Two novel methods for evaluating the performance of OTFT gas sensors

Two methods were proposed to evaluate the performance of organic thin film transistor (OTFT) gas sensors. A back-gated OTFT gas sensor with poly(3-hexylthiophene) (P3HT)/zinc oxide (ZnO) nanorods composite films as the active layer and gas sensing layers were prepared for nitrogen dioxide (NO2) detection. The electrical parameters of OTFTs based on pure P3HT film and P3HT/ZnO-nanorods composite films were calculated and analyzed. The response characteristics of gas sensor to NO2 were studied. It can be found that the response of OTFT gas sensor was inaccurate according to conventional definition. The effects of humidity and temperature on the response of sensors were evaluated. However, OTFT, as a multiparameter sensor, can provide more information to evaluate the gas sensing properties. The variation of Vth of OTFT gas sensor was associated with the content of ZnO-nanorods and the concentration of NO2. The variation mechanism of Vth was analyzed as well. The results indicated the variation of Vth as the response of sensor was reliable. The variation of Vth was attributed to the impact introduced by NO2 molecules on the charge carrier motion. In addition, the slope of fitting line (ΔI versus log t) was proposed as a new method to evaluate the gas properties of OTFT sensors. The calculated results illustrated that the sensitivity can be magnified compared to the variation of Vth and increased 40.2% due to appropriate amount of ZnO-nanorods doping.