Chemical treatment assisted nanoprinting of nanocrystals and optoelectronic devices

Abstract

A method for assembling nanocrystal (NC) submicron structures involves dispersing an NC core material prepared with ligands in a non-polar solvent to form an ink. The ink is printed using an electrohydrodynamic process in which an inkjet printer applies a high voltage between the tip of the nozzle and the substrate so that the ink is ejected in the form of ultra-small droplets from a meniscus at the tip of the nozzle. Upon ejection of the ink, the substrate located on a movable platform is moved to deposit NC in the form of a wire structure that can be assembled layer by layer into a multi-layer NC microelectronic device. Nozzle movement or platform movement is controlled to create on-demand patterns and films having any shape. Ligand exchange is implemented after the printing process to cause electronic coupling between NC particles at room temperature, thereby achieving regulation of electrical properties and adjustment of photoresponsivity to infrared light.

Description

Technical Field

[0001] This invention relates to the printing of electronic and optoelectronic devices with nanoscale resolution, and more specifically to electrohydrodynamic printing of nanocrystalline structures using colloidal nanocrystalline inks. Background Technology

[0002] With the rapid development of Internet of Things (IoT) networks, wearable technologies, autonomous machines, and AR / VR devices, ubiquitous sensing and computing are becoming a reality. Each of these requires high-performance and application-specific (opto)electronic devices. [1,2] These customizable devices are achieved through engineered multi-material compositions, adaptability and on-demand manufacturing, and heterogeneous integration with unrestricted sublayers. Additive manufacturing, also known as 3D printing, is a promising approach for fabricating customized multi-scale dimensional device structures using desired ink materials. [3,4] Although stereolithography-based 3D printing has achieved submicron resolution and geometric complexity, inks remain limited to metal (oxide) polymer materials, and the end products are typically used for mechanical and optical applications. [5,6,11] Fully printed microelectronics for photocarrier transport and detection are not yet competitive in terms of the patterning and functionalization of semiconductor inks and the construction of multilayer device stacks.

[0003] PCT application WO2021-077045 discloses a rapid fluid assembly method for nanoscale and microscale printing, which utilizes photolithography to form patterns and uses hydrophilic / hydrophobic patterns to guide the deposition of nanomaterials with high specificity and selectivity. However, this method cannot fabricate multilayer device stacks.

[0004] US Patent Application Publication US20210242414 relates to a method for manufacturing printed electronic devices using multiple passivation. However, this method uses only organic inks that are less stable and unresponsive to infrared light.

[0005] To address these significant challenges, it is necessary to collaboratively develop a broadly tunable ink system and a universal printing-sintering mechanism. Colloidal nanocrystals (NCs) are ideal ink materials for printing electronic devices, as cost-effective solution processing methods have demonstrated successful device integration in flexible circuits, photodetectors, and photovoltaics. NCs consist of ligand-shell-encapsulated nanocrystal nuclei, exhibiting a wide range of designable material properties. The semiconductor family of NCs is also known as quantum dots (QDs) and is highly regarded for its size-dependent photoelectric properties. Simultaneously, chemical processing or electrohydrodynamic printing (EHDP) is often employed to replace or remove insulating long-chain organic ligands on the NC surface with compact ligands, achieving electronic coupling of NC arrays. Selective ligand reagents further alter the carrier mobility and lifetime, doping type and concentration, and energy level positions of NC assemblies to construct complex device architectures through layer-by-layer coating of NCs. [18,19] also reported multilayer deposition strategies that can fill and smooth micron-scale voids and cracks caused by the volume loss of organic ligands during solid-state ligand-exchange (LE) processes.

[0006] Recently, 3D-printed NC or nanoparticle structures with nanoscale resolution have been achieved through various external field-assisted assembly methods. For example, charged metal particles are deposited into 3D nanostructures guided by flow fields and predefined electric fields. [12,13] Laser-induced hydrogel polymerization and sintering mechanically assemble metal nanoparticles to achieve linewidths as low as 20 nm.

[14] Photosensitive ligands form chemical bonds to locally connect NCs after two-photon laser initiation, thereby expanding the library of inorganic NC inks that can print patterns.

[15] However, these examples still depend on specific NC types and / or ligand matrices, making it difficult to satisfy the fully tunable physical properties that metallic, semiconductor, and dielectric NCs provide for solid-state device construction.

