Anionic structural effect in liquid–liquid separation of phenol from model oil by choline carboxylate ionic liquids

Anionic structural effect in liquid–liquid separation of phenol from model oil by choline carboxylate ionic liquids

Research Article Cite This: ACS Appl. Mater. Interfaces 2019, 11, 28520−28526 www.acsami.org Asymmetric Wettability Interfaces Induced a Large-Area ...

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Research Article Cite This: ACS Appl. Mater. Interfaces 2019, 11, 28520−28526

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Asymmetric Wettability Interfaces Induced a Large-Area Quantum Dot Microstructure toward High-Resolution Quantum Dot LightEmitting Diodes Xiaoxun Li,† Binbin Hu,*,† Zuliang Du,† Yuchen Wu,*,‡ and Lei Jiang‡

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Key Laboratory for Special Functional Materials of Ministry of Education, National & Local Joint Engineering Research Centre for High-Efficiency Display and Lighting Technology, School of Materials and Engineering, Collaborative Innovation Centre of Nano Functional Materials and Applications, Henan University, Kaifeng 475004, P. R. China ‡ Key Laboratory of Bio-Inspired Materials and Interfacial Science, Technical Institute of Physics and Chemistry, Chinese Academy of Sciences, Beijing 100190, P. R. China S Supporting Information *

ABSTRACT: Precisely patterning large-area quantum dot (QD) nanoparticles is an essential technique for enhancing high-resolution and high-performance in the next-generation display QLEDs. However, conventional solution-based assembly techniques suffer from trade-offs between large-scale and spatial precision. As such, large nondefect areas and ordered stacking of QD assembly architectures are difficult to achieve, and both are essential to fabricating a highperformance device. Herein, we demonstrate a facile method for assembling the QD nanoparticles into a microstructure using an asymmetric wettability template to regulate the dewetting process. The wettability difference of the interface induces the continuous liquid film to recede into individual liquid bridges, which enabled unidirectional dewetting and regulated the QD solution mass transport. In addition, because of the asymmetric wettability between the substrate and template, large-scale, ultrafine (1 μm), and highly flat microwire QD arrays with the precise position and strict alignment are easily assembled and transferred onto the target substrate. The method has been further introduced into the fabrication of high-resolution patterned QLED devices, with maximum electroluminescence values of 73 490, 4357, and 950 cd/m2 for green, red, and blue, respectively. This research provides a novel and facile perspective for manufacturing highresolution and high-performance patterned QLED devices. KEYWORDS: quantum dots, asymmetric wettability, assembly, micro-structure, QLEDs



INTRODUCTION Colloidal quantum dots (QDs) have been intensely investigated because of their highly advantageous characteristics, including low-cost solution-processing, narrow emission spectra, tunable emission wavelength, and high luminescent efficiency;1−7 all of which make them the most popular materials in QD light-emitting diode (QLED) technology.8−11 Of particular interest is using a patterned QD microstructure as the light-emitting layer in QLEDs for the purpose of implementing them into new candidates for the nextgeneration display.12−15 Recently, various approaches have emerged to utilize solution-based fabrication processes in order to deposit patterned QD microstructures in QLED devices, such as inkjet printing,16−21 transfer printing,22−26 and mask printing,27−29 among others.30−32 However, all these techniques suffer from trade-offs between high-cost, complex processing, large-scale, and spatial precision. Thus, developing a facile, feasible, and innovative technique to jointly mitigate all the issues associated with assembling a QD microstructure in QLED devices remains a significant challenge. Generally, miniaturized liquid droplets or thin films are located with predetermined patterns for regulating the spatial © 2019 American Chemical Society

position, dewetting, and evaporation of liquid necessary to assemble a QD microstructure. However, owing to solution’s random and uncontrollable dewetting dynamics, the longrange-ordered QD nanoparticles are difficult to precisely assemble. The gas−liquid−solid three-phase contact line (TCL), which are pinned or unpinned,33,34 (called coffeering effect) on the substrate will disorder the assembly blocks in the dewetting process.35,36 Thus, large nondefect areas and ordered stacking of QD assembly architectures are difficult to achieve. Therefore, to obtain a precisely patterned QD microstructure, a directional force is required to induce the QD solution fluidic flow and mass transport. Recently, Jiang et al.,37−42 have designed a highly efficient method to manipulate the dewetting dynamics of various solutions, yielding longrange-ordered 1D assembly microstructures. However, the ultrasmall size of QD nanoparticles (ca. 10 nm), combined with the fact that they are easily influenced by the coffee-ring effect during solution-processed deposition, makes it difficult Received: May 21, 2019 Accepted: July 15, 2019 Published: July 15, 2019 28520

