Fabrication and comprehensive experimental evaluation of surfactant-activated PEDOT:PSS/SnO2 thin films deposited via spin coating for advanced sensing applications

Abstract

Abstract This research investigates the fabrication of surfactant-mixed tin oxide (SnO2) nanostructured thin films on a fluorine-doped tin oxide (FTO) substrate via hydrothermal synthesis, focusing on their structural, morphological, optical, and electrical properties for sensor applications. To examine the effect of surfactant concentration, cetyltrimethylammonium bromide (CTAB) was incorporated at varying weight percentages (0%, 6%, 11%, 16%, and 20%), resulting in five distinct sensor samples, labelled SnO-1, SnO-2, SnO-3, SnO-4, and SnO-5, respectively. X-Ray Diffraction (XRD) analysis confirms a tunable crystallite size from 12.2 nm (SnO-1) to 4.8 nm (SnO-5), with a corresponding increase in defect density (0.0067 nm−2 to 0.0434 nm−2), making SnO-5 highly sensitive for gas sensing and humidity detection. Field Emission Scanning Electron Microscopy (FESEM) and Transmission Electron Microscopy (TEM) analyses reveal a structural transformation from aggregated grains in pure SnO2 to a highly interconnected, flower-like morphology in SnO-5, increasing surface area and enhancing adsorption properties. Brunauer–Emmett–Teller (BET) surface area measurements show a significant increase from 53.15 m2/g (SnO-1) to 132.70 m2/g (SnO-5), with pore volume rising from 0.245 cm3/g to 0.405 cm3/g, suggesting improved catalytic and electrochemical activity for energy storage and supercapacitors. Fourier Transform Infrared Spectroscopy (FT-IR) spectra confirm functional groups (O–H, C=O, O–Sn–O) essential for gas and biomolecular interactions, making the material suitable for biomedical and environmental monitoring applications. Optical studies via UV–Vis spectroscopy (Ultraviolet–Visible) indicate a tunable band gap correlating with surface modifications, beneficial for optoelectronic and UV sensor applications. Current–Voltage (J–V) measurements reveal a drastic reduction in cut-in voltage from 0.405 V (SnO-1) to 0.071 V (SnO-5), demonstrating superior charge transport, which is useful in resistive-type gas sensors and electronic devices. The Electro-chemical Impedance Spectroscopy (EIS) study further supports this by showing a lower charge transfer resistance (Rct = 1250 Ω) and increased inter-facial capacitance (Cit = 159.2 µF) in SnO-5, making it an excellent candidate for solid-state super capacitors and bio-sensing applications. These findings confirm that surfactant-modified SnO2 nanostructures are highly adaptable for gas sensing, environmental monitoring, biomedical applications, and energy storage technologies.

Keywords

• Hydrothermal synthesis
• Surfactant-mixed SnO2
• PEDOT:PSS (Poly(3,4-ethylenedioxythiophene): Poly(styrenesulfonate))
• X-ray diffraction
• Flower-like structure