Cadmium-Doped ZnS Thin Films via SILAR for Buffer-Layer Applications: An Experimental and mBJ-DFT Study

Cd-doped ZnS thin films (0–6 at.%) were deposited by SILAR and assessed as buffer layers for thin-film solar cells. XRD shows a single zinc-blende phase, with a small lattice expansion after Cd incorporation. As the Cd content increases, transmittance decreases and the direct band gap narrows, pushing absorption further into the visible. DFT with mBJ reproduces this redshift and attributes it to Cd-related states near the band edges. Hall measurements indicate stronger n-type transport at higher Cd levels, with lower resistivity, higher mobility, and a larger electron concentration. Overall, about 6% Cd provides a workable balance between transparency, absorption, and conductivity, making ZnS:Cd a suitable buffer-layer candidate.