[0007] Electrohydrodynamic printing (EHDP) is an inkjet printing technology that supports a wide range of ink materials and ultra-high printing resolutions down to the nanoscale, exceeding nozzle diameter limitations. [7,8,9,10] EHDP's nanodroplet mode enables nanoscale metallic NC structures, but the high-temperature sintering process can degrade some semiconductor NCs and flexible substrates with low thermal resistance. It has also been reported that combining EHDP with low-temperature post-printing chemical treatments allows semiconductor NC / QD deposition on graphene as a sensitizer to enhance infrared (IR) photodetectors. However, existing techniques have failed to disclose how to fine-tune NC surface ligand interactions during EHDP and achieve multi-material and multi-layer printing for more scalable, fully printed NC optoelectronic devices. Summary of the Invention

[0008] This invention relates to a ligand exchange (LE)-assisted EHDP strategy for assembling submicron nanocrystal (NC) structures, followed by in-situ room-temperature chemical modification and functionalization to achieve layer-by-layer printing of NC microelectronic devices. The versatility of this method is demonstrated by combining multiple model NC systems (including but not limited to Ag NC, Au NC, PbS NC, CdSe NC, ZnO NC, and InSbNC) with a range of ligand reagents.

[0009] After initiating the LE process with compact ligands, the printed NC patterns shrink and densify, reducing the printed linewidths of Ag NC and PbS NC on Si substrates to as low as 70 nm and 350 nm, respectively. LE-induced shrinkage stems from ligand volume loss and NC fusion, thereby improving the conductivity on the NC array. Using EHDP parameters, continuous Ag NC nanowires were assembled on both Si / SiO2 and polydimethylsiloxane (PDMS) substrates, fabricating wide-gamut color gratings, submicron electrode arrays, and open-ring metasurfaces. By co-designing the linewidth and inter-line spacing, the nanowires were further densely packed to produce high-fill-rate and crack-free micron-scale films. By correlating IR spectroscopy and morphological evolution, we investigated the dynamic interactions between NC and ligands during the EHDP process to promote grain growth in the LE-induced printed Ag NC films. Treatment with NH4SCN (sometimes abbreviated as "SCN" in this paper) ligands resulted in Ag NC micron-sized films with a thickness of 1.99 × 10⁻⁶. 7 High DC conductivity of S / m. Finally, the micron-sized PbS NC film was printed using iodide and mercapto-based LE treatment and exhibited photoelectric properties comparable to spin-coated films. We successfully obtained fully printed PbS NC IR photodiodes with a pixel size of 10 μm and fully printed PbS NC / ZnO NC IR photodiodes with a pixel size below 10 μm by integrating these semiconductor NC and n-doped and p-doped LE treatments through multilayer and multi-ink printing. The printed asymmetric metal contacts enhanced the diode rectification behavior, resulting in lower dark current and faster light response at 1500 nm. Attached Figure Description

[0010] This patent or application document contains at least one color drawing. Upon request and payment of the necessary fees, the Patent Office will provide a copy of this patent or patent application publication with color drawings.

[0011] The above and other objects and advantages of the invention will become more apparent when considered in conjunction with the following detailed description and accompanying drawings, wherein similar names denote similar elements in various views, and wherein:

[0012] Figure 1A The components of an electrohydrodynamic printer (EHDP) are shown. Figure 1B This is a schematic diagram of the presynthesis of NC with oleic acid ligand-terminated structure and its use as a dispersion for printable ink. Figure 1C This is a diagram illustrating the EHDP process for depositing NC ink. Figure 1D This is a schematic diagram of the LE process. Figure 1E This is a schematic diagram illustrating the morphological changes of the pattern printed after LE (Loop Electrode) printing. Figure 1F This is a schematic diagram of adjacent non-nuclear cells (NCs) after LE (leukogenesis) using various compact ligand reagents. Figure 1G These are SEM images: The right image shows the SEM image of the printed AgNC membrane (right) deposited after treatment with NH4SCN ligands, and the left image shows the SEM image of the freshly printed AgNC membrane (left). Figure 1H Is with Figure 1G The same area at 2900cm -1 Images of nano-FTIR absorption mapping at wavenumbers, Figure 1I Is Figure 1G Nano-FTIR spectra obtained in two regions, Figure 1J The image shows SEM images of the Ag NC line after printing (left) and NH4SCN LE. Figure 1K The image shows SEM images of the PbS NC lines after printing (left) and after TBAI LE. Figure 1L These are images of the linewidths of these printed Ag and PbS NC lines before and after the LE (Extended Line Length), and... Figure 1M SEM images (top) and EDX element maps (bottom) of printed Ag, PbS, CdSe and ZnO NC patterns with different shapes are shown.

