| Organic semiconductor crystalline thin film has attracted tremendous attention because of long-range ordering,few defects,high crystal quality and outstanding optoelectronic properties.However,in the process of preparing crystalline organic semiconductor thin films,the growth of thin film tends to present a three-dimensional mode,resulting in high contact resistance and low preparation efficiency,which is not conducive to apply in large-scale,low cost devices.Aiming at these critical problems,the following works have been carried out in this thesis:1.Fabricating Controllable Large-area C10-BTBT Crystalline Film with 2D Growth Mode by Suppressing "Coffee-ring" EffectIn order to suppress the "coffee-ring" effect,wafer-level crystalline thin film with two-dimensional growth mode is successfully fabricated by blending small organic semiconductors with polymers,their applications in high-performance field effect transistors(FETs)are demonstrated.Firstly,the relationship between growth mode and solution concentration was investigated by atomic force microscopy(AFM).Then,the change of growth mode with or without polymer is revealed by computational fluid dynamics(CFD).CFD results show the convection velocity of fluid induced by solution evaporation decreased by 2.5 times after the introduction of polymer,which enhances the two-dimensional layered molecular stacking.Then,the evolution process of thin film formation under different solution concentration was investigated.When the blended solution of 2,7-didecyl[1]benzothiophene[3,2-b][l]benzothiophene(C10-BTBT)/polystyrene is used,the wafer-scale C10-BTBT crystalline thin films with few layers are fabricated by blade-coating method.The filed-effect transistor based on the crystalline film has a hole mobility up to 14.2 cm2 V-1 s-1,the current on/off ratio is over 107,the threshold voltage is 0.34 V,the sub-threshold swing is less than 1.03 V dec-1,and an average hole mobility of 9.3 cm2 V-1 s-1 for 36 devices on the same substrate.The performance of these FET devices has reached the best level reported in the literature.The fabrication of two-dimensional organic crystalline thin film with wafer-scale and high-performance field effect transistors successfully lays a foundation for the application in large-area high-performance integrated devices.2.N2 Airflow Induced Growth of Two-Dimensional C8-BTBT Crystalline Arrays Film Rapidly with High-Performance Organic Field-Effect TransistorsLarge area(maximum size is 1 ×1.5 cm2)organic crystal arrays film is fabricated by nitrogen flow guided method,and the fabrication efficiency was improved.In this method,a mixture of 2,7-dioctyl[1]benzothiophene[3.2-b][1]benzothiophene(C8-BTBT)and polystyrene was used to prepare crystalline films by nitrogen flow guided process.By optimizing the preparation conditions such as the molecular weight of polymer,the concentration of polymer solution and the nitrogen flow rate,the FET performance is promoted substantially.The results show that the molecular weight of polymer has a decisive influence on the FET performance.The high or low concentration of the polymer solution will affect crystalline quality of the film.The fast flow rate of nitrogen will cause the solution to fail to crystallize and the slow flow rate will cause the material to accumulate transversely to diminish the device performance.When the polymer concentration is 10 mg mL-1 and the nitrogen flow velocity is 200 kPa,the filed effect transistor based on the two-dimensional C8-BTBT crystalline film has a maximum hole carrier mobility of 21.7 cm2 V-1 s-1,and the average mobility of 49 devices on the same substrate is over 12 cm2 V-1 s-1,the curreit switching ratio is greater than 10-7,and the sub-threshold swing is as low as 1.23 V dec-1.In addition,this method is not only compatible with large area roll-to-roll fabrication process,but also has high fabrication efficiency,which provides a new strategy for large area rapid fabrication of high-performance organic crystalline film. |
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