Preparation And Characteristics Research Of Flexible Organic Thin Film Transistor Gas Sensor

Over the past few years,gas sensors with different structures?such as resistance,field effect transistor?FET?,quartz crystal microbalance?QCM?,etc.?have emerged Among them,organic thin-film transistors?OTFTs?have attracted great attention because of their light quality,low fabrication cost,and compatibility with a wide range of applications such as in sensors,smart cards,display backplane and so on.Benefiting from the enhanced sensitivity and multi-parameter measurement capability?including charge carrier mobility,on/off current ratio,threshold voltage,etc.?,OTFTs have taken an important place in the field of gas-sensing applications.In general,OTFT gas sensors were fabricated on glass or silicon substrates,which could not be stretched or bent and further applied for the wearable electronics.Meanwhile,vacuum evaporation technology was commonly adopted for the preparation of OTFTs,which increased the complexity and expense of fabrication process.Therefore,OTFT gas sensors with good flexibility,low cost as well as excellent gas-sensing properties are highly desired.In this work,flexible OTFT gas sensors were fabricated on PEN substrates coated with conductive indium tin oxide?ITO?film by solution processing methods to detect nitrogen dioxide?NO₂?at room temperature.The main contents of the research are as follow:1.Flexible NO₂ gas sensors based on organic thin-film transistors?OTFTs?were developed in this work,in which poly methyl methacrylate?PMMA?was spin-coated on PEN substrates with ITO electrodes as the gate dielectric layer and poly?3-hexylthiophene??P3HT?was spray-deposited as the active layer.The influences of PMMA solution concentration,spraying volume of P3HT solution,and bending cycles on electrical and sensing performances of flexible OTFT gas sensors were investigated.The results showed that the optimized flexible OTFT?the P3HT spray volume is 1 ml and the PMMA solution is 30 mg/ml?exhibited high field-effect mobility(9.51×10^-3 cm²/Vs at a gate bias of-50 V),high sensitivity(up to 0.169 ppm^-1),good repeatability and selectivity.Under the tensile stress??=0.23%?,the response of the optimized device constantly decreases from 12.90 to 1.32 after 500 cycles of bending,thus further work should be done for improving the flexibility of the sensor.2.Flexible OTFT gas sensors based on bilayer film and composite film were fabricated to detect NO₂,in which the film composed of P3HT and graphene?G?was spray-deposited as the active layer.The influences of film thickness and mass ratio of P3HT-G composite film,film structure,and bending cycles on electrical and gas-sensing performances of flexible OTFT gas sensors were investigated.The results showed that the device based on bilayer film has better electrical performance,while the device based on composite film has better gas-sensing performance.Graphene has high specific surface area,therefore,the response of graphene doped devices to NO₂ was improved.The composite film device with best gas-sensing performance presented good repeatability and a sensitivity of 0.0609 ppm^-1,in which the mass ratio of P3HT and graphene is 240:1,and the spray volume is 1 ml.Under the tensile stress??=0.23%?,its response decreased by 20 percent after 500 cycles of bending.Compared with undoped devices,its mechanical flexibility has been improved.This study provides an approach to fabricate flexible OTFT gas sensors with low cost and high performance,which might be expected to be integrated into wearable devices to detect ambient air quality.