[0013] Figure 2A This is a diagram illustrating the deformation mechanism of AgNC lines printed after LE (Extended Line Layout). Figure 2B This is a graph showing the relationship between the pulse voltage amplitude and the line thickness after LE (Electrical Extension). Figure 2C A graph showing the relationship between pulse voltage amplitude and line width after LE is presented. Figure 2D The image shows the LE and a magnified print of the Hilbert curve. Figure 2E The graph shows the relationship between print speed and AgNC pad fill rate after LE effect. Figure 2F The deformation mechanism of Ag NC pads printed after LE is demonstrated. Figure 2G The images show AFM (left) and SEM (right) micrographs of Ag NC pads printed at different voltages after LE. Figure 2HThe relationship between pulse voltage amplitude and FR of Ag NC pads is shown. 2I shows the width of Ag NC lines printed at 350V pulse voltage and various print speeds before (pink) and after (purple) the same NH4SCN LE process. Figure 2J The image shows the height of Ag NC lines printed at 350V pulse voltage and various printing speeds before (pink) and after (purple) the same NH4SCN LE treatment. Figure 2K The aspect ratio of Ag NC lines printed at different printing speeds v and pulse voltages V is shown after the LE (extension line) versus before the LE (extension line).

[0014] Figure 3A This is a diagram illustrating the ligand desurfacing kinetics in a nozzle with the original ink concentration and a nozzle tip with a partially increased concentration. Figure 3B The results of FEM simulations of the LE process for particles with different diameters and diffusion coefficients are shown. Figure 3C This is a bar graph showing the grain size of Ag NC after LE printing using different initial ink concentrations. Figure 3D SEM images of Ag NC after LE printing with various original ink concentrations of (i) 3 mg / ml, (ii) 3.5 mg / ml, (iii) 4 mg / ml, and (iv) 8 mg / ml are shown. Figure 3E The nano-FTIR spectra of Ag NC pads printed after LE with different original ink concentrations are shown. Figure 3F Bar graphs showing the conductivity of Ag NC pads printed after LE with different initial ink concentrations are presented. Figure 3G It is a chart comparing conductivity with printing accuracy and post-processing temperature in related studies;

[0015] Figure 4A This is an illustration of SC generated through printing a raster structure. Figure 4B Optical and SEM images of RGB SC printed with various grating spacings of “E” shape are shown. Figure 4C This demonstrates more SCs created by programming the line spacing or mixing different proportions of RGB SCs. Figure 4D It shows Figure 4C The chromaticity coordinates of these representative SCs on the CIE 1931 chromaticity diagram. Figure 4E This is an illustration of a printed microelectrode array used for single-cell monitoring. Figure 4F This is an illustration of a printed metasurface that resonates at sub-THz wavelengths. Figure 4G SEM images of the printed microelectrode array are shown, as well as Figure 4H SEM images of the printed sub-THz metasurface are shown;

[0016] Figure 5A This is a diagram illustrating the structure of a PbS-Ag NC IR photoconductor. Figure 5B A graph showing the normalized absorbance of various ligand pairs for the wavelengths of printed and spin-coated PbS NC LE is presented. Figure 5C This is a graph showing the response rates of various ligands excited by 1480nm light to printed and spin-coated PbS NC LE. Figure 5D This is an illustration of the structure of a printed stack of PbS IR photoconductors printed using 950nm PbS NC and 1550nm PbS NC. Figure 5E A graph showing the absorbance as a function of wavelength in the printed stacked PbS IR photoconductor is presented. Figure 5F The transient photocurrent of a stacked photoconductor is shown under repeated on / off illumination at a frequency of 1 Hz and an applied voltage of 5 V. Figure 5G This is a diagram illustrating the structure of an Au NC-PbS-Ag NC IR photodiode. Figure 5H These are the energy band diagram, micro-optical diagram, and EDS image of a fully printed IR photodiode. Figure 5I and Figure 5J The responsivity of photodiodes printed using 1550nm and 950nm PbS NC is shown respectively; Figure 5K The transient photocurrent of a stacked photodiode is shown under repeated on / off illumination at a frequency of 1 Hz and an applied voltage of 5 V. Figure 5L It shows that in linear (V) D =-2V) and saturation (V D =-30V) The solution utilizes TBAI LE's printed PbS NC phototransistor in the dark (black) and is subjected to 2.5mW / cm 2 Io excited by 1480nm light (red) D -V G curve; Figure 5M A schematic diagram of the device architecture for a fully printed PbS NC / ZnO NC IR photodiode; Figure 5N This is the IV characteristics of a fully printed 1500nm PbS NC / ZnO NC IR photodiode in the dark (black) and under 1480nm illumination (red). Detailed Implementation

[0017] This invention establishes a nanoscale resolution printing method based on electrohydrodynamic printing (EHDP) to deposit inks from a library of colloidal nanocrystals (NCs), followed by in-situ room-temperature ligand exchange to functionalize the NC solids. This versatile method enables layer-by-layer printing using a wide selection of NC inks, ligand reagents, substrates, and device architectures. Chemically induced shrinkage and densification result in a minimum linewidth of 70 nm and a maximum film fill factor of 75% for the printed Ag NC structures. This is close to the conductivity of bulk Ag, enabling the construction of wide color gamut color gratings. By utilizing Ag, Au, PbS, and ZnO NCs and compact ligands such as TBAI, EDT, and NH4SCN, fully printed multilayer infrared photodiodes with pixel sizes below 10 μm were demonstrated. The nanoprinting and assembly of heterogeneous NCs holds promise for the easy integration of multifunctional micro / nano devices.