DOI: 10.1021/acsami.9b08603 ACS Appl. Mater. Interfaces 2019, 11, 28520−28526

Research Article

ACS Applied Materials & Interfaces

Figure 1. Schematic of assembling patterned QD microarrays: (a) The cartoon diagram of a single liquid bridge with an asymmetric CA between template θ1 and substrate θ2. The CA of the silicon template and target substrate with an oil CA of 45° ± 1° and 2° ± 0.5°, respectively. (b) The moving direction of small-size QD nanoparticles during the solution dewetting processes in a single capillary trail confined between the template and substrate in the rectangle space. (c−f) Schematic illustration of the asymmetric wettability template technique for assembling patterned QD microarrays. A continuous liquid of QD solution is immersing into the groove between the silicon template, and the substrate is dewetting into individual liquid bridges owing to the guidance of the template structure, yielding the patterned QD microarrays after the solution was total evaporated. (g−j) In situ fluorescent microscopy observation of the liquid dewetting processes and the formation of the divisive liquid bridges in the sandwich system corresponding to the schematic photograph in (c−f).

to induce the fluidic flow and enable mass transport for precise assembling. Therefore, fabricating patterned QD microstructure arrays with large areas, high density, and strict alignment remains a significant challenge. Herein, we demonstrate a simple and effective method for assembling QD microstructure arrays by using an asymmetric wettability template to regulate the dewetting process. In this approach, the line-shaped micropillar structure on the template plays an important role in generating an asymmetric wettability interface, which manipulates the QD solution unidirectional dewetting. As the solution recedes in the assembly system, the wettability difference of the interface induces the continuous liquid film to recede into individual liquid bridges and become pinned on the top of the micropillar, which enables unidirectional dewetting and regulates the QD solution mass transport. Because of Laplace pressure,40,43 the directional receding of the QD solution drives the moving nanoparticles from the gaps to the micropillar tops. Subsequently, a QD microstructure with the precise position, good homogeneity, and ultrasmooth texture is assembled and transferred onto a select area, accompanied by a controllable TCL-receding process of the individual liquid bridge. Two essential elements have the asymmetric wettability in this sandwich system to manipulate the liquid dewetting dynamics and yield a large nondefect area and long-range-ordered QD microstructure on the target substrate. One is the asymmetric wettability between the silicon grooves and the micropillars, which ensures the formation of individual liquid bridges. The other is the difference in wettability between the flat substrate and microstructure template, which attains a facile transfer of the assembled microstructure QD arrays without any residual. Here, we assembled large-scale (300 × 250 μm2), ultrafine (1 μm), and highly flat microwire QD arrays with the precise position and strict alignment. Of particular note, the wellassembled QD microstructure arrays are successfully implemented into the QLED device as the high-resolution lightemitting layer. Furthermore, we fabricated the high-resolution and high-performance patterned QLED devices with maximum

electroluminescence (EL) values of 73 490, 4357, and 950 cd/ m2 for green, red, and blue, respectively. It is expected that this technique will present a new alternative to enhance highresolution and high-performance of QLED display.



RESULTS AND DISCUSSION

In order to assemble patterned QD microstructure arrays, a typical width 2 μm, gap 5 μm, and height 10μm, micropillar template was prepared. An optical image of the top view is shown in Figure S1 (Supporting Information). UV microreplication against a nickel master structure was employed to manufacture the structured template; via deep reactive ion etching (DRIE, details in the Experimental Methods). Next, the substrate was modified with a monolayer of FAS by means of vapor deposition (see the Experimental Methods). Thus, because of the interaction between the FAS and the microstructure, the template became superhydrophobic, and the water contact angle (CA) increased from 110° ± 2.1° to 150° ± 2.7° (Figure S2). Therefore, the asymmetric wettability interface was formed and then used for manipulating the unidirectional solution dewetting. Figure 1 schematically depicts the solution dewetting mechanisms and regulating process on the asymmetric wettability interface to yield the long-range-ordered assembly. In this sandwich system, there are two essential parts of the asymmetric wettability interface that enables QD nanoparticles to assemble on the target substrate. (1) Between the groove and pillar, when the silicon template was modified by FAS, the wettability difference increased between template’s groove and pillar (Figure S2), which ensures the formation of individual liquid bridges. (2) Between the flat substrate and microstructure template, as shown in Figure 1a, the oil (octane) CA on the template is 45° ± 1° and on the substrate is 2° ± 0.5°, which achieves a facile transfer of the assembled microstructure QD arrays onto the substrate without any residual. Figure 1c−f is a cartoon schematic that demonstrates in detail this method’s assembly process. At first, a continuous liquid film is immersed into the grooves between the silicon micropillar 28521

