Fig. 1. (a) Core-shell structure diagram of the colloidal quantum dot^[20]; (b) Structure diagram of perovskite nanocrystal^[21]; (c) Relationship between quantum dot size and emission bandgap^[22]; (d) Excitation mechanisms of quantum dots^[16]; (e) Color gamut representation of RGB QLEDs^[17]

Fig. 2. (a) The schematic diagram of the aerosol jet printing; (b) Full color quantum dots based Micro-LED image under fluorescence microscopy^[30]; (c) The process of the full-color emission quantum dots based Micro-LED by aerosol jet printing^[31]

Fig. 3. (a) Schematic illustration of the marangoni flow and capillary flow: surface tension at the top area of the droplet is smaller than the edge(Δγ<0), and surface tension at the top of the droplet is larger than the edge area(Δγ>0); (b) Fluorescence image and corresponding surface profiles of the microarray with dodecane volume ratio of 60%, 70%, and 80% in the ink. The scale bars are 100 μm; (c) A CsPbBr₃ quantum dot pattern by inkjet printing^[33]

Fig. 4. (a) Fluorescence microscope image of patterns printed on the glass by super-inkjet printing system, the minimum linewidth is 1.65 μm^[34]; (b) Red quantum dot pattern by electrohydrodynamic printing with a diameter of 1 μm^[35]

Fig. 5. (a) Illustration of the quantum dot patterning by using repeated photolithography; (b) Microscope image of the patterned quantum dot under 405 nm laser excitation; (c) Large-scale quantum dot pattern demonstration on a 4 inch quartz wafer under UV lamp^[36]

Fig. 6. (a) Schematic illustrations of the patterning concept of direct optical lithography of quantum dot; (b) Process of using photo-patternable emissive nanocrystal inks for patterning luminescent quantum dots; (c) Fluorescence optical microscopy images of green quantum dots pattern with a minimum line width of 1.5 μm^[41]

Fig. 7. (a) Zeta potentials of quantum dots capped with different ligand contents; (b) Schematic illustration of the quantum dots patterning process on the prefabricated substrate; (c) Fluorescence image of the red quantum dot stripe array with a line width of 2 μm. Scale bar: 10 μm; (d) Fluorescence images of RGB quantum dot patterns fabricated by three steps selective electrophoretic deposition. Scale bar: 200 μm(left) and 50 μm(right)^[43]

Fig. 8. (a) Schematic diagram of a single pixel of the full color Micro-LED display based on red and green quantum dots; (b) Process of red and green quantum dots injection in the micro-channels; (c) SU-8 mold on the silicon substrate; (d) PDMS microchannel bond with the glass substrate with a sub pixel of 50 μm×140 μm; (e) Quantum dot color conversion layer with 200 μm full-color pixel pitches array^[44]

Fig. 9. (a) Schematic diagram of in situ inkjet printing strategy for fabricating patterning perovskite quantum dots patterns on polymer substrate; (b) Printed RGB perovskite quantum dots patterns under UV light illuminations^[49]; (c) Photography of patterned perovskite-polymer composite sheets^[51]; (d) In situ direct laser writing fabrication of perovskite quantum dots patterns inside of the glass^[52]; (e) In situ direct laser writing fabrication of perovskite quantum dots with different colors inside of the glass^[53]

Fig. 10. Representative mechanisms for the instability of QDs, including photoactivation, photocorrosion, and thermal degradation^[54]

Fig. 11. (a) Structure design of the QLED devices; (b) Energy level diagram of the QLED; (c) Schematic of electrohydrodynamic printing to fill the pixel on the substrate^[35]; (d) The fluorescent microphotograph of high-resolution pixels by electrohydrodynamic printing; (e) The scheme of droplet evaporation processes for heat post-treatment (HP) and gradient vacuum post-treatment (GVP) methods. EQE-luminance curves of (f) red, (g) green, and (h) blue inkjet printing(circle) and spin-coating(square) QLED. The scale bar is 5 cm in the insert picture^[49]

Fig. 12. (a) Schematic illustration of patterning QDs with different color on a substrate via scarify layer assisted photolithography approach; (b) The device structure of Micro-QLED; (c) The electroluminescent image of the 500 ppi full-color Micro-QLED array^[37]; (d) Schematic description of the ligand crosslinking process between neighboring quantum dots based on the C-H insertion reaction of the nitrene moiety of LiXer; (e) Schematic description of the photo-patterning processes of quantum dots using LiXer; (f) External quantum efficiency (EQE) – current density characteristics of pristine and cross-linked QLED devices; (g) Lifetime measurement of pristine and cross-linked QLED devices with an initial luminance of 11000 cd/m². The sub pixel size in the inset image is 10 μm×38 μm^[42]

Fig. 13. Optoelectronics properties of QLED by selective electrophoretic deposition.(a) Schematic diagram of the device structure of SEPD processed QLEDs; (b) Energy band diagram of the QLEDs; (c) Image of red and green SEPD QLED pixels. Scale bar: 5 mm and 0.1 mm; (d) Normalized electroluminescent spectra of red and green SEPD QLEDs; (e) Current density - luminance - voltage (J-L-V) characteristics of the red and green SEPD QLEDs; (f) Current efficiency - current density of SEPD QLED (solid line)^[43]

Fig. 14. Micro-QLED by transfer printing.(a) Schematic of transfer printing process for patterning of quantum dots; (b) Electroluminescence image of a 4-inch full-color quantum dot display with a resolution of 320×240^[60]; Confocal fluorescence images of full-color RGB quantum dots arrays with subpixel width of (c) 3 μm and (d) 0.5 μm; (e) Current density–voltage–luminance (J–V–L) characteristics of immersion transfer printing (yellow line) and contact printing (green line) devices^[61]; (f) Schematic of the langmuir-Blodgett method assisted transfer printing process; (g) Fluorescence microscopy image of patterned red-QD-film arrays with scale bar of 5 μm and 3 μm (insert picture); (h) Schematic of the patterned red micro-QLED^[62]

Fig. 15. Realization of full color Micro-QLED by optical resonant cavity^[66]. (a) Schematic device structure of QLED; (b) Working principle of RGB micro-cavity based QLED; (c) The color coordinates and color triangle of the converted red, green, and blue emission. The color gamut can achieve 110% NTSC; (d) Pixelated QLED arrays with square pixel shape and subpixel size from 10 µm to 5 µm, and line shape with subpixel size from 3 µm to 1 µm

Fig. 16. Degradation mechanism in QLEDs, including material instability, charge imbalance and exciton decay^[54]