Printing Display:Materials Processing And Devices

Display that present information in the form of images have become an important component of the human-computer interactive display interface in the 5G era,therefore,it is very important to adopt cost-effective manufacturing technology to realize the industrialization of display.Low-cost,large-area,high-precision patterning printing technology is an ideal technical solution for preparing display devices,and roll-to-roll printing is also compatible with flexible device fabrication.Materials suitable for printing need to have good solubility.In addition to preparing self-emitting devices such as organic light-emitting diodes(OLED)and quantum dot light-emitting diodes(QLED),inkjet printing can also prepare large-area reflective displays like organic electrochromic devices(EC)as for reflective display.However,the films prepared by inkjet printing technology still have problems such as the“coffee ring”effect,the different drying morphologies of the droplets at different positions,and the low resolution of the printed patterns.These problems will affect the uniformity of film within the pixel even the entire panel,and the resolution of the display,and ultimately result discounts on device performance and display quality.In view of the above problems,this paper starts research from the perspective of inkjet printing film and devices,with the purpose of further promoting the application and development of printing display.This paper first systematically studied the inkjet printing film regulation based on the new soluble small molecule host material t-BuCz-m-NPBI designed and synthesized in our laboratory.The film printed with small molecule ink is prone to coffee ring and dewetting problems.By adopting the single-solvent o-dichlorobenzene solvent system,uniform light-emitting film is obtained.The maximum current efficiency of the printed small molecule red OLED device is 17.89 cd/A.Based on the single-solvent system,by controlling the capillary outflow and the pinning of the contact line,the coffee ring and dewetting in inkjet printing organic small molecule film is solved,and a film with uniform thickness is obtained.The maximum current efficiency of the small molecule red OLED device with the printed red phosphorescent layer t-BuCz-m-NPBI:9 wt%Ir(MDQ)₂(acac)is 17.89 cd/A.Secondly,the printing of Zn O NPs(Zinc oxide nano particles),the key electron transport material in Quantum dot light emitting diodes(QLED),is studied.The addition of ethanolamine ligand in the Zn O synthesis process improves the uniformity of nanoparticle dispersion,and the adjustment of the ligand content during the ink preparation process prevents the agglomeration of nanoparticles caused by the lack of ligand,all of those methods can improve the uniformity of inkjet printing Zn O film.The current efficiency of the QLED printed with Zn O NPs modified by diethanolamine(LE is 11.9 cd/A)is improved to about 88%of that of spin-coated one(LE is13.5 cd/A).Based on this,120 PPI(Pixel per inch)bottom-emitting Active Matrix full-color QLED and 240 PPI top-emitting full-color QLED printed displays were fabricated.Under 5 V driving voltage,the emission of red,green,and blue layer is perfect without cross-talk image.And the brightness of the printed flexible QLED device is not significantly attenuated after10,000 bending circles.In order to improve the resolution of printing display,the electrohydrodynamic printing is adopted to pattern ultra-fine film.After optimizing a variety of solvents,using cyclohexanone,a polar solvent with a higher dielectric constant,as the solvent,and a nozzle with a diameter of1.5?m,the line widths of high-quality red,green,and blue polymers are reduced to 1.5?m and1.7?m and 1.6?m respectively.A green passive matrix display device with a resolution of2115 PPI is fabricated.In additon to prepare a full-color reflective EC display,a full-color scheme is designed and its printing film morphology is explored.The“color additive”pixel plane layout is firstly adopted as a reflective electrochromic device that using intrinsically“color subtractive”to achieve full color.Based on color gamutthe of EC device obtained through theoretical simulation calculation(theoretical contrast ratio of the display device reaches 16:1,and the color gamut is about 10.5%),it is proposed to use Color Map to match colors,for it is difficult for EC polymer to achieve grayscale while keeping the color unchanged.According to the above color reproduce scheme,the pixel arrangement is determined to be red,green,and blue in sequence.So far,the monochrome EC display prototype can display images well,and the conjugated EC red polymer ink formulated with a single solvent has stable printing atbility and uniform film morphology.