DOI: 10.1021/acsami.9b08603 ACS Appl. Mater. Interfaces 2019, 11, 28520−28526

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ACS Applied Materials & Interfaces

Figure 2. (a) Transmission electron microscopy (TEM) image of green QD nanoparticles. (b) PL image of patterned QD microarrays under 375 nm laser as an excitation source. (c) Optical image of patterned QD microarrays corresponding to the PL image. (d) Scanning electron microscopy (SEM) image of QD microarrays with the precise position and strict alignment. (e) Zoom-in SEM image of a single assembled microwire. (f) AFM image of a single-assembled QD microwire. (g) Single QD microwire’s smooth surface and straight boundary and its width and height.

was divided into individual liquid bridges anchored on the top of the micropillars, and no QD nanoparticles were left in the gaps, as confirmed by the absence of fluorescence (Figure 1i). After the solvent of each pinned liquid bridge was totally evaporated, the QDs were assembled into the microstructure arrays with the precise position and strict alignment on the select area (Figure 1j). Finally, due to the asymmetric wettability between the substrate and template (Figure 1a), the individual liquid bridge had an inverted trapezoidal section profile with a different CA θ1 and θ2, θ1 > θ2, causing the liquid to easily adhere to the substrate. As such, the patterned QD arrays could be easily transferred onto the desired substrate. Therefore, this technique offers a novel and facile approach for assembling QDs into long-range 1D microstructures. Temperature and solution concentration are the two essential variables, so serial experiments were designed and conducted to identify optimal condition for both. Figure S5 shows that when the temperature was <140 °C, all the transferred QD microarrays were positioned with the precise position and strict alignment. In contrast, when the temperature is >140 °C, which is 15 °C higher than the solvent boiling point, the assembled microwires became disordered and chaotic. Obviously, a higher temperature accelerates the dewetting speed and shortens the fabricating time. After correlating the relationship between the assembly speed and the ambient temperature, it was determined that the assembly time can be shortened to within 5 min, if the temperature is >100 °C (Figure S6). However, a temperature >100 °C will lead to irreversible damage of the QLEDs and other functional layers. With respect to solution concentration, when <8 mg/ mL, the bubble area on the covered substrate emerged because of inadequate solution evaporation (Figure S7). When >8 mg/ mL, the assembled QD microarrays were positioned with the precise position and strict alignment. Interestingly, using our method, the width of each single microstructure increased from 1 to 3 μm as the concentration increased from 8 to 15 mg/mL. As such, high-quality QD microstructure could be achieved by adjusting solution concentration and ambient temperature. Using this strategy, we prepared the large-area and longrange-ordered QD microstructure array with the precise position and strict alignment observed in Figure 2. Figure 2a is a transmission electron microscopy (TEM) image that

