Modulation And Enhancement Of Luminescence Performance Of Tri-color Quantum Dots In Color QLED Devices

In recent years,red,green,and blue quantum dot light-emitting diode devices（QLED）devices have outstanding performance in realizing full-color display devices due to their high color purity,high saturation,and wide color gamut.QLEDs with multi-layer thin film structures can be prepared by a full solution method,such as spin coating and inkjet printing.The preparation process is simple and low in cost,which is an important direction for the development of flat-panel color display devices in the future.Such a color flat panel display is usually composed of a combination of red,green,and blue QLED devices.Although the luminous efficiency,lifespan and other performance parameters of red,green,and blue QLEDs has greatly improved with the current technological progress,the luminous performance of QLEDs of different colors is not balanced.In flat panel display devices,the balance of red,green,and blue luminescence performance is the basic requirement for obtaining high-quality color image display.If the luminous performance of the red,green,and blue QLEDs is unbalanced,it is necessary to achieve a balanced color luminescence through electrical signal correction through a complex feedback circuit,which will complicate the circuit system and increase the cost of the flat panel display.Aiming at the problem of unbalanced luminescence performance of different color quantum dots in color QLED devices,the enhancement and balance regulation of red,green,and blue quantum dot luminescence performance for color QLED devices are studied.It is found that the mapping relationship between the preparation process parameters of red,green,and blue quantum dots and their luminescence properties,providing the basis for material design and preparation for the balanced regulation of the luminescence of tri-color quantum dots.Secondly,it is also explored that the carrier transport and recombination laws of different transport layers in red,green and blue QLED devices.It is proposed to comprehensively regulate the energy band structure of quantum dots and carrier transport layers to balance red,green,and blue QLEDs and improves the luminous efficiency.Finally,a technical solution to further enhance the luminous performance of red,green,and blue QLEDs using the surface plasmon enhancement effect of metal nanoparticles and quantum dots is proposed.The research content and innovations of this article are summarized as follows:（1）In order to obtain the color gamut required by the National Television Standards Committee（NTSC）of the United States and further expand the color gamut,the fluorescence emission peaks of tri-color quantum dots prepared in this paper are located at 620-640 nm（red light）,520-560 nm（green light）,460-470 nm（blue light）.And the FWHM is narrow,meeting the needs of wide color gamut display.In this paper,by studying the synthesis mechanism,the preparation process of red,green,and blue quantum dots is adjusted and optimized.And the correlation between process parameters and high-efficiency performance is established.The study finds that as the reaction time increases,the QY value first increases and then decreases.The ratio of reactants Zn:Cd,Se:S and OA greatly affects the wavelength positioning,QY and FWHM values.The lower the vacuum pressure of the reaction system before the inert gas is introduced,the shorter the heating time is,the QY value increases,and the FWHM decreases significantly.Finally,tri-color quantum dots with perfect crystal structure,uniform size,high stability and high fluorescence quantum yield are obtained through precise control of the reactant composition,concentration,reaction time,temperature,pressure,atmosphere and other parameters and the improvement of post-processing methods,which provides material preparation for the balanced regulation of the luminescence of the tri-color quantum dots.（2）The localized surface plasmon enhancement effect improves the luminescence performance of quantum dots.The localized surface plasmon enhancement effect of metal nanoparticles and quantum dots is used to improve the electroluminescence performance of QLED devices.Firstly,bifunctional molecules is selected as surface modifiers to study the correlation between the photoluminescence properties of quantum dots and the concentration of metal nanoparticles and the p H value of the solution.The experimental results show that with the increase of the concentration of gold nanoparticles,the PL intensity of the quantum dots first increases and then decreases,verifying the effect of the plasmon effect on the enhancement and quenching of the luminescence performance of the quantum dots.When the p H value of the system is 8.5,the photoluminescence performance of the quantum dots is optimal.Secondly,using thioglycolic acid（TGA）as the surface modifier,the oil phase quantum dots are extracted and replaced to obtain the water phase TGA-Zn Cd Se S quantum dots.The Zn Cd Se S-Au hybrid is prepared by mixing～20nm Au particles with TGA-Zn Cd Se S quantum dots.The p H value of the coupling system is optimized.The properties of gold nanoparticle concentration and size to obtain the best fluorescence enhancement effect is studied.And then Zn Cd Se S-Au hybrid is used as a light-emitting layer in QLED devices.Finally,by using Ni O and Zn O/Ti O₂ as the hole transport layer and electron transport layer,respectively,an all-inorganic QLED device is constructed.The power efficiency of the corresponding device is 6.2 lm/W,the highest brightness is 1005 cd/m².In comparison with the metal-free QLED,the power efficiency is increased by about 3 times,and the lifetime of the device is also increased.（3）Doping the hole transport layer to improve the luminous efficiency of the device.Based on the research of monochromatic QLED devices,the method of doping the hole transport layer is used to improve the hole transport efficiency in the device,promoting the charge balance and then improving the efficiency of the device.After comparative analysis,it is determined that CBP-doped poly-TPD is used as HTL.And the higher carrier mobility of poly-TPD and the deeper HOMO energy level of CBP are used to improve hole injection efficiency.Compared QLED device with pure poly-TPD as the HTL,the current efficiency of the device based on the doped HTL increase from 3.71 cd/A to 5.41 cd/A,and the power efficiency increase from 2.59lm/W to 4.25 lm/W.At the same time,the method is popularized and applied to red and blue QLED devices.By comparing the performance parameters of three-color devices in organic and inorganic systems,it is found that in the organic system,the efficiency of the three-color devices is slightly higher than that of the inorganic system,but the performance among the three-color devices differs greaty.In the inorganic system,all three-color pixels can be turned on under the almost same current density working conditions,and the light emission uniformity is better,but the brightness value needs to be improved.Therefore,a solution for balanced three-color QLED device display is provided.