Potential Effect on the Properties of Cu3BiS3 Thin Film Co-electrodeposited in Aqueous Solution Enriched Using DFT Calculation

In order to optimize the potential (U) to allow the synthesis of Cu3BiS3 (CBS) thin films by co-electrodeposition, the synthesized samples on fluorine-doped tin oxide (FTO) were sulfurized and then analyzed by many techniques. For U = −0.95 V, x-ray diffraction (XRD) shows the major presence of Cu3BiS3 characteristic peaks at 31.27°, 28.99°, and 34.81° as well as the main peak at 280 cm−1 in their Raman spectra. However, the potential decrease to U = −1.05 V introduced a broadening of the main peaks on the two XRD and Raman spectra. With regard to the morphology, scanning electron microscopy (SEM) mapping analysis shows a well-defined grain shape for U = −0.95 V, which varies with the variation in U. In addition, the UV–visible spectrum indicates that the optical band gap decreases from 1.44 eV to 1.33 eV when the potential U varies from −1.050 V to −0.950 V. The CBS semiconductor nature was also highlighted by the theoretical DFT calculations in the generalized gradient approximation with modified Becke–Johnson (GGA + mbJ) condition. This theoretical enrichment confirms that the CBS optical band gap is about 1.42–1.52 eV, which is comparable to that of the experimental study.