[0018] 1A illustrates components of an electrohydrodynamic printer (EHDP) for micron-nanometer scale printing. It includes a microscope 10 with a CMOS camera, a motion system 12, a pulse generator 14, an amplifier 16, and a computer control unit 18. The motion system 12 includes a substrate movement platform capable of moving a substrate 11 in the XYZ directions and two tilting displacement platforms. A micropipette 13 filled with colloidal NC ink is fixed to a stationary holder 15. The pulse generator generates electrical pulse signals, and the amplifier amplifies these signals, such that their range is -1000V to 1000V. Alternatively, the holder can be movable while the platform is fixed. In either case, the relative movement between the pipette and the platform is controlled by a computer via a drive motor 19 to print a specific pattern, which can be a series of overlapping layers to form a 3D structure.

[0019] Stable inks compatible with the EHDP process are formed from colloidal NCs capped with long organic ligands. For example... Figure 1B As shown, various NC core materials, including metals, semiconductors (also known as QDs), and metal oxides, are prepared using oleic acid (OA) or oleylamine (OLAM) surface ligands well dispersed in nonpolar solvents such as dodecane. The printing kinetics follow the previously reported EHDP study, where the power generated by the pulse voltage generator 14 and amplifier 16 is sufficient to overcome the surface tension and viscosity of the ink, allowing ink droplets to be ejected from the meniscus at the nozzle tip onto the substrate 11. Figure 1C As demonstrated, NC is deposited onto a substrate in the form of a line structure by moving the platform of an EHD printer in one direction. These printed lines, as basic elements, can be further arranged and combined to create on-demand patterns and films of arbitrary shapes by programming the trajectory of the moving platform.

[0020] However, these newly printed NC structures are electrically insulating because the individual NCs are separated by large-volume organic ligands. Figure 1B Therefore, compact ligands that dissolve in polar solvents, such as ethylene dithiol (EDT), NH4SCN, and tetrabutylammonium iodide (TBAI), have been introduced to replace long organic ligands. Figure 1F Similar to solid-state ligand exchange (LE) used in large-area NC films, a solution containing compact ligands is applied to cover the entire printed structure for 30-120 seconds, followed by multiple rinsing steps. Figure 1D As a result of the LE process, the interparticle distance is significantly reduced by removing or replacing long ligand molecules with compact ligands. These chemical reactions are thermodynamically favorable, thus eliminating the need for high temperatures. The substantial volume loss and changes in NC surface energy during the LE process after printing drive NC rearrangement, even partial fusion within the printed assembly, resulting in observable structural changes and alterations in physical properties. Figure 1D Ag NC ink and NH4SCN LE treatment were selected as model systems to further investigate the mechanism of the LE-assisted EHDP method.

[0021] The effectiveness of NH4SCN LE on EHD-printed Ag NC was verified using nano-FTIR technology, in which spatially resolved FTIR spectra can be collected at the AFM tip and scanned over the area to be mapped, while simultaneously measuring the AFM morphology. At a high NH4SCN concentration of 10 mg / mL, conditions typically used for large-area spin-coating of NC films, severe deformation and discontinuities were observed in the printed Ag NC lines. However, when the ligand concentration was reduced to 1 mg / mL, the structural and shape integrity of the printed NC solids was maintained, while the organic ligands were still effectively removed. An OA-terminated Ag NC layer was printed on top of the NH4SCN-exchanged Ag NC layer for side-by-side comparison of its morphology and IR spectra. Figure 1G and 1H The consistency between the SEM images and the nano-FTIR images is shown. The color contrast in the SEM reflects the difference in conductivity and z-height between the two regions of the printed Ag NC film. Figure 1G ), while nano-FTIR images show that at approximately 2900 cm⁻¹ -1 The intensity of IR absorption varies significantly at different wavenumbers. Figure 1H ).

[0022] exist Figure 1IIn the image, FTIR absorptions collected locally from freshly printed Ag NC films and LE-treated Ag NC films are superimposed, indicating that the CH stretching characteristic of the organic ligands completely disappears after NH4SCN treatment, thus demonstrating that the LE reaction was completed using a 1 mg / mL NH4SCN solution. Therefore, after LE treatment, the surface chemistry of the NC is reversed from nonpolar to polar. This orthogonal surface polarity minimizes redissolution during continuous deposition of the NC layer, thereby ensuring a clear edge of the Ag NC layer printed on top of the NH4SCN-treated Ag NC layer. Figure 1G and 1H This layer-by-layer printing method, utilizing alternating NC deposition and LE processing, allows for increased film thickness by constructing multilayer stacks. Figure 1E It should be noted that points with high FTIR absorption still exist on the ligand-exchanged Ag NC layer, consistent with the voids formed due to LE. The higher CH stretching signal originates from the self-assembled monolayer coating on the Si substrate beneath the AgNC film.

