Fig. 1. Structure, size effect, and development status of quantum dots (QDs). (a) Core-shell structure diagram of QD^[8]; (b) relationship between QD size and emission bandgap^[12]; (c) color gamut representation of RGB quantum dot light emitting diodes (QLEDs)^[13]; (d) development trend of external quantum efficiencies (EQEs) in QLEDs^[14]

Fig. 2. Research on patterning of QDs using inkjet printing. (a) Schematic of inkjet printing^[15]; (b) fluorescence microscope image of patterns printed on glass by super-inkjet printing system, and minimum linewidth is 1.65 μm^[23]; (c) magnified electroluminescence images of red and green sub-pixels when lightening simultaneously^[30]; (d) current efficiency curves of bottom and top emission patterned QLEDs^[30]; (e) light-on photograph of inkjet-printed QLED with bias voltage of 4 V^[33]; (f) electroluminescence (EL) microscope image of subpixel with inkjet-printed QD film using QD inks containing 90% cyclohexylbenzene with volume ratios^[33]; (g) atomic force microscope (AFM) image of inkjet-printed QD film^[33]; (h) current efficiency-current density curve of inkjet-printed QLEDs^[33]; (i) current density-voltage-luminance (J-V-L) curve of inkjet-printed red QLEDs^[33]

Fig. 3. Flow chart of full-color QLED fabrication based on traditional photolithography^[34]

Fig. 4. Flow chart of full-color passive-matrix QLED fabricated via sacrificial layer assisted photolithography^[35]

Fig. 5. Research on preparation of QD patterns using direct photolithography method. (a) Illustration of photolithography process for patterning of QDs^[37]; (b) schematic of QD surface combined with PEI under ultraviolet light^[37]; (c) structure schematic of full- color QLEDs^[37]; (d) J-V-L graph of patterned QLEDs^[37]; (e) current efficiency of patterned QLEDs^[37]

Fig. 6. Method of forming QD patterning using light-driven ligand crosslinking agents. (a) Schematic description of ligand crosslinking process between neighbouring QDs based on C-H insertion reaction of nitrene moiety of LiXer^[39]; (b) schematic description of optical patterning process of QDs using LiXer, patterns of horizontally aligned red, green, and blue QDs, and vertically stacked patterns of RGB QDs obtained by continuously applying optical patterning process^[39]; (c) fluorescencemicroscopic image of RGB QD patterns that are obtained through consecutive photo-patterning processes^[39]; (d) magnified view of (c)^[39]

Fig. 7. Research on direct photolithography patterning of QDs. (a) Schematic illustrations of patterning of direct optical lithography of QD^[40]; (b) process of using photo-patternable emissive nanocrystal inks for patterning luminescent QDs^[40]; (c) fluorescence microscopic image of green QD pattern with a minimum line width of 1.5 μm^[40]

Fig. 8. Research on preparation of QD patterns by electrophoretic deposition. (a) Zeta potentials of QDs capped with different ligand contents^[42]; (b) schematic illustration of process for preparing patterned QDs by electrophoretic deposition^[42]; (c) fluorescence microscope image of green QD pattern with a resolution of 1093 ppi^[42]; (d) fluorescence images of RGB QD patterns fabricated by three-step electrophoretic deposition. Scale bar is 200 μm; (e) magnified view of (d). Scale bar is 50 μm^[42]

Fig. 9. Research on inducing QDs to deposit in selected areas using asymmetric wettability. (a) Diagram of a single liquid bridge with an asymmetric contact angle between template and substrate^[43]; (b) moving direction of small-size QD nanoparticles during solution dewetting processes in a single capillary trail confined between template and substrate in rectangle space^[43]; (c)-(f) schematic illustration of asymmetric wettability template technique for assembling patterned QD microarrays. A continuous liquid of QD solution is immersing into groove between silicon templates, and substrate is dewetting into individual liquid bridges owing to guidance of template structure, yielding patterned QD microarrays after solution is total evaporated^[43]

Fig. 10. Research on QD patterning using optical microcavities. (a) Schematic illustration of RGB QLED array ^[50]; (b) pixelated QD arrays with square pixel shape from 10 to 5 µm and line pixel shape from 3 to 1 µm^[50]; (c) J-V-L curve of converted emission^[50]; (d) color coordinate diagram of RGB QD luminescence achieved through optical microcavity color conversion^[50]

Fig. 11. Research on preparation of QD patterns using transfer printing. (a) Schematic illustration of intaglio transfer printing process^[51]; (b) schematic of immersion transfer-printing process^[52]; (c) schematic illustration of a process for sacrificial layer assistant multilayer transfer printing^[53]; (d) schematic of Langmuir-Blodgett-transfer printing process and fluorescence microscopy images of of patterned red and green QD films^[54]

Fig. 12. Research on in-situ preparation of perovskite QD patterns. (a) Schematic diagram of in-situ inkjet printing strategy for fabricating patterning perovskite QD patterns on polymer substrate^[55]; (b) RGB perovskite QD patterns under UV light illuminations^[55]; (c) photography of large-area patterned perovskite QD layers^[56]; (d) flow chart of in-situ preparation of perovskite QDs by laser writing^[57]

Fig. 13. Summary of main factors affecting lifetime performance of QLEDs^[58]