template and the substrate (Figure 1c). With the development of solvent evaporation and solution dewetting, continuous liquid film dewetted to one edge of the template, leaving liquid bridges on the tops and liquid tails in the gaps (Figure 1d). After dewetting of all continuous liquid films, individual liquid bridges were anchored on the top of the micropillars (Figure 1e). Consequently, QD nanoparticles were assembled onto the target substrate with regulated positions after the solvents totally evaporated (Figure 1f). Note that the cartoon detailing the assembling process mechanism in the top-pinned liquid bridges is shown in Figure S3. To gain further insight into the mechanism of this approach, in situ fluorescent microscopy, with an excitation source under 375 nm, was used to observe the evaporation and dewetting process of the QD solution immersed in the sandwich system (Figure 1g−j). At first, the QD solution was fully filled into the microgrooves and confined between the bottom micropillars and top substrate (Figure 1g). With evaporation of the solvent, the QD solution filled in the silicon gap where unidirectional dewetting was evaporation-driven to the edge of the template at the first stage (see Figure S4). Using an optical microscope, we observed the QD solution-receding process while confined in the sandwich system. Every 60 s, the receding process in the silicon groove was imaged. The red line indicates a single groove receding the process direction, which is toward the template edge. Yet, the residual QD solution was pinning onto the top of the micropillars and left the individual liquid bridges anchored on the micropillar tops and the crescent liquid trails in gaps’ rectangular spacing (Figure 1h). Thus, there is a unidirectional shearing force inside the liquid trails, which forces the movement of QD nanoparticles into the pinning liquid bridges (Figure 1b). There are two primary reasons for these asymmetric dewetting and nanoparticle moving behavior to be triggered in this sandwich system: (1) difference of the equivalent capillary size40 and (2) the asymmetric wettability interface.37,38 When solution is confined in the sandwich system, due to the equivalent capillary size difference between the template tops and grooves, higher Laplace pressure emerges at the top of the micropillars, giving rise to this directional dewetting and nanoparticle movement behavior. Similarly, the asymmetric wettability interface between the microgrooves and the micropillars induces the formation of the individual liquid bridge. Therefore, a continuous liquid film 28522

DOI: 10.1021/acsami.9b08603 ACS Appl. Mater. Interfaces 2019, 11, 28520−28526

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Figure 3. Schematic depicting fabrication of patterned QLED devices via asymmetric wettability template technique. (a) A functional ITO substrate with PEDOT:PSS and TFB layers covered onto the silicon template to force the immersed and confined solution into the sandwich system. (b) After the total solution has evaporated, the assembled QD microarrays are transferred onto the functional ITO substrate surface. (c) The other functional layers are successively fabricated on the ITO to make an integrated patterned QLED device. (d) Schematic diagram of the ITO/PEDOT:PSS/TFB/patterned QDs/ZnO/Al QLED devices. (e) Energy diagram of our multilayer structured QLED devices.

Figure 4. (a−c) Fluorescence image of patterned QD microarrays of red, green, and blue under 375 nm laser as an excitation source. (d−f) EL photographs of patterned red, green, and blue QLEDs, operating at 4 V. (g) CIE coordinates of three-color QLEDs at their corresponding EL maxima. (h) J−L−V characteristics of patterned red, green, and blue QLEDs.

ing atomic force microscopy (AFM) image and topography diagram (Figure 2f,g) further demonstrate the trapezoidal QD microstructure assembly, of which the height is 150 nm, and the top and bottom width of a typical micro-structure are ∼1 and 1.5 μm, respectively. These widths are smaller than that of the 2 μm wide micropillars because of the dewetting and shrinking of the liquid bridges pinned on the top of the micropillars. In addition, low surface energy of the FASmodified micropillars template is an important property for stably assembling good homogeneity and distinct QD microstructure boundaries. Without FAS modification, there would be a highly rough surface and disordered boundaries in the QD microstructure (Figure S10). Furthermore, by changing silicon template’s microstructure, various shapes of the patterned QD assemble block, such as point, triangle, quadrangle, square, pentagon, and hexagon, were achieved (Figure S11).

depicts green, homogeneous, mono-dispersed CdSe/ZnS QD nanoparticles with a diameter of 11 nm. TEM images for two other QD nanoparticle colors and their absorption and normalized fluorescence spectrum are also present in Figure S8. Figure 2b,c shows the photoluminescence (PL) image of large-area and long-range-ordered green QD assembly arrays under a 375 nm laser as an excitation source and its corresponding optical image. Note that at high resolution, the patterned QD arrays exhibit good uniformity, with a 1 μm width, 5 μm interval, and no residual gaps. The scanning electron microscopy (SEM) image of the patterned QD microwire arrays with an ultrasmooth surface and distinct boundary is illustrated in Figure 2d. PL and SEM images of the large-area (300 × 250 μm2) QD microwire arrays are also shown in Figure S9. Furthermore, the zoom-in SEM image (Figure 2e) also depicts the smooth surface and singleassembled QD microwire straight boundary. The correspond28523

