Effect of Cu-doping on structural, optical and photoluminescence properties of CdS thin films

Undoped and Cu doped CdS thin films (Cd1−xCuxS, x = 0, 0.02, 0.04, 0.06 and 0.08) have been deposited on glass substrate by chemical bath deposition (CBD) method at 80 °C from aqueous solution. Crystalline phases and optical absorption of the films have been well characterized by X-ray diffraction and UV–visible spectrophotometer. Elemental composition of the Cd1−xCuxS films was studied by the energy dispersive X-ray (EDX) analysis. The optical absorption and transmission studies revealed that Cd1−xCuxS films had direct allowed transition with band gap energy increased from 2.18 to 2.34 eV. The average crystalline size was calculated from X-ray line broadening and it is decreased from 3.09 nm (CdS) to 2.81 nm (Cd0.96Cu0.04S) then started to increase which was confirmed by SEM studies. The substitution of Cu concentrations into the CdS lattice is confirmed by the change in lattice parameters, FTIR and photoluminescence studies. The observed lower crystal size (2.81 nm) and higher energy gap (2.28 eV) of Cd0.96Cu0.04S thin film is useful to design a suitable window material in fabrication for solar cells. The observed shift in both blue band and green band of photoluminescence spectra confirmed the substitution of Cu into CdS lattice.