​A well-prepared ZnO and (Cd–Ni) co-doped ZnO thin films are synthesized using the simple, inexpensive sol–gel method by immersing technique. The optical, structural, and morphological characterizations of (Cd–Ni) co-doped ZnO thin films are performed by employing UV–Vis spectrophotometry, X-ray diffraction (XRD), and the scanning electron microscope (SEM). The XRD patterns are consistent with those for standard hexagonal wurtzite structure. As the content of (Cd–Ni) co-dopant is increased from 0 to 8%, the transmittance spectra () of thin films is decreased from 89 to 53%. In contrast, the reflectance spectra () is increase from 7.8 to 18.2%. The values of the optical band gap  are found between 3.09 and 3.28 eV depending on the (Cd–Ni) co-doping ratio. A combination of Wemple–DiDomenico, Sellmeier, Spitzer-Fan models as well Drude model are implemented to estimate different …​