The next-generation wearable near-eye displays inevitably require extremely high pixel density due to significant decrease in the viewing distance. For such denser and smaller pixel arrays, the emissive material must exhibit wider colour gamut so that each of the vast pixels maintains the colour accuracy. Electroluminescent quantum dot light-emitting diodes are promising candidates for such application owing to their highly saturated colour gamuts and other excellent optoelectronic properties. However, previously reported quantum dot patterning technologies have limitations in demonstrating full-colour pixel arrays with sub-micron feature size, high fidelity, and high post-patterning device performance. Here, we show thermodynamic-driven immersion transfer-printing, which enables patterning and printing of quantum dot arrays in omni-resolution scale; quantum dot arrays from single-particle resolution to the entire film can be fabricated on diverse surfaces. Red-green-blue quantum dot arrays with unprecedented resolutions up to 368 pixels per degree is demonstrated.

Solution-processed colloidal quantum dots (CQDs) are a promising class of semiconducting materials in view of their tunable optical and electronic properties through the quantum size effect. [1][2][3][4][5] They have been used to fabricate nextgeneration thin-film optoelectronic devices including light-emitting diodes, [6] photodetectors, [7] and solar cells. [8][9][10][11][12][13] For example, recent perovskite quantum dotbased light-emitting devices showed an external quantum efficiency exceeding 20%. [14][15][16][17] Solar cells based on lead chalcogenide CQDs have demonstrated power conversion efficiencies (PCE) of 11.3% [18] and a stabilized output over 150 days when stored in air even without encapsulation, [19] making them candidates for low-cost, stable, and scalable next-generation photovoltaics.While the performance of CQD solar cells has improved rapidly, the fabrication process is still limited to labscale, batch-processing methods, mainly due to reliance on a complex and wasteful multistep layer-by-layer (LbL) ligand exchange method, [20] which to date has been most commonly combined with repeated spin-casting deposition. To overcome this limitation, a solution-phase ligand exchange method was recently developed to realize the single-step fabrication of CQD films. [21][22][23] In particular, inorganic anions such as metal chalcogenide complexes, halides, and metal-free ions (S 2− , OH − , SCN − , etc.) have been successfully applied as capping ligands and improved the colloidal dispersion. However, CQDs capped with anions-CQD inks-are typically dispersed in highboiling-point solvents such as N, N-dimethylformamide (DMF) or N-methylformamide (MFA), which adds complexity to the production of sufficiently thick CQD films. [24] To produce CQD films directly from CQD inks, various approaches have been demonstrated, including centrifugal casting [7] and supersonic spray coating. [25] However, so far, these methods have been limited in scale to batch-processing; large-scale, single-step QD film formation has not yet been realized.One of the main challenges when forming films from CQD inks is to inhibit (or even control) the spatial redistribution of the dispersed solute during late-state evaporation. [26] This redistribution often results in poorly controlled film morphology Solution-processed colloidal quantum dots (CQDs) are attractive materials for the realization of low-cost and efficient optoelectronic devices. Although impressive CQD-solar-cell performance has been achieved, the fabrication of CQD films is still limited to laboratory-scale small areas because of the complicated deposition of CQD inks. Large-area, uniform deposition of lead sulfide (PbS) CQD inks is successfully realized for photovoltaic device applications by engineering the solute redistribution of CQD droplets. It is shown experimentally and theoretically that the solute-redistribution dynamics of CQD droplets are highly dependent on the movement of the contact line and on the evaporation kinetics of the solvent. By lowering the f...

With the recent emergence of flexible and wearable optoelectronic devices, the achievement of sufficient bendability and stretchability of transparent and conducting electrodes (TCEs) has become an important requirement. Although metal-mesh-based structures have been investigated for TCEs because of their excellent performances, the fabrication of mesh or grid structures with a submicron line width is still complex due to the requirements of laborious lithography and pattern transfer steps. Here, we introduce an extremely facile fabrication technique for metal patterns embedded in a flexible substrate based on submicron replication and an area-selective delamination (ASD) pattern. The high-yield, area-specific lift-off process is based on the principle of solvent-assisted delamination of deposited metal thin films and a mechanical triggering effect by soft wiping or ultrasonication. Our fabrication process is very simple, convenient, and cost-effective in that it does not require any lithography/etching steps or sophisticated facilities. Moreover, their outstanding optical and electrical properties (e.g., sheet resistances of 0.43 Ω sq at 94% transmittance), which are markedly superior to those of other flexible TCEs, are demonstrated. Furthermore, there is no significant change of resistance over 1000 repeated bending cycles, with a bending radius of 5 mm, and immersion in various solvents such as salt water and organic solvents. Finally, we demonstrate high-performance transparent heaters and flexible touch panels fabricated using the nanomesh electrode, confirming the long-range electrical conduction and reliability of the electrode.

Achieving high emission efficiency in solidstate quantum dots (QDs) is an essential requirement for high-performance QD optoelectronics. However, most QD films suffer from insufficient excitation and light extraction efficiencies, along with nonradiative energy transfer between closely adjacent QDs. Herein, we suggest a highly effective strategy to enhance the photoluminescence (PL) of QD composite films through an assembly of QDs and poly-(styrene-b-4-vinylpyridine)) (PS-b-P4VP) block copolymer (BCP). A BCP matrix casted under controlled humidity provides multiscale phase-separation features based on (1) submicrometer-scale spinodal decomposition between polymer-rich and water-rich phases and (2) sub-10 nm-scale microphase separation between polymer blocks. The BCP-QD composite containing bicontinuous random pores achieves significant enhancement of both light absorption and extraction efficiencies via effective random light scattering. Moreover, the microphase-separated morphology substantially reduces the Forster resonance energy transfer efficiency from 53% (pure QD film) to 22% (BCP-QD composite), collectively achieving an unprecedented 21-fold enhanced PL over a broad spectral range.

The depletion region width of metal-oxide/quantum-dot (QD) heterojunction solar cells is increased by a new method in which heavily boron-doped n(+)-ZnO is employed. It is effectively increased in the QD layer by 30% compared to the counterpart with conventional n-ZnO, and provides 41% and 37% improvement of J(sc) (16.7 mA cm(-2) to 23.5 mA cm(-2) ) and power conversion efficiency (5.52% to 7.55%), respectively.