Effect of molybdenum (Mo) Doping on the structural, optical, and optoelectronic properties of zirconium sulphide (ZrS) nanostructures

Abstract

This study presents the electrochemical synthesis and characterization of molybdenum (Mo) doped zirconium sulphide (ZrS) thin films synthesized on fluorine-doped tin oxide (FTO) substrate for possible optoelectronic applications. Thin films of undoped ZrS and Mo-doped ZrS were synthesized via an electrochemical deposition method using Zirconium (IV) oxychloride octahydrate (ZrOCl 2 .8H 2 O), and ammonium molybdate (NH 4 ) 6 Mo 7 O 24 .4H 2 O at different concentrations (0.01, 0.02, and 0.03 mol) by applying an electrode voltage of 10 V at a pH of 5.6 and room temperature. The results showed that the transmittance value increases with the increase in Mo dopant percentage, which reflects the higher transparency of the doped thin film. The optical bandgap also increased with dopant concentration, suggesting bandgap widening due to impurity state formation. The XRD results showed that the films were crystalline in nature, where the diffraction peak values were 23.5941°, 34.9137°, 48.4287°, and 62.6298° for the pristine (ZrS). The crystallite size of the pristine films was in the range of 7.0076–8.0295 nm, compared to that of Mo-doped, which was reduced to 1.5963–1.7244 nm as a result of molybdenum incorporation, causing lattice strain and structural distortion arising from differences in size and valency of ions with the host crystal lattice. This hindered crystal growth, hence preventing the formation of large crystallites. The reduced crystallite size also suggests a solubility limit effect, where excess Mo generated structural defects that increased nucleation sites while restricting grain growth, resulting in smaller crystallites. The existence of the Zr, S, and Mo elements was evident from the SEM/EDX results. Electrical studies showed that film thickness increased slightly from 121.32 nm (pristine) to 124.05 nm (0.03 mol Mo). Also, the resistivity of the films was reduced to 2.36 × 10⁶ Ω·m (pristine) and 1.84 × 10⁶ Ω·m (0.03 mol Mo), which was followed by an increment in the conductivity from 4.34 × 105 S/m −1 (pristine) to 5.43 × 10⁵ S/m −1 (0.03 mol). Conclusively, Mo doping significantly enhances the optical and electrical properties of ZrS thin films, making them suitable for applications in solar cells, photodetectors, and other optoelectronic devices.