Effect of thiourea concentration on the structural, optical and photoelectric properties of ZnO/ZnS/PVC composite films used as flexible UV photodetectors

In this work, a new design of flexible photodetectors based on ZnO/ZnS/PVC composite films was realized using polyvinyl chloride as the polymer substrate. ZnO/ZnS composites were successfully synthesized by a hydrothermal method using a mixture of zinc acetate and thiourea, resulting in the formation of microspheres with a core- shell structure. The effect of thiourea concentration as sulfur source (0.2, 0.4, and 0.6 M) on the physical properties of ZnO/ZnS composites was investigated. XRD patterns and FTIR spectra demonstrated a successful fabrication of ZnO and ZnS composites. In addition, the particle size, morphology, elemental composition and the bandgap energy of ZnO/ZnS were studied through the utilization of SEM, EDS and UV-visible spectrophotometer. Finally, the effect of thiourea on the performance of UV photodetectors based on ZnO/ZnS/PVC composite films was investigated using I–V characteristics under dark and UV light conditions. The results showed that the photodetection of the samples improved with increasing thiourea concentration. In particular, the UV photodetector based on PVC-ZSO-3 exhibits a higher photocurrent (2.55 nA), responsivity (0.187 µA/W) and detectivity (5.18 × 10⁶ Jones) than other samples. This gives the impression that the polymer as an insulating material has a promising future as a flexible photodetector worth exploiting.