DOI: 10.1021/acsami.9b08603 ACS Appl. Mater. Interfaces 2019, 11, 28520−28526

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ACS Applied Materials & Interfaces

ordered microarrays. In this method, the interface wettability difference induced the continuous liquid film to recede into individual liquid bridges, which enabled unidirectional dewetting and regulated mass transport of the QD solution. Thus, three-colors, high-flatness, and high-resolution patterned QD microarrays with a 1 μm width and a 5 μm interval were assembled on the target substrate. We implemented the patterned QD microarrays into the QLED lighting device, which resulted in high-resolution, high-performance QLED devices with maximum luminance values of 4357, 73490, and 950 cd/m2 for red, green, and blue QLEDs, respectively. Therefore, we demonstrated a novel technique for developing high-resolution patterned QLED devices.

In this work, an established method of assembling QD microarrays has been extended to fabricate a high-resolution patterned QLED device (Figure 3). QLEDs are composed of multiple layers, all of which are functional layers that contribute to making it an excellent lighting device. Essentially, indium tin oxide (ITO), poly(ethylenedioxythiophene):polystyrene sulphonate (PEDOT:PSS), a poly(9,9-dioctylfluorene-co-N-(4-(3methylpropyl))diphenylamine) (TFB), QD layer, and ZnO layer are on the top of the Al electrodes (Figure 3d). An energy level diagram of each layer is depicted in Figure 3e and theoretically confirms the practicality of this multilayer device. In this device, TFB is a hole-transport layer (HTL) and ZnO is an electron-transport layer (ETL), and the QD layer had been assembled between HTL and ETL. The cartoon in Figure 3a− c, schematically demonstrates the process of fabricating integrated patterned QLEDs. The detailed preparation process requires a special substrate (ITO glass) to be successively spincoated with PEDOT:PSS and TFB layers and then used to cover an asymmetric wettability template to form a sandwich system (Figure 3a). The system was then held at 80 °C ambient temperature for 30 min. Thus, the patterned QD microwire arrays were assembled and transferred onto the target substrate (Figure 3b). As a consequence, we integrated a patterned light-emitting layer into the QLEDs after spincoating a ZnO layer and evaporating the Al electrode (Figure 3c). Therefore, the QLED device with a high-resolution patterned QD layer was simply and effectively generated using the method described. Figure 4 demonstrates the different color-patterned QLED devices for red, green, and blue, respectively; and the performance of these patterned devices were also evaluated. Figure 4a−c shows the PL image of the different colorpatterned QD microarrays with a 1 μm width and 5 μm interval. Figure 4d−f shows the EL photographs of the patterned QLEDs operating at 4 V. Each of the QLED devices exhibits a high-resolution property due to using the patterned QD microarrays as the light-emitting layer. For the red, green, and blue, respectively, the maximum luminance of these devices is 4357, 73490, and 950 cd/m2 (Figure 4h); maximum external quantum efficiency (EQE) is 0.8, 1, and 0.08%; and the normalized EL spectrum is 634, 530, and 434 nm (Figure S12). Clearly, the QLED devices with a patterned lightemitting layer have much lower luminance and higher current density than the QLED device with a membrane layer because of the smaller luminance area and current leakage (Figure S12). However, these issues can be resolved by using full-color patterned QD microarrays with interval red, green, and blue assembled QD nanoparticles to fill up the active layer. This system can then be integrated into full-color QLED devices for the next-generation display. Finally, Figure 4g displays the CIE coordinates of three-color QLEDs at their corresponding EL maxima: the red are in (0.5689, 0.2698), green are in (0.1698, 0.7402), and blue are in (0.1635, 0.1437). The wide color extent further indicates that these patterned QLEDs put forward a novel alternative for fabricating high-resolution and high-performance QLED displays.



