Effect of CoCl₂ Doping on the Optical and Electrical Properties of PEO Polymer Films for Optoelectronic Applications

Highly porous polymer films were synthesized using the solution casting technique by doping polyethylene oxide (PEO), a semi-crystalline polymer known for its good film-forming ability, chemical stability, ionic conductivity, and optical properties, with varying concentrations of cobaltous chloride (CoCl₂) (0, 5, 10, 15, and 20 wt%). CoCl₂, a transition metal halide containing Co²⁺ ions, is known for its tunable optical absorption, enhanced electrical conductivity, and strong coordination behavior, making it suitable for improving the performance of polymer matrices. X-ray Diffraction analysis revealed a gradual reduction in crystallinity with increased CoCl₂ content, indicating structural disruption and confirming (120) and (032) planes as per JCPDS standards. Fourier transform infrared (FTIR) spectra showed interactions between Co²⁺ ions and PEO ether groups, suggesting the formation of metal-ligand coordination bonds. UV-Visible spectroscopy exhibited a redshift in the absorption edge, and Tauc’s plots revealed decreasing direct and indirect band gaps. The extinction coefficient increased significantly (from 1×10⁴ to 6.7×10⁴), indicating enhanced light absorption and suitability for UV photodetector applications. AC conductivity increased with doping due to enhanced ion mobility, while Nyquist plots confirmed reduced bulk resistance and improved ion transport through hopping mechanisms. The 20 wt% CoCl₂-doped film exhibited a bulk resistance of just 33 Ω, indicating potential semiconductor or ionic conductor behavior. SEM images confirmed increased surface porosity and morphological changes, consistent with the semi-crystalline nature of the films. These findings suggest that CoCl₂-doped PEO films are promising candidates for flexible electronics, optoelectronic devices, sensors, and solid polymer electrolytes in energy storage applications.