The Effect Of Functional Layer Regulation Of Organic Thin-Film Transistors On Their Gas Sensing Properties

With the improvement of social productivity,a large number of toxic and harmful gases are inevitably discharged into the air,which will not only bring environmental and ecological problems but also seriously threaten human health.Therefore,the accurate detection of toxic and harmful gases is particularly important.In addition,gas sensors are also widely used in the fields of food safety,drug delivery,fire detection,and national defense security,bringing great application value to society.Compared with traditional inorganic sensors,organic thin-film transistor(OTFT)-based gas sensors have the advantages of low consumption,high selectivity,flexibility,and room-temperature operation,and thus become a research hotspot in this field.In the structure of OTFT,organic semiconductor(OSC)film is the main channel of OTFT carrier transmission and is easily affected by external factors,so it is the research focus of the OTFT-based gas sensor.At present,a large amount of research has focused on the design and synthesis of OSC molecules that have a specific response to gas analytes,but this scheme has a long design cycle,which increases the device fabrication cost.Therefore,based on these problems,this dissertation adopts the method of functional layer regulation to study its influence on OTFT gas sensing performance.This study is divided into the following three parts:1.Influence of solvent vapour annealing and vertical annealing processes on the microstructure of functional layer films and the performance of OTFT-based gas sensors were studied.Solvent vapour annealing can reorganize the OSC film.The morphology and microstructure of the OSC film can be effectively controlled by selecting different solvents.It was found that trimethylbenzene with a high boiling point could form a flat6,13-bis(triisopropylsilylethynyl)-pentacene(TIPS-pentacene)film with high crystallinity,and the mobility of OTFT based on this film was nearly 4 times higher than that before treatment.In addition,using toluene with a low boiling point as the solvent,TIPS-pentacene film with large grain boundary density was obtained.The increased grain boundary density enhanced the interaction between the film and gas,thus achieving a response of up to 524%,which was about 12 times higher than that before treatment.At the same time,its limit of detection(LOD)reached 148 ppb.A series of 6,13-bis(triisopropylsilylethynyl)-pentacene(TIPS-pentacene)thin films with fibrous ordered morphology were obtained by the vertical annealing process,and OTFTs with parallel and vertical structures were fabricated.For devices with parallel structure,the arrangement direction of their fibrous morphology is parallel with the direction of the conductive channel,which is conducive to the faster transmission of carriers away from the grain boundary,thus the mobility of OTFT is about 1.5 times higher than that of OTFT based on traditional annealing process.For devices with vertical structure,the arrangement direction of their fibrous morphology is vertical to the direction of the conductive channel,and carriers inevitably pass through the grain boundary during transmission.The interaction between the grain boundary and gas is the main working mechanism of OTFT gas sensors.Therefore,compared to devices fabricated using traditional annealing processes,the responsiveness of devices fabricated using vertical annealing processes to gas has increased by nearly 20 times.2.Influence of ultraviolet-ozone(UVO)treatment on the microstructure of functional films and the performance of OTFT-based gas sensors was studiedA series of OTFTs based on UVO-treated P3 HT thin films were prepared by controlling poly(3-hydroxylthiophene-2,5-diyl)(P3HT)thin films with different durations of UVO treatment.It was found that UVO treatment changed the microstructure of the P3 HT film and reconstructed the trap density of state(DOS)in the film.Trap DOS as a carrier trap can effectively enhance the interaction between the film and the gas.Therefore,the response of the optimized OTFT sensor to NO2 is 3112%,which is about43 times higher than that of the device without UVO treatment,and the LOD is as low as7.3 ppb.At the same time,the device has good stability,selectivity,and reuse characteristics.3.Preparation of bilayer functional films by a one-step method utilizing vertical phase separation effect and its influence on OTFT-based gas sensors were studied.The vertical phase separation effect of OSC/dielectric mixtures in the film-forming process enables the automatic layering of OSC and dielectric materials.Therefore,compared with the traditional layer-by-layer preparation route,the two-layer functional film can be prepared simply and efficiently by the one-step process.A series of OTFTs with different P3HT/poly(methyl methacrylate)(PMMA)mixing ratios were prepared by the one-step method using the vertical phase separation effect.The mixed bilayer film prepared by the one-step method has more P3HT/PMMA interfaces,which enhances the physical adsorption of the film to gases,thus obtaining enhanced gas sensitivity.The optimized device achieves response up to 1481%,which is about 13 times higher than the traditional two-step device,and obtains LOD as low as 0.7 ppb.In addition,the effects of PMMA with different molecular weights on the structure of the P3HT/PMMA mixed film were investigated,and the key role of the interface of the mixed material in gas sensing was further demonstrated.In summary,this dissertation explores the effect of functional layer regulation on the gas sensitivity of OTFT from many aspects,studies the annealing process,UVO treatment,one-step preparation process,and other functional layer regulation routes,explores gas sensing mechanisms including crystal boundary,trap DOS and mixed interface,provides new ideas to improve the performance of OTFT-based gas sensor,and lays a foundation for the preparation of high-performance OTFT-based gas sensor.