| Organic field-effect transistor（OFET）is considered to be the basic component for next generation electronic device due to its inherent advantages,including mechanical flexibility,light weight,low-temperature processing and low-cost production.Thus the development of high performance OFET is very important and urgent.To achieve high performance OFET,reasonable modification of device architecture is an effective route.On this standpoint,heterojunction OFET consisted of two organic layers has been well covered due to great conductivity.However,in most cases,despite of the enhancement of on-state current and field-effect mobility in organic heterojunction OFET,the off-state current at no gate bias often exhibits high value with the threshold voltage shift.Therefore,the current control of such heterojunction structure OFET should be further investigated.In this thesis,the SiO2 based OFET with isotype heterojunction consisted of p-type dioctylbenzothienobenzothiophene（C8BTBT）and pentacene have been fabricated.In such C8BTBT/pentacene isotype heterojunction OFET,we also confirm the two roles of pentacene which deposits upon C8BTBT.One is the energy step role for facilitating carrier transmission from Cu to C8BTBT.Furthermore,by comparing with the devices when the pentacene full-covered or part-covered C8BTBT,the second transport channel forming from pentacene/C8BTBT heterojunction has been proved.Our results show that C8BTBT/pentacene isotype heterojunction not only improves the performance of OFET effectively,but also exhibits a negligible heterojunction effect,which make the off-state current be controlled easily,even current on/off ratio can reach to 105.On this basis,in consideration of the most of modulated charges lie within 10 nm in the semiconductor near the insulators surface when OFET works in accumulation regime,the insulator property plays an important role in influence on the electric characteristics of OFET.However,SiO2 with rough surface can traps carriers easily,which would produce the adverse effect on devices.Therefore,several classic polymers with low surface roughness could be considered to utilized as insulator or modification layer to further improve device performance.Especially for SiO2/Poly（4-vinylphenol）（PVP）,SiO2/Polystyrene（PS）and SiO2/Polymethylmethacrylate（PMMA）,in our experiment,the double-layer insulators are carefully manufactured by spin coating technique to investigate the mechanism and interaction between insulators and C8BTBT/pentacene heterojunction.Moreover,it is meaningful to invest how the first and the second semiconductor layers change accordingly in the heterojunction OFET and whether the performance could be improved when the polymers are inserted between SiO2 layer and active layer.Our results show that SiO2/PS not only possesses evolved interface property but also further facilitates the growth of the C8BTBT and upper pentacene film at once,which leads the heterojunction OFET to achieve the highest mobility with 3.6 cm2/Vs.Therefore,the C8BTBT OFET with cheaper electrodes to achieve high mobility may benefit for the practical apllication. |
