Enhanced multifunctionality of SnO2 and W-doped SnO2 thin films synthesized via ultrasonic spray pyrolysis: applications in UV photodetectors, photocatalysis, and tunable surface hydrophilicity

Abstract

SnO₂, Sn_1-xW_xO [2, 5, 10 at.%] thin films were synthesised using the ultrasonic spray pyrolysis. Structural analysis revealed that W doping significantly improved crystallinity and modified the morphology of SnO₂ thin films, with 5% W doping resulting in the most uniform grain growth and optimal structural properties. In contrast, excessive doping at 10% induced lattice distortions and particle agglomeration. Fourier transform infrared spectroscopy (FTIR) analysis highlighted intensified O–H and H–O–H vibrational modes with increasing W content, indicating enhanced surface hydroxylation, which is crucial for optical and catalytic applications. The optical bandgap widened from 3.63 eV for pristine SnO₂ to 3.84 eV for 2% W-SnO₂ and stabilized around 3.82–3.83 eV for 5% and 10% W-SnO₂. Thermoelectric studies revealed improved electrical conductivity at 5% W doping due to an increased carrier concentration of 2.49 × 10¹⁸ cm⁻³. Notably, the Seebeck coefficient (│S│) showed partial recovery at 10% doping, suggesting a nuanced balance between carrier density and scattering mechanisms. For photodetection, the 5%-W-doped SnO₂ demonstrated a markedly enhanced Ultraviolet response, with significantly higher peak currents during UV exposure. Photocatalytic experiments showed superior performance for the 5% W-SnO₂ film, achieving 98% methylene blue degradation under Ultraviolet light within 150 min. Furthermore, contact angle measurements revealed a transition from hydrophilicity to hydrophobicity. The water contact angle increased from hydrophilic behaviour in pure SnO₂ to highly hydrophobic surfaces at 10% W doping. This change underscores the tunable surface properties of W-doped SnO₂ thin films. These findings establish them as promising candidates for multifunctional applications in optoelectronics, photocatalysis, and surface engineering.