[0023] Under these optimal LE conditions (1 mg / mL NH4SCN or TBAI solution and a processing time of 60 s), volume shrinkage and linewidth reduction were observed in the printed NC lines. The width of the Ag NC line printed at 3 μm / s decreased from 651 ± 49 nm at printing to 274 ± 65 nm after NH4SCN LE. Similarly, the width of the PbS NC line printed at 3 μm / s shrank from 754 ± 65 nm at printing to 544 ± 34 nm after TBAI ligand exchange. Figure 1J-1L As shown. The length difference between OA and NH4SCN or TBAI ligands resulted in a reduction of about 1 nm, equivalent to 20% of the grain size. The more significant shrinkage of the printed Ag NC microstructure can be attributed to the further densification of Ag NC by NC sintering and local grain growth during the LE process. The densification effect is different from that observed in large-area NC films treated by LE, where adjacent NCs fuse into larger grains, but usually leave cracks and voids between these grains. The resulting NC films are porous and even discontinuous, requiring multiple layers of NC deposition to fill the voids and achieve high conductivity.

[21] However, since the EHDP linewidth is reduced to a scale similar to the grain size of chemically sintered NC, the fusion of printed NCs only results in uniform shrinkage and densification within the printed line without the formation of obvious cracks.

[0024] Therefore, this LE-assisted EHDP method enables the assembly of NC-printed materials into submicron solids and their electronic coupling at room temperature. The printed Ag NC lines and films achieved conductivity up to approximately 10% of bulk Ag, and the printed PbS NC films were functionalized to construct IR photodetectors with performance comparable to spin-coated devices. In addition to Ag and PbS NC, LE-assisted nanoprinting is generally applicable to other NC inks, including CdSe NC and ZnONC, as demonstrated with NH4SCN ligand exchange, to achieve a variety of pattern designs at submicron resolution. Figure 1I ).

[0025] therefore, Figure 1A-1M This demonstrates NC's LE-assisted nanoprinting. Specifically, Figure 1B This is a schematic diagram of the presynthesis of NC with oleic acid ligand end capping and its dispersion as a printable ink. Figure 1C This is a diagram of the EHDP process for depositing NC ink. Figure 1D A schematic diagram of the LE process is shown. Figure 1E The morphological changes of the pattern printed after LE are shown. Figure 1F A schematic diagram of adjacent non-nuclear zones (NCs) after LE using various compact ligand reagents is shown. Figure 1G In the image, the right side shows a SEM image of the printed Ag NC film (right) deposited with NH4SCN ligand, and the left side shows a SEM image of the freshly printed Ag NC film (left). The SEM images are shown in the following scale: 1 μm in the main image and 200 nm in the magnified image. Figure 1H It shows the relationship with Figure 1G The same area at 2900cm -1 Nano-FTIR absorption mapping at wavenumber. Figure 1H It shows in Figure 1G Representative nano-FTIR spectra obtained in the two regions shown. Figure 1I Is Figure 1G Nano-FTIR spectra obtained in two regions, in Figure 1J The image shows SEM images of the Ag NC line after the initial printing (left) and the NH4SCN LE. Figure 1K SEM images of the PbS NC lines after printing (left) and after TBAI LE are shown. Scale bar is 1 μm. Figure 1L The linewidths of these printed Ag and PbS NC lines are shown before and after the LE (Extended Linear Array). Figure I shows SEM images (top) and EDX element maps (bottom) of the printed Ag, PbS, CdSe, and ZnO NC patterns with different shapes. Scale bar, 20 μm. Figure 1MThe image shows SEM images (top) and EDX element maps (bottom) of printed Ag, PbS, CdSe and ZnO NC patterns with different shapes.

[0026] Formation as Figure 1B The continuous lines with densely packed NC, as shown, are essential for constructing other 1D and 2D pattern geometries with fewer defects and excellent electrical and optoelectronic properties. As described above, using Ag NC ink and NH4SCN LE treatment with a fixed nozzle outer diameter of 4 μm as a model system, the effects of printing parameters (i.e., ink concentration, platform speed, and pulse voltage) on determining the printed morphology can be investigated. Semiconductor Si with a thin layer of natural SiO2 was used as the substrate to avoid the autofocusing effect observed on highly conductive metal substrates and the repulsion effect caused by charged particles printed on insulating substrates, both of which alter the morphology of the printed lines.

