Influence Of Interface Modification On Organic Field Effect Transistors And Their Sensing Properties

As one of the most important part of organic electronics,Organic field-effect transistor?OFET?has attracted considerable attention since it was invented.Compared to inorganic field-effect transistors,OFET shows the advantage of low cost,mechanically flexibility,large area fabrication process,high compatibility,diversity of material design,high transparency.Meanwhile,as a hot issue in the research of sensitive electronics and sensing technology,OFET based sensors show widely application in artificial intelligence?AI?and internet of things?IOT?,which requires high electrical performance of OFET devices,especially its sensitivity,light,temperature and humidity stability.To overcome these limitations,my thesis work has focused on new device structures,doping functional materials and OFET based logic circuits.As a result,high performance OFET gas sensors were obtained,and humid-air-operable,NO₂-responsive logic circuit were also prepared.The main work includes the three following parts:1.OFET sensitivity based on p-n heterojunction were carefully studied.OFET with a heterojunction structure were fabricated,which include p type semiconducting materials of copper phthalocyanine?Cu Pc?and n type semiconducting materials of N,N?-Dioctyl-3,4,9,10-perylenedicarboximide?PTCDI-C8?.OFET based on PTCDI-C8 film with different thickness were investigated,and the gas sensing performance were also studied.OFET based on p-n heterojunction had one order of magnitude enhancement of sensitivity towards nitrogen dioxide?NO₂?.To further reveal the intrinsic reason of the sensitivity enhancement,the morphology of the p-n heterojunction was characterized by atom force microscopy?AFM?.2.Influence of the graphene oxide?GO?doping on the OFET sensitivity were carefully studied.OFET based on polymethyl methacrylate?PMMA?and GO blend dielectric layer were fabricated,and the sensing performance were characterized.The results show that OFET device based on PMMA/GO blend dielectric layer had two orders of magnitude enhancement towards 2 ppm ammonia?NH₃?,and the device can still work after being stored in the ambient air for 3 weeks.By using AFM,X-ray diffraction?XRD?,Fourier transform infrared spectroscopy?FTIR?,the morphology of the different layers,crystalline characteristic of the organic semiconductor,and the functional groups in the blend dielectric layer were carefully studied.Moreover,GO sheets were also doped into6,13-Bis?triisopropylsilylethynyl?pentacene?TIPS-pentacene?to form a blend organic semiconductor layer,the results show that the sensitivity of OFET device based on blend semiconductor layer towards NO₂ had one order of magnitude enhancement.The instinct reason for the sensitivity improvement were studied by AFM to see the morphology change of the blend semiconductor layer.3.Influence of the UV-ozone treatment on the sensing performance of OFET device and the logic circuit based on two different types of OFET device were studied.Polystyrene?PS?and poly?bisdodecylquaterthiophene??PQT-12?were chosen to fabricate the organic semiconductor layer,and the organic semiconductor layer was exposed to UV light.The functional groups induced by UV-ozone treatment showed great enhancement on the sensing performance towards 200 ppb NO₂.In the meantime,based on UV-ozone treated device and untreated device,humid-air stable logic circuits were fabricated.By using Vout as the parameter to detect the NO₂,the sensitivity of the logic circuit approach 25%towards 200 ppb NO₂.Moreover,the logic circuit showed almost no drift while working in the humid environment compared to the OFET device.And the Vout can be easily measured by a voltmeter,which could remove the need for complex equipment?semiconductor analyzer system?for the sensing test.In summary,to overcome the low sensitivity,poor humid stability and the high requirement of complex equipment,high performance OFET based sensors were obtained by using p-n heterojunction,doping functional materials,layer modification,employing logic circuits,which pave the way for the extensive applications in the in artificial intelligence and internet of things area.