Engineering of Structural Phase Transition and Electrical Conductivity of Cadmium-Doped CZTS Films via the Direct Isometric Substitution

Doping CZTS (copper-zinc-tin-sulfide) by replacing zinc with cadmium atoms is a crucial process for improving its electrical and optical properties. The primary goal is to modify the bandgap and increase the electrical conductivity of the material to enhance its efficiency in solar cell applications. This substitution induces a phase transition in the crystal structure from kesterite (favorable for zinc) to stannite (stable for cadmium). Experimental results showed that the pure sample (x = 0) was unstable, with a large dispersion in the conductivity measurements. Adding cadmium at a low ratio (x = 0.01225) improved the stability of the measurements while the conductivity decreased to ~10 S/m due to distortion stress in the crystal lattice. Increasing the ratio to x = 0.0269 resulted in a dramatic jump in the conductivity (~56 S/m) which is an indication of the onset of the phase transition. A computer code based on the K-Means algorithm was used to analyze the dispersion of measurements and isolated the most statistically reliable group.