Simultaneous Optimization Of Charge-carrier Mobility And Fluorescence Quantum Efficiency By Controlling The Orientation Of F8BT Nanostructures

Conjugated polymers have attracted significant attention due to its excellent properties such as easy processing,low cost and flexible characteristics.Generally,the polymer films prepared by solution method often shows randomly orientation,while the orientation behavior of polymer is closely related to the electrical and optical properties of polymer materials.Therefore,controlling the orientation of polymers is an effective mean to optimize the physical and chemical properties of polymer.A number of reports have been reported to improve the electrical or optical properties of polymers by modulating polymer orientation,but most reports focus only on the effects of orientation changes on one aspect properties(electrical or optical)of the polymer.It is still a challenge both in science and application fields to simultaneous optimize the electrical and optical properties of polymer.Trace to its cause,it is contradictory to simultaneously increase the charge transport and optical properties of the polymer.When the high charge carrier mobility was achieved by ?-? interaction of the conjugated polymer,the quench exciton luminescence may also occurred.The purpose of simultaneously improving the electrical and optical properties of the polymer can be achieved by designing its molecular structure rationally,but the process is tedious and inefficient,thus,few research reports have been reported.Although it is difficult,it is vital to increase the carrier mobility and fluorescence quantum efficiency of the polymer in the fields of photoelectric device such as field effect light-emitting transistors and semiconductor pump lasers.Therefore,we attempted to solve the problems by controlling the orientation of the polymer.The research of this thesis is mainly divided into the following three parts:(1)Poly(9,9-dinoctylfluorenealt-benzothiadiazole)(F8BT)was chosen as the research object,and toluene was selected as the solvent of F8BT.In order to improve the performance of organic field effect transistor devices,before the F8BT thin film was prepared as the active layer,the silicon substrate was modified by OTS to form a dense and ordered monolayer hydrophobic interface,and the insulating layer/active layer interface was successfully modified.(2)A two-dimensional constrained space was constructed by nanoimprinting,and the surface morphology of the nanoimprinted thin film was observed by AFM test.The crystallinity and orientation of F8BT polymer in different confined space sizes were studied by one-dimensional X-ray diffraction and polarized light microscopy.It is found that the crystallinity and orientation degree of F8BT polymer gradually decrease with the increase of space-limited size.The maximum crystallinity and orientation degree are 0.81 and 0.79 respectively,which is achieved in the samples when the nanoribbon width is 85 nm.(3)We studied the effects of nanoconfined conditions on the electrical and optical properties of F8BT polymer.It is found that the carrier mobility and fluorescence quantum efficiency of nano-imprinted F8BT polymer were significantly improved compared with F8BT film.Next,we studied the effects of different spatially nanoconfined sizes on the electrical and optical properties of F8BT polymer,It is found that the carrier mobility of the OFET prepared by nanoimprinted F8BT thin film and the fluorescence quantum efficiency of F8BT thin film were simultaneously increase as the decrease of the width of the nanoribbon.The carrier mobility and fluorescence quantum efficiency are 0.826*10-3 cm2/(V·s)and 54.2%respectively when the nanoribbon width is 85nm,which is 2.6 times and 1.39 times of flat film.The crystallinity and orientation degree of the F8BT thin film increase as the decrease of nanoconfined size,resulting the reduction of traps density.Therefore,the carrier mobility and fluorescence quantum efficiency of F8BT polymer were improved simultaneously.