[0027] The freshly printed Ag NC structure contains both an Ag NC core and OA ligands. In previous studies of EHDP metal nanoparticles, bulk polymers such as the diblock copolymer P2VP-b-PEO were grafted onto the surface of the metal nanoparticles as stabilizers. The change in printing mode from nanodrop to spray is highly sensitive to the applied voltage, which is well described by a theoretical model assuming constant printing viscosity. However, compared to polymer matrix encapsulation, the coordination of OA ligands on the NC surface is in dynamic equilibrium and less stable. Therefore, the local concentration, viscosity, and dielectric constant of the NC ink can vary drastically at the nozzle tip, making the amount of Ag NC deposited per unit print length dependent on the applied voltage and platform movement speed. SEM images and EDX mapping confirm that more Ag NC is printed per unit print length as the pulse voltage increases and the platform movement slows down.

[0028] Variations in Ag NC content per printed length result in different line morphologies after the LE process. The effects of pulse voltage and plateau speed on the thickness and width of the printed Ag NC lines were systematically investigated. Figure 2B As shown.

[0029] However, after NH4SCN LE processing, the final line width of the printed NC lines does not change monotonically, such as... Figure 2CAs shown, when the platform speed remains constant but the voltage increases, the linewidth initially increases below 350V as more Ag NC is deposited per second, then decreases above 400V due to the transition from dripping to jetting mode in EHD mode. When the voltage is fixed and below 300V, the nano-drip mode dominates, causing the linewidth to increase initially and then decrease with platform speed. When the constant voltage is increased above 350V, it follows the jetting mode behavior, resulting in a faster printing speed and thus a narrower linewidth.

[0030] Based on the above controlled experiments, when the Ag NC ink concentration was 1.3 mg / ml and the nozzle outer diameter was 2 μm, the optimal pulse voltage and plateau speed for printing nanowires were 300 V and 5 μm / s, respectively. Integrating these conditions with the LE parameters (immersion in 1 mg / mL NH4SCN solution for 60 seconds), the minimum linewidth of Ag NC printed on Si substrates reached 70 nm without utilizing the autofocus effect. It can be demonstrated that LE-assisted printing of continuous Ag NC lines can form 90 × 90 μm nanometers. 2 Or 50×50μm 2 The quartic fractal Hilbert curve ( Figure 2D ) or 200×200μm 2 Or 150×150μm 2 Other fractal orders. The pattern is printed in one go, with a uniform linewidth of 400 nm and a thickness of less than 100 nm on straight paths and 90° turns.

[0031] Printing gapless line arrays to form dense thin films is the next crucial step in building optoelectronic devices. NC (non-conductive) printing involves moving a platform forward and backward while maintaining a certain spacing between two parallel lines. Newly printed NC lines are non-conductive and have a finite dielectric constant, disrupting the surrounding electric field distribution and hindering the further printing of subsequent lines. Therefore, the spacing between adjacent printed lines and the width of the printed lines must be co-designed to minimize inter-line interference while achieving a high packing density of the line array, and thus a high filling ratio (FR) of the printed Ag NC film.

[0032] Since the organic ligands are removed after the LE process, the FR of the printed film is the area occupied by the bare NC on the total printed area. With the same line spacing, the FR is determined by the platform speed v and the pulse voltage V. Furthermore, multiple NC layers can be printed in the same area to increase the packing density. Effective speed v e =v / l N It can be defined as being related to the total amount of NC deposited per unit time, where l NThis indicates the number of printed layers. By analyzing the relative area of ​​the bare Ag NC pads in the SEM image, the FR (Flat Area) of the NH4SCN-treated Ag NC pads printed at a fixed 500V can be calculated. This shows the effect of v... e Increased from 2.5 μm / s to 10.0 μm / s Figure 2E (Green line), the fill rate decreased linearly from 75±5% to 20±1%. However, the measured FR was higher than that from v e The relative FR (derived from the inverse proportional relationship) Figure 2E (yellow line), especially in the middle v e This deviation indicates that the first Ag NC layer, although printed at a higher v, was dense enough to maintain a higher FR, thus allowing for the use of fewer additional layers or even higher v. e To achieve the same FR.

