Design And Synthesis Of Organic-inorganic Composite Dielectric Materials For Low Driven Voltage Organic Thin Film Transistor Applications

With the gradual commercialization of various technologies,such as OLEDs,flexible displays,and radio frequency identification devices,the development of organic thin film transistors(OTFTs)has led to tremendous opportunities.In recent years,significant progress has been made in the exploration of semiconductor and dielectric materials,interface modification,development of new electrodes and substrates for OTFTs.In addition,various film preparation processes have been developed to realize improved device performance.However,the existing OTFTs still have fatal challenges,such as insufficient performance,high power consumption,and poor stability,which limit the practical applications of OTFTs.As one of the most important functional layers in OTFTs,dielectrics play an important role in device performance,driven-voltage and operational stability.Therefore,the development of novel dielectric materials with high-quality,easy-processing,low-cost is very crucial for the industrialization of OTFTs.In this thesis,high quality organic-inorganic composite dielectric materials are prepared by solution method.Based on the prepared dielectrics,OTFT devices exhibit excellent properties,such as outstanding performance,easy processing,low power consumption and improved operational stability.Major highlights of this thesis are as follows:1.Three kinds of high-k(8-16)composite dielectric materials are prepared by hybridizing polyvinyl alcohol and three polysilsesquioxane precursors,which were hydrolyzed with three different siloxanes via sol-gel method.Based on the novel composite dielectric materials,high quality films were prepared and their performance was systematically investigated.The obtained results indicate that the side chain groups of the siloxane molecule have an important influence on the dielectric constant of the composite dielectric materials,as well as the surface roughness,surface energy and electrical properties of the dielectric layer.2.Three kinds of OTFT devices with the driven voltage of as low as 3 V were fabricated,among which the devices with composite dielectric layer based on 3-chloropropyl trimethoxy silane exhibited the best performance in terms of mobility,threshold voltage,hysteresis and operational stability.Both,pentacene and C8-BTBT OTFTs based on the composite dielectric layer demonstrated extremely high mobility,in which the average mobility of the pentacene device was measured to be 5.7 cm~2/V·s,and the maximum mobility was 6.0 cm~2/V·s.While,the average mobility of C8-BTBT devices was as high as 28.5 cm~2/V·s,and the maximum mobility was up to 53 cm~2/V·s.Furthermore,in order to avoid the over evaluation of mobility,the mobility factor was estimated by the effective factor r,and the obtained results also confirmed the superiority of our fabricated devices in terms of mobility.The method for preparing organic-inorganic composite dielectric material explored in this work has the advantages of simple processing by utilizing easily available raw materials,low cost,excellent film-forming quality and facile preparation in large scale.Applying the composite dielectric material in OTFTs not only greatly reduced the driven voltage,and lowered energy consumption,but also impressively improved the overall performance of the fabricated devices.This work provides a novel concept for the research and application of dielectric materials in the field of OTFTs,and has important scientific significance.