Characterization of UV Photodetectors Using Agar Bio-Templated ZnO Nanospheres

In this study, agar, a natural polysaccharide extracted from red algae, was employed as a bio-template to synthesize ZnO nanomaterials via a hydrothermal method for ultraviolet (UV) photodetector applications. The introduction of agar effectively modulated the nucleation and growth behavior of ZnO, inducing a morphological transformation from vertically aligned nanorods to uniformly distributed nanospheres. SEM and EDS analyses confirmed that agar acted as an organic scaffold regulating the crystal morphology, while XRD results verified the retention of the hexagonal wurtzite phase with high crystallinity. Photoluminescence (PL) spectroscopy revealed that an agar concentration of 0.15 g (AGZnO150) produced a well-balanced near-band-edge and deep-level emission, indicating optimized defect density and excitonic recombination. The AGZnO150 based UV photodetector exhibited an exceptional ON/OFF ratio of 104 under 365 nm illumination (11.3 mW cm⁻²), outperforming pure ZnO and previously reported ZnO-based devices. Furthermore, the device demonstrated excellent repeatability, stability, and UV selectivity, with a UV/visible rejection ratio of 2.54. These findings highlight the effectiveness of agar as a green and sustainable bio-template for tailoring ZnO nanostructures and advancing high-performance, eco-friendly UV photodetection technologies.