For optoelectronic devices, Cu/CdTe films are recommended due to the optical constants' turnability.