[0033] Based on the amount of Ag NC deposited per unit length, three morphological transformation modes were observed during the removal of all organic ligands and NC fusion on printed Ag NC via NH4SCN LE treatment. As shown in the top row of Figure 2a, the printed Ag NC lines are thick and wide when v is low and V is high. LE in these structures causes significant volume shrinkage, resulting in nanopores both internally and on the surface. In contrast, excessively fast v and excessively low V result in insufficient Ag NC deposition to compensate for the voids generated by the LE process, leading to crack formation in the NC film (Figure 2a, bottom). Therefore, there are optimal printing parameters when the Ag NC lines become dense along the direction perpendicular to the printing direction (i.e., along the line width) after LE without leaving pores or cracks. For continuous Ag NC lines, a minimum linewidth of 70 nm can be achieved by LE-assisted nanoprinting on a semiconductor Si substrate. To further understand the correlation between linewidth and height printed before and after LE, Ag NC lines printed at different v at 350 V were selected and analyzed. Figure 2I As depicted, the linewidth decreases with increasing v because the number of ink droplets and the amount of Ag NC deposited per unit length decrease. Therefore, the LE process further shrinks the linewidth, but the relative size change varies with v. When v exceeds 6.0 μm / s, the linewidth of freshly printed Ag NC is less sensitive to velocity changes, and the reduction caused by LE is small due to insufficient Ag NC for migration and fusion, corresponding to the third mode in Figure 2a. Similarly, the line height also decreases with increasing v. Figure 2JFor structures with printing speeds below 2.5 μm / s, the line height reduction after LE is less than 10%. When v exceeds 4.0 μm / s, the height difference increases and becomes approximately constant, indicating the transformation mode shift described in Figure 2a. Since LE can modify line width and height differently, it is necessary to statistically study the aspect ratio (line height / width, H / W) after LE relative to the aspect ratio before LE, i.e., the relative aspect ratio (RH / W). RH / W = 1 indicates that the Ag NC line shrinks simultaneously in width and height, while RH / W < 1 (or RH / W > 1) indicates that the height (or width) is reduced more than the width (or height). Figure 2I and Figure 2J In the analysis, RH / W is a function of both v and V. We only plot points where RH / W is greater than 0.8 to highlight the transition points. Figure 2K As V increases from 250V to 600V, the transition point of RH / W≈1 first shifts to the lower V and then to the higher V, indicating a change in the EHDP mode. This RH / W analysis provides a detailed reference for parameter selection to guide morphology-specific printing fabrication. It was also found that the pulse voltage V affects the morphology and FR of the printed Ag NC film. At a constant V of 5 μm / s... e When V approaches the critical voltage of 250V, the freshly printed film contains a large portion of voids, which become micropores after LE-induced Ag NC sintering. Figure 2F and 2J (See the top figure). At such low V, the linewidth is less than the 400 nm spacing between printed lines, leaving unfilled spaces. Furthermore, due to the limited overall Ag NC content, the volume shrinkage resulting from organic ligand removal and Ag NC chemical sintering cannot be compensated for. The resulting crosslinked Ag NC network is highly porous with a low FR of less than 10%. Increasing V from 250V to 650V results in smoother and less porous printed Ag NC films due to wider linewidths and higher Ag NC content per printed area. Figure 2F and 2J (See the middle figure). However, when V is high enough to print too much Ag NC per unit area, a wavy surface structure was observed on the printed Ag NC film after LE, in which longitudinal cracks 5 μm wide were formed along the printing direction. Figure 2F and 2J (See the bottom image). This phenomenon is consistent with previously reported spin-coated thick NC films. In v e With the line spacing fixed at 5 μm / s and 400 nm, respectively, the quantitative relationship between pulse voltage and FR was investigated. Figure 2HAs shown, the FR of the printed Ag NC film increases with increasing V, reaching a certain value after V = 550V. However, after NH4SCNL-E treatment, the FR increases monotonically as V changes from 250V to 650V, but begins to decrease when V is greater than 650V, which is consistent with... Figure 2F The description is consistent with that in the text.

[0034] Figure 2A-2K The effect of printing parameters on the morphology of NC patterns is shown. Figure 2A The deformation mechanism of AgNC lines printed after LE is shown. Figure 2B The relationship between the pulse voltage amplitude after LE and the line thickness is shown. Figure 2C The relationship between the pulse voltage amplitude and line width after LE is shown. Figure 2D The image shows the LE and the Hilbert curve after local magnification. Scale bars: 5 μm and 500 nm. Figure 2E The effect of print speed after LE is shown in relation to the fill rate of AgNC pads. Scale bar: 200nm. Figure 2F The deformation mechanism of AgNC pads printed after LE is shown. Figure 2G AFM (left) and SEM (right) micrographs of AgNC pads printed at different voltages after LE are shown. Scale bars: 1 μm (left) and 2 μm (right). Figure 2H The diagram shows the relationship between the pulse voltage amplitude and the FR of the AgNC pad before and after the NH4SCN LE treatment. Figure 2I shows the width of the AgNC line printed at a 350V pulse voltage and various print speeds before (pink) and after the same NH4SCN LE treatment (purple). Figure 2J The image shows the height of Ag NC lines printed at 350V pulse voltage and various printing speeds before (pink) and after (purple) the same NH4SCN LE treatment. Figure 2K The figure shows the aspect ratio (height / width, H / W) of Ag NC lines printed at different printing speeds v and pulse voltages V after LE, relative to the aspect ratio before LE (i.e., relative aspect ratio RH / W). The darkness of the dots corresponds to the value of RH / W. ​​Cases where RH / W is less than 0.8 are omitted in the figure.