EXPERIMENTAL METHODS

Fabrication of Micropillar-Structured Templates. Silicon wafers (10 cm diameter, N doped, ⟨100⟩ oriented, 400 μm thick) were structured using a direct laser writing apparatus (Heidelberg DWL200 Instruments Mikrotechnik, Germany) that transferred the computer predefined design onto the photoresist (Shipley Microposit S1800 Series)-coated wafer with ∼1 μm precision. After irradiation and development, the wafers were etched using DRIE (Alcatel 601E) with fluorine-based reagents, from 10 s to 6 min, depending on the desired height of the structures. Pillar-structured silicon substrates with tunable pillar top areas, pillar gap, and pillar top shapes were fabricated. After resist-stripping (Microposit Remover 1165), the substrates were cleaned using ethanol and acetone. The superhydrophobic and highly adhesive pillar-structured silicon substrates were formed by silanizing the silicon substrates with heptadecafluorodecyltrime-thoxysilane (FAS) in a decompression environment at room temperature for 10 min, and then heating them at 120 °C for 3 h, resulting in reproducibly homogeneous and highly hydrophobic surfaces. Then, the CA of water and oil had been measured. (The solvent of our QD solution is octane, and we also use the octane as the oil for CA measurement). Patterning of the QD Active Layer. At first, the substrate, which had previously been deposited on two functional films, were prepared and stored in a glovebox. Then, a 10 mg/mL QD solution was prepared with the solvent octane. Next, the silica micropillar structured templates were laid out on a horizontal desk. Using a microsyringe, 3 μL of the 10 mg/mL QD solution was dripped on the silicon template; over which the solution spontaneously spread in a semi-ellipse. A sandwich system was then manufactured by covering the silicon template with the ITO substrate containing the two functional layers, and the final specialized structure was kept at 80 °C, for 30 min. After this, we pierced the ITO substrate with the patterning QD microwire arrays and put it into the glovebox for the next procedure. Preparation of the Device Substrate and Finish the Devices. The patterned ITO glass substrates were submerged in staining gel mixed with acetone, methanol, and deionized water for 20 min; then subjected to UV−ozone treatment for 10 min. After this, the cleaned substrate was moved into the glovebox where it was held in an N2 environment. PEDOT:PSS was spin-coated onto the ITO substrates at 3000 rpm for 30 s, and then annealed at 120 °C for 20 min. The PEDOT:PSS film serves as the hole injection layer in the QLED luminescent device. Next, 1.5 wt % of 9,9-dioctylfluorene-coN-(4-(3-methylpropyl))diphenylamine (TFB) in chlorobenzene was prepared and spin-coated atop the PEDOT:PSS film in the N2 environment at 2000 rpm for 30 s. This HTL, situated atop the hole injection layer was then baked at 150 °C for 30 min; and the device was returned to the glovebox. After patterning of the QD luminescent layer via the asymmetric wettability template, ZnO nanoparticles were deposited onto the top layer of the device via spincoating at 2000 rpm for 45 s, and then annealed at 60 °C for 20 min. Finally, Al cathodes were deposited sequentially on the top of the ZnO layer using the deposition apparatus. The entire sequence will eventually be encapsulated into a QD light-emitting device.



CONCLUSIONS In summary, we developed and exploited a facile approach to utilizing the asymmetric wettability interface for regulating the liquid dewetting process and effectively applying it in assembling QD nanoparticles into large-area and long-range28524

DOI: 10.1021/acsami.9b08603 ACS Appl. Mater. Interfaces 2019, 11, 28520−28526

Research Article

ACS Applied Materials & Interfaces Characterization of the QD Microstructure and QLED Device. PL images and in situ observation image were taken by a fluorescence microscope (Olympus, BX53). An atomic force microscope (FastScanBio, Bruker, Germany) and scanning electron microscope (S4800, Hitachi, Japan) were used to image and observe the QD microstructure. The transmission electron microscopy (JEM2100, JEOL, Japan) image was used to assess the QD nanoparticles. The current−voltage−luminance characteristics were measured with a Keithley 236 source-measure unit and a Keithley 2000 multimeter coupled with a calibrated Si photodiode. The EL spectra of the devices were obtained using a Konica Minolta CS1000A spectroradiometer.



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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.9b08603. Optical image; CAs and comparison; in situ optical microscopy observation image; mechanism cartoon; PL image; temperature−time diagram; TEM image and absorbance image; AFM and corresponding height diagram; PL image and SEM image; and various data of QLEDs (PDF)



AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (B.H.). *E-mail: [email protected] (Y.W.). ORCID

Zuliang Du: 0000-0003-3563-599X Yuchen Wu: 0000-0002-3451-7062 Lei Jiang: 0000-0003-4579-728X Notes

The authors declare no competing financial interest.



ACKNOWLEDGMENTS The authors acknowledge the MOST of China (grant no. 2017YFA0204504), the National Natural Science Foundation (21703268 and 21633014), and Beijing Natural Science Foundation (2182081).



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