| Quantum dot Light-Emitting Diode(QLED)has the advantages of high color purity,wide color gamut and long lifetime,and has a great development prospect in the field of lighting and display.With the improvement of quantum dot synthesis process and optimization of device structure,QLED performance has made a major breakthrough,and the relevant performance can initially meet the requirements of commercial applications,but the construction of QLED devices with high efficiency in large areas is still a challenge,which hinders the commercialization process.At present,the commonly used methods for preparing QLED films include spin coating,Langmuir-Blodgett technology and inkjet printing,which still have problems such as waste of raw materials,complicated process and low preparation efficiency.The group has recently developed a liquid-bridge printing technique for efficient printing of quantum dot film.It is shown that the de-impregnation process is an important factor affecting the film quality of liquid-bridge printing,so it is an important idea to further improve the quality of quantum dot film by changing the solvent de-impregnation process.In order to regulate the rewetting process of liquid bridge printing film formation,increase the modulating effect of solvent volatilization process on the deposition behavior of quantum dot nanoparticles,and further improve the film structure modulation ability,this thesis introduces a binary solvent system in the liquid bridge printing process,changes the surface tension,boiling point and other related factors of the solvent,and regulates the quantum dot film formation process by enhancing the inward Marangoni flow,improves the quality of quantum dot film,and thus enhance the performance of QLED devices.The surface tension and boiling point of binary solvents were studied to reveal the mechanism of binary solvents to improve the quality of QLED films.The results show that the surface tension gradient formed by the binary solvent system effectively enhances the controllability in the deposition process of quantum dot film prepared by the liquid-bridge method,which provides a new method to realize the construction of high-performance QLED devices.The main research contents of this paper are as follows:(1)To explore the regulatory effect of binary solvent on the deposition behavior of quantum dot:Using n-octane(22.6 dyne/cm,125.6℃)as the main solvent,N-tridecane(26.0 dyne/cm,234℃),chloroform(28.9dyne/cm,61.3℃),cyclohexane(32.8 dyne/cm,238.5℃)and o-dichlorobenzene(36.7 dyne/cm,180.4℃)and other solvent with different surface tension and boiling point can regulate the deposition process of quantum dot,which are mixed with n-octane respectively to form four different binary solvent systems.By accurately regulating the binary solvent system,the ratio between solvent,the printing speed and the concentration of the quantum dot solution,the deposition process of the quantum dot film was optimized.Finally,the preparation of high-quality quantum dot film was realized when n-octane:cyclohexane=7:3,the printing speed was 7 mm/s,and the concentration of the quantum dot solution was 18 mg/m L.(2)Based on the controllable preparation of quantum dot film,QLED device were constructed by liquid bridge printing in the atmospheric environment,and the electroluminescence performance of quantum dot film for QLED device under different printing conditions was compared.The effects of film annealing temperature and annealing time on device performance were discussed.By optimizing the device process,the optimal annealing temperature was determined to be 60℃and the optimal annealing time was 5 min,among which the maximum external quantum efficiency of the green QLED device was 17.92%,the maximum brightness was 238400 cd/m~2,and the maximum current efficiency was 77.03 cd/A.The preparation of 1.5 cm×1.5 cm green large-area by liquid bridge printing technology is realized,which provides a new method for the efficient and low-cost preparation of high-performance QLED. |
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