[0035] Room temperature chemical sintering of printed Ag NC was considered. LE treatment induces chemical sintering and grain growth of NC, resulting in high conductivity of spin-coated Ag NC films

[17] . When chemical treatment is applied to nanoprinted NC structures, the LE-induced grain size evolution is more sensitive to the ink concentration used in the EHDP process. Five different ink concentrations were used to print 50 × 30 μm NC structures. 2Ag NC films with ink concentrations of 2.0 mg / ml, 3.0 mg / ml, 3.5 mg / ml, 4.0 mg / ml, and 8.0 mg / ml were obtained. They underwent the same NH4SCN LE post-treatment, but when the ink concentration increased from 2.5 mg / ml to 8.0 mg / ml, the average grain size of the LE-treated printed Ag NC films extracted from SEM images decreased from 73.3 ± 20.9 nm to 25.9 ± 4.0 nm. Figure 3C and 3D The effect of the pulse voltage is minimal, as the same results were obtained when V was increased from 350V to 800V. Therefore, the variation in grain size for different ink concentrations stems from differences in the thermodynamic driving force and kinetic rate of NC grain growth, indicating that this is modulated by ligand NC surface bonds and NC grain size.

[0036] To investigate the effect of the EHDP process on NC surface ligands, nano-FTIR was used to detect organic ligands attached to Ag NC films. It was determined that the CH signal detected from freshly printed Ag NC films decreased with increasing ink concentration. Figure 3E At an ink concentration of 4.0 mg / ml, near-zero IR absorption of CH fingerprints was observed at large aggregation sites formed in the freshly printed Ag NC film. Figure 1G A comparison was made between freshly printed and LE-treated Ag NC patterns. The freshly printed pattern exhibited higher IR absorption at the CH peak due to the presence of ligands; however, after ligand exchange, OA ligands detached, resulting in near-zero absorption at the CH peak. At high ink concentrations, OA ligands may aggregate and detach, leading to lower OA content in the unexchanged pattern, resulting in near-zero absorption at the CH peak. When printed with 8.0 mg / ml ink, no IR absorption was detected across the entire surface of the Ag NC film. These observations indicate that the EHDP process at high NC concentrations leads to the separation of organic ligands. Figure 3A As demonstrated, when NCs are squeezed together in high-concentration NC ink, some organic ligands may leave the NC surface

[23] , resulting in irreversible NC agglomeration. This process is more likely to occur at the 3 μm nozzle tip, where solvent evaporation and high electric field strength attract NCs and result in localized high ink concentrations. As the aggregated NCs move along the electric field lines, the stripped or loosely bound organic ligands move in the opposite direction, thus further promoting ligand separation during the evaporation of the fixed droplets.

[24] Large aggregation sites in printed Ag NC films can be effectively reduced by shortening the fixed droplet evaporation by increasing the platform velocity from 5 μm / s to 10 μm / s. Due to the lack of a high electric field associated with EHDP, the formation of NC aggregates and reduced organic ligand coverage have not been specifically reported in conventional inkjet-printed NCs.

[0037] Modification of the NC surface ligands during EHDP directly affects LE-induced sintering after printing. Based on the inventors' previous research in the CuNC paper, it is known that LE with organic ligands induces ligand compression, which reduces the interparticle distance and generates a high chemical potential, thereby driving NC fusion. The results show that NH4SCN has a moderate affinity for Ag. When LE is performed with NH4SN, surface Ag atoms can diffuse onto the Ag NC to grow larger grains without the obstruction of an OA shell, but the grain size is limited to approximately 100 nm, consistent with observations. Figure 2I The results show that smaller NC diameters are beneficial for fusion and grain growth processes. The LE chemical sintering process is qualitatively described by the Alan-Chan equations [25,26], where the specific surface area (SSA, surface area / volume) determines the diffusion coefficient of Ag atoms and the available free energy released during the LE process. The SSA of the agglomerated particles (approximately 200 nm) found in the printed concentrated NC ink was several times smaller than that of the original Ag NC (approximately 4 nm). Consistently, numerical simulations of this model show that, after the same LE reaction time, smaller diameter particles are more likely to aggregate than larger particles, resulting in a higher packing density. Figure 3B Therefore, by correlating IR results with numerical calculations, it is concluded that during EHDP of high-concentration NC inks, a significant portion of the organic ligands are lost, resulting in the formation of larger Ag NC aggregates during printing, which provides a limited driving force for the subsequent