Chemical bath deposition and comprehensive characterization of CdSxSe1-x solid solution films with tunable properties

This work explores a chemical bath deposition (CBD) route to fabricate cadmium sulfide-selenide (CdS x Se 1-x ) solid solution films with tunable composition and properties for optoelectronics. Theoretical calculations of the boundary conditions for the CdS and CdSe formation in the citrate-ammonia-thiourea-selenosulfate system were made. The boundary conditions of CdS x Se 1-x were defined by the overlap area between the constructed CdS and CdSe formation zones. Single-phase CdS x Se 1-x films were successfully deposited at a cadmium salt concentration of 0.005 mol/L and a thiourea concentration of 0.05 mol/L, with sodium selenosulfate concentrations varying from 0.001 to 0.025 mol/L, corresponding to (NH 2 ) 2 CS: Na 2 SeSO 3 molar ratios of 50 : 1, 20 : 1, 10 : 1, 5 : 1, and 2 : 1, as confirmed by XRD analysis. This resulted in a substitutional parameter x ranging from 0.30 to 0.84, as determined by XRF. The optical and morphological properties of CdS x Se 1-x films were investigated. Optical transmittance measurements revealed a bandgap variation from 1.94 to 2.52 eV. The films exhibited continuous surface coverage, with morphology strongly dependent on Na 2 SeSO 3 concentration and deposition time. These findings demonstrate that controlled CBD enables precise tuning of composition and optical properties, providing a platform for potential optoelectronic applications.