PVA Treated PEDOT-PSS: TiO2 Nanocomposite Based High-Performance Sensors Towards Detection of Relative Humidity and Soil Moisture Content for Agricultural Applications

In this work, we authors report the investigation of polyvinyl alcohol (PVA) modified poly(3,4-ethylene-dioxythiophene)-poly(styrene sulfonate) (PEDOT-PSS): titanium dioxide (TiO₂) nanocomposite sensors towards relative humidity and soil moisture measurements at room temperature for agricultural applications. The morphological and structural features of the nanocomposite films were studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infra-red spectroscopy (FTIR) and theromogravimetric analysis (TGA). These characterizations reveal the successful formation of nanocomposite structures with improved thermal stability. The conductivity of nanocomposite film shows significant improvement compared to pure PEDOT-PSS by three orders of magnitude. Sensitive layer of PEDOT-PSS:PVA doped TiO₂ thin films were fabricated on ITO substrate using the spin coating technique to study relative humidity and soil moisture response. The nanocomposite film was subjected to varying levels of relative humidity (%RH) ranging from 5 to 95% and varied moisture content in soils of Montmorillonite and Kaolinite at room temperature. The resistance was found to decrease with increasing RH and gravimetric moisture content in Montmorillonite and Kaolinite soils. The humidity sensing response of PEDOT-PSS: PVA doped TiO₂ (8 wt%) composite thin film shows higher sensitivity of 96% with fast response and recovery times of 10 and 50 s respectively. Further, the sensitivities of 10.5 and 8.32 kΩ with 0.2% variation in gravimetric water content were achieved upon exposure of the prepared sensor to red and black soils respectively. Due to being relatively inexpensive, simple fabrication technique, excellent sensitivity, good repeatability and reproducibility these PVA modified PEDOT-PSS: TiO₂ nanocomposites sensors could be potentially useful in quantification of soil moisture content and relative humidity for agricultural applications.