Study Of Inkjet Printing Method For Perovskite Quantum Dot Films

The excellent optoelectronic properties of inorganic perovskite quantum dot materials have shown great potential for application in the field of display illumination.As a mature thin film micromachining technology,inkjet printing technology has outstanding performance in the field of industrial automation,for example in the field of organic light emitting diodes(OLEDs).The key technical problems of inorganic perovskite quantum dots can be solved as soon as possible,and the industrialization of QLED can be realized in advance.However,the research on the preparation of perovskite quantum dot light-emitting diodes by inkjet printing technology has just started,and there are still many problems.On the one hand,due to the instability of the perovskite quantum dots themselves,on the other hand,the complexity of the changes in physicochemical properties during the evaporation of ink during inkjet printing droplets has not been determined.Based on the basic principles of fluid mechanics and the principle of liquid molecular diffusion,for the specific experiments of inkjet printing of perovskite quantum dots,through the combination of theory and experiment,this paper mainly made a series of technical improvements,and continuously analyzed and summarized the effect of affecting the film formation of inkjet printing ink,and proposed the corresponding law.The specific work and research results of the thesis are as follows:(1)The effects of various factors on the morphology and morphology of the "coffee ring" in perovskite quantum dot film inkjet printing were studied in detail.First,a perovskite ink solvent capable of forming a stable ink jet is screened by theoretical calculation.One of the elements to achieve stable inkjet is viscosity.Based on the equipment currently used,the viscosity of the perovskite quantum dot ink can be between 1 cP and 10 cP to form a stable ink.However,the formed "coffee ring" destroys the uniformity of the film and affects the luminescence of the quantum dots,which is a key difficulty that must be solved.In the experiment,the effects of different single solvents on inorganic perovskite quantum dot inks were investigated,and one of the more suitable solvent dodecane(DOE)was selected.Secondly,experimental research was carried out on the number of droplets,ink contact angle,material concentration,droplet spacing,substrate surface free energy and droplet size at the same position,and the film formation properties were investigated,exploring its influence on the film formation of thin films.The results show that the accumulation of the number of inkjet printing droplets does not improve the "coffee ring" effect,only the magnification;The contact angle of the solution on the substrate directly affects the width of the inkjet printing dot film or the line film.The smaller the solvent polarity,the smaller the contact angle with the substrate,and the easier to form a wider film;The inorganic perovskite quantum dot ink with a larger concentration is more likely to form a printed film having a narrower line width;Different thicknesses and uniformity of the film are formed by different droplet spacings,and when the droplet spacing is between one-third and one-quarter of the spreading diameter,a better line film structure can be formed.On a low surface free energy substrate,a relatively uniform film can be obtained,while on a high surface free energy substrate,a "coffee ring" phenomenon is more easily formed.When the diameter of the droplet is too large,it will be affected by gravity during flight and evaporation.The combination of gravity and capillary force will further form a "coffee ring" structure.(2)The mechanism of action of the solvent in the perovskite quantum dot film inkjet printing process was studied,and the mixed solvent formulation which eliminated the "coffee ring" effect was optimized.The experimental results show that the polarity of the solvent should not be too large or too small.When the polarity is too large,the quantum dots decompose and annihilate.When too small,the quantum dots are precipitated and precipitated.When selecting a mixed solvent,not only the characteristics of the inorganic perovskite quantum dots themselves,but also the physical and chemical changes in the process of droplet evaporation and evaporation are considered,as well as the characteristics of the Marangoni flow phenomenon in the "coffee ring" effect,a mixed solvent formulation of dodecane and toluene was optimized to obtain a uniform and dense film,eliminating the "coffee ring" effect.