¹ Department of Physics, College of Education for Pure Science (Ibn al-Haitham), University of Baghdad, Baghdad 10071, Iraq.

² Department of Physics, College of Science, University of Baghdad, P.O. Box 4732, Baghdad 10071, Iraq.

* Correspondence: eman.nasir@sc.uobaghdad.edu.iq

To improve the efficiency of CZTS-based solar cells, it is essential to address the limitations of these systems, such as structural defects, non-ideal band alignment, and high recombination rates. The incorporation of cadmium (Cd) into the CZTS structure is an effective approach to overcome these limitations. In this research, we investigated the effect of Cd content (x = 0.0, 0.5, and 1.0) on the structural, optical, and electrical properties of thermally evaporated thin Cu₂Cd_xZn_1-xSnS₄ films, which were synthesized from their fabricated alloys. The elemental stoichiometry of CCZTS alloys was verified using EDX analysis. The XRD patterns of CCZTS alloys and thin films confirm the presence of a pure tetragonal phase along the [112] direction. AFM analysis indicated the formation of nanograins in the thin films’ structure, and the grain size increased with increasing x-value. The results of UV/Vis spectroscopy revealed that the incorporation of Cd in the prepared thin films resulted in a reduction in the direct allowed band gap from 1.52 eV to 1.38 eV as the cadmium content increased from 0.1- 0.3, respectively. This trend suggests that the incorporation of cadmium affects the electronic band structure of the films, potentially by introducing additional states within the band gap or modifying the band edge. The optical energy gap is a key parameter for photovoltaic applications because it controls the photon energy that the material can absorb. Hall effect measurements showed that all CZTS thin films adopted p-type conductivity, meaning that holes are the majority carriers in these films. The introduction of cadmium did not alter the type of conductivity but increased the holes mobility of in proportion to the cadmium content. These outcomes positively affected the performance of the fabricated CCZTS-based HJ solar cells as their power conversion efficiency increased with increasing Cd content.