Application Of Electrochemical Polymerization Luminescent Films In Organic Light-emitting Display And Their Basic Issues

Electrochemical polymerization(EP)has been proven to be an efficient method for the preparation of electro-active and conducting polymer films.In the EP method,the precursors are electrochemically oxidized or reduced,and the coupling reaction between the monomers occurs at the electrode interface with the deposition of the polymer film.Compared to other technologies,electrochemical polymerization method has several advantages including: 1.the synthesis and deposition of polymer are completed in one step;2.EP films can be selectively deposited on electrodes with preferred orientation by controlling the signal,which endows it with the ability to deposit patterned films without a mask;3.the thickness and dopant of the deposited films can be precisely controlled by the electrochemical polymerization parameters;4.EP films can be cost-efficient fabrication in terms of both materials and equipment,and the their preparation are environmentally friendly.Electrochemical polymerization is usually used for the synthesis of polymer with conductivity and has become an important method for the synthesis of conductive polymers.Electrochemically-assisted synthesis has become an important method for organic synthesis chemistry due to its simple process and non-pollution.Electrochemical synthesis was reviewed as a hot topic in the field of chemistry by the American Chemical Society in 2017.The use of electrochemical polymerization to prepare high-efficiency luminescent thin films is an important finding of our group and has successfully realized high-efficiency organic light-emitting diode(OLED).This technology for OLED display have much potential to develop into a brand new method for the preparation of color pattern films without vacuum and mask,which provides a new manufacturing solution for low-cost OLED display.This is a groundbreaking and new technology area,and exists huge challenges.The key issues including: 1.How to further improve the efficiency of OLED? 2.How to improve the quality of the EP films on microelectrode? 3.How to dock with the existing OLED backplane technology? This paper mainly focuses on some basic issues of application of electrochemical polymerization luminescent films in OLED display,and carries out the following research:Firstly,we research on the method of interface modification aiming at improving the quality of EP films and device performance.It was found that the ultra-thin gold nano-particles(AuNPs)layer modified on the electrode interface can repair the defects on the ITO electrode surface,improve the wettability of the ITO electrode,electrochemical redox reversibility,and the work function of the electrode surface.The ITO electrode modified with AuNPs exhibited a significant catalytic effect on the polymerization of the electropolymerized monomer(OCBzC)and accelerated the reaction rate.On the one hand,AuNPs can be act as the nucleation sites for the deposition of EP films,and induced a rapid and uniform growth of EP films.On the other hand,the oxidation potential of the OCBz C monomer can be reduced,and the reaction reversibility,diffusion rate and the electron transfer rate can be increased,thereby resulted in an increasing growth rate of the film and low dopant.After modification of AuNPs on ITO surface,we obtained high-quality luminescent films with smooth and compact morphology,low dopant,and OLED devices with uniform emission.Secondly,we develop a novel colour pattern method for the preparation of RGB full-colour films without a vacuum or mask-TFT directed dye electrodeposition(TDDE).Currently,most OLED displays are active matrix OLED(AMOLED),in which each sub-pixel is drivied by a TFT driving circuit,however,the preparation of color display is very expensive(vacuum+mask).We try to use TFT driving circuit on the AMOLED backplane as a switch for electrochemical polymerization to achieve selective directional deposition of color light-emitting films.The circuit analysis showed that the potential signal required for electrochemical polymerization can still be maintained after pass the TFT drive circuit(including resistance,capacitance,etc.).After the modification of electrode surface,optimization of polymerization parameters and TFT conditions,we verified that TFT driving circuit can be used as a switch to control the “on” or “off” states of the EP process and directed the deposition of dye onto the selected pixels.Furthermore,by controlling the working states of TFTs and systematically changing the RGB precursors,colour patterned films with high quality and light-emitting matrices showing pure RGB chromaticity have been obtained.These provided a novel technology to realize the colorization of AMOLED displays without a vacuum or mask,and the continuous development of TDDE as a low-cost technology will help promote the market competitiveness of OLED products.Thirdly,we investigated the application of EP technology in high-resolution,full-color OLED display.The resolution of the display is determined by the size of the pixel.Limited by the mask,the minimum accuracy of current technology is about 15 ?m.Besides,the difficulty and cost of the display increase sharply with the increase of the resolution,making it difficult to apply to high resolution display such as AR(Augmented Reality)/VR(Virtual Reality).The preparation of EP films does not require a mask plate,which has great potential in the application of high resolution display.We found that when electropolymerization is carry out on a high-density array microelectrode,the EP film is more smooth and substantially eliminates the edge effect during the polymerization of discrete microelectrodes.This effect is related to the average diffusion and lays a foundation for the preparation of high-resolution patterned films.Benefit from the homogenization effect of the diffusion layer on array microelectrode and the optimization of the experimental conditions,high-quality light-emitting films with a resolution of 1693 ppi,2116 ppi,and 2822 ppi were prepared for the first time by EP method,which showed a smooth surface morphology,a very clear boundary and their high-resolution displays exhibited good emission and without any dark lines.Furthermore,by controlling the EP signal of different pixel electrodes and replacing the RGB electrolyte orderly,the RGB patterned EP luminescent films and their corresponding full-color OLED displays with pure RGB chromaticity were obtained,besides,there is no contamination between the deposition of different color films.These results showed the great advantages and potential of EP technology in high-resolution and full-color OLED displays.It also provides a simple and low-cost method for the preparation of color OLED displays,VR/AR and other high-resolution OLED displays.