The Preparation Of Electrochemical Polymeric Films And Its Application In Organic Electronics

In recent years,organic light-emitting diodes?OLED?and corresponding display products have been widely launched in the market due to their unique advantages,such as wide viewing angle,wide color gamut,self luminous,fast response,low driving voltage,thin panel and flexible display.However,due to the low yield of OLED products prepared by vacuum mask evaporation which result in the relatively high price of OLED products,it is urgent and necessary to develop a low-cost and rapid OLED preparation method to promote OLED commercialization.Electrochemical polymerization is an effective and simple method for preparing electroactive conductive polymer films at room temperature and atmospheric pressure,which can effectively reduce the cost of materials and equipment.Our group have successfully developed a new method for the preparation of high-resolution full-color display devices by electrochemical polymerization.A small amount of red,green and blue light-emitting molecules are dissolved in the electrolyte solution and electrochemically coupled to sequentially prepare red,green and blue emitting layer on ITO pixel array substrates.This process doesn't need harsh conditions such as high vacuum and pixel alignment during vacuum mask evaporation,which is a new solution processing method with great application prospects.The introduction of hole injection/transport layers?HIL/HTL?and electron injection/transport layers?EIL/ETL?is an effective method for improving the performance of OLED devices.In solution processing devices,the main methods to achieve this goal are through reasonable choice of orthogonal solventsorthogonal solvent or the crosslinking treatment initiated by photo or thermal.Electrochemical polymerization shows unique advantages in the preparation of multi-layer highly cross-linked films.By electrochemical polymerization,the films themselves are highly cross-linked and insoluble in common organic solvents.Through reasonable control of the potential window of each layer,the next layer can be obtained by electropolymerization without destroying the upper electropolymerized layer.By rationally selecting the electropolymerized precursor molecules for each layer,different properties can be imparted to the layers.Theoretically,an OLED device can be completely prepared by the electrochemical method.Such a high-efficiency method for preparing multi-layered dense films for organic electroluminescent light-emitting devices will greatly promote the commercialization of the OLEDs.The dissertation centers on the preparation of electrochemical polymeric films and its application in organic electronics.It explores a new method for preparing highly crosslinked and lowly doped thin films,and conducts two-layer and three-layer electropolymerized organic electroluminescent devices,showing good performance,which can be used in the fabrication of display substrate.It mainly includes the following three aspects:Firstly,we regulated the viscosity of the electrolyte solution by adjusting the content of PC in the electrolyte solution,which could decrease the diffusion coefficient of the electrochemical polymerization,and then promote the quality of surface morphology,degree of crosslinking,and doping level of the electropolymerization film.A method has been developed for the electropolymerization of conjugated rigid small molecules such as TCTA into flat,dense,highly cross-linked,low-doped films.For TCTA,the good redox reversibility of its own triphenylamine confers the same good redox reversibility of TCTA EP film.The obtained TCTA EP film was used as a hole-transport layer for solution processing P-PPV?PLED?light-emitting device,showing that the TCTA EP film which had a higher crosslinking degree functioned best and was comparable to PEDOT:PSS.The 28 nm TCTA EP film device showed the best results when the light emitting layer became a small molecule OCBzC.Compared to the PEDOT:PSS device,the turn-on voltage reduced from 5.3 V to 3.9V;the maximum brightness increased from 6521 cd/m² to 7988 cd/m²;and the maximum current efficiency increased from 3.66 cd/A to 5.25 cd/A.Secondly,we used the prepared TCTA EP film as the hole transport layer for preparing the multilayer electropolymeried device.Through simple modification of ITO anode,the TCTA EP film improved the electro-polymerized OCBz C light-emitting layer quality,reduced the doping amount and improved the redox reversibility of the light-emitting layer?the ultra-high resolution display substrate was more apparent?,thereby enhancing the performance of the electropolymerized OCBz C emitting layer.The turn-on voltage of the two-layer electropolymerized organic electroluminescent devices reduced to 5.2 V,the maximum brightness was 3712 cd/m²,and the maximum current efficiency was 5.45 cd/A,which was 2.3 times that of the electropolymerized OCBzC device alone.On this basis,we replaced the vapor-deposited TPBi electron transport layer with an electropolymerized BzP2C4 thin film and built a three-layer electropolymerized organic electroluminescent devices.When the thickness of the electropolymerized Bz P2C4 film was 12 nm,the device performance reached best.The device showed turn-on voltage of 4.5 V,maximum brightness of 1206 cd m^-2,and maximum efficiency of 0.76 cd A^-1.Finally,we synthesised a new molecule TAT-6-Cz containing TAT core and six carbazole groups as electropolymerization coupling units.Due to the small amount of synthesis,it was impossible to thoroughly investigate the hole mobility of the electropolymerized thin film under the condition of aggregation.However,we have found that this electropolymerized TAT-6-Cz EP film had better tantalum capacitor properties.Cyclic voltammetry tests,AC impedance tests and galvanostatic charge and discharge tests showed that TAT-6-Cz EP film had good tantalum capacitor performance.When the charge-discharge current density was 20A/g,the maximum specific capacitance value of 294.8 F/g was obtained.When it was continuously charged and discharged at a current density of 20 A/g for many times,43.8%of the capacity could still be retained after 400 cycles.