Design,fabrication And Application Of RAFT Functional Polymers For Organic Thin Film Transistors Insulator Materials

In the past two decades,electronic products based on small organic molecules and conjugated polymers have been extensively studied,such as organic light-emitting diodes,organic solar cells and organic thin film transistors(OTFTs).Organic thin film transistors,as an important part of microelectronics technology,show extraordinary talents because of the applications in emerging electronic products such as integrated circuits,sensors and displays,etc.After decades of development,the field-effect mobility of organic thin film transistors has increased from 1.0×10^-5 cm²·V^-1·s^-1 to generally greater than 1.0 cm²·V^-1·s^-1,and can even be compared with single crystal silicon.Comparing with inorganic metal oxide transistors,organic thin film transistors also have some problems such as difficult controling of organic semiconductor crystals and higher threshold voltage.Therefore,in addition to the research of semiconductor materials,it is also important to develop insulating layer materials,which compatible with semiconductors,lead to superior device performance.Pentacene is remarkable because of its high mobility and the ability to form ordered films.It is well known that the charge transport properties of conjugated molecules,such as pentacene,are closely related to their crystal structure,degree of crystallinity and so on.Controlling and optimizing the quality of the film is essential to realize the application of pentacene devices,although the exact form of these correlations is not well understood,the difference in their orientation and grain size can significantly affect device performance.Therefore,we designed methyl methacrylate(MMA)as the main body,glycidyl methacrylate(GMA)as the cross-linking unit,and a benzene ring-containing monomer which is similar with pentacene as the functional unit.Through the increasing trend of aromaticity,increasing trend of functional unit content,and different polymerization methods to study its impact on pentacene thin film transistors.The first chapter of this article gives a brief introduction to organic thin film transistors,including its device structure,performance parameters,research progress and application areas.Also including the factors affecting the growth of pentacene,the growth pattern of pentacene and the research progress.Finally,the basic principles and characteristics of Reversible Addition-Fragmentation chain Transfer polymerization technology(RAFT)are introduced.In the second chapter,in order to study the regulation of p-pentacene thin film transistors with different aromatic properties of functional monomers,RAFT polymerization was used to synthesize copolymers,including MMA,GMA,benzyl methacrylate,methacrylate-1-naphthyl-ethyl ester,and Methacrylate-9-anthracyl-methyl ester.The results showed that the addition of functional units significantly improved the crystalline form of pentacene,from islands with smaller crystals to fish bones with larger crystals.With the increase of aromaticity,the better the device performance could be.And the highest carrier mobility is the device which containing the anthracene structure,it can reach 0.65 cm²·V^-1·s^-1,and the reliability factor is 84%.The third chapter of this article,based on the content of chapter two,further studys the regulation of pentacene crystals by the increasing trend of aromaticity and the increasing trend of functional unit content.RAFT polymerization was used to prepare Functional unit of block copolymers.And using these as a modified layer to deposit pentacene at their respective optimum temperatures to construct devices.The results show that the more similar the structure of the modified layer material to pentacene,the better the device performance could be.The moderate content of functional units contain,the better the device performance could be.Compared with random copolymerization,block polymers can self-assemble more effectively,making it more compatible with pentacene,thereby changing the properties of the interfacial property.The dielectric constant increases from4.14 for random copolymers to 6.59 for block polymers,and the threshold voltage changes from-15 V which based on random copolymers has dropped to-7 V which based on block polymers.The mobility of devices which based on PMG-co-NEA3(0.16 cm²·V^-1·s^-1)increased to the one of devices which based on PMG-b-NEA3(0.34 cm²·V^-1·s^-1)as the same composition.