Organic thin-film transistors (OTFTs) are miniaturized devices based upon the electronic responses of organic semiconductors. In comparison to their conventional inorganic counterparts, organic semiconductors are cheaper, can undergo reversible doping processes and may have electronic properties chiefly modulated by molecular engineering approaches. More recently, OTFTs have been designed as gas sensor devices, displaying remarkable performance for the detection of important target analytes, such as ammonia, nitrogen dioxide, hydrogen sulfide and volatile organic compounds (VOCs). The present manuscript provides a comprehensive review on the working principle of OTFTs for gas sensing, with concise descriptions of devices’ architectures and parameter extraction based upon a constant charge carrier mobility model. Then, it moves on with methods of device fabrication and physicochemical descriptions of the main organic semiconductors recently applied to gas sensors (i.e., since 2015 but emphasizing even more recent results). Finally, it describes the achievements of OTFTs in the detection of important gas pollutants alongside an outlook toward the future of this exciting technology.

Polyvinyl phenol with a cross-linker agent was demonstrated as a dielectric film and incorporated to a bottom gate organic transistor structure. Films were shown transparent to visible light, resistant to organic solvents and compatible with plasma etching to open vias. Only cross-linked films, however, withstood lithography in order to pattern bottom contact electrodes on top of the dielectric. Cross-linked films showed a dielectric constant of ca. 5, which is higher than polymethylmethacrylate and silicon oxide. The devices herein have potential to be applied in flexible sensor arrays from organic transistors.

In this work, poly(3, 4-ethylenedioxythiophene) blended to polystyrene sulfonate (PEDOT:PSS) and poly(3-hexylthiophene) composite with 1-(3-methoxycarbonyl)propyl-1-phenyl[6], [6]C61 (P3HT: PCBM) deposited by spin and blade coating were thoroughly investigated by optical, morphological, and structural characterization techniques targeting the improvement of organic solar cells (OSCs). Processing parameters as surface treatment, filtration, concentration, additives, and deposition speed were studied in order to optimize OSC performance. The hole transport layer by spin coating featured a thickness of ca. 50 nm, a roughness of 2 nm, and absorbance lower than 0.03. Deposition by blade coating reduced film thickness and roughness to approx. 20 nm and 1.5 nm, respectively. It also brought further down thin-film absorption in the visible spectrum. P3HT: PCBM thickness could be easily varied from 100 to 200 nm by both deposition techniques. Absorbance (maximum of 0.4) and XRD data demonstrated enhanced thin-film crystallinity for P3HT: PCBM spun from 26 mg/mL solutions. Semiconducting films by blade coating provided thicker films ${(> 140\ \text{nm})}$ and an even higher absorption (0.5 - 0.8) due to the p-type molecule. The next step is to integrate these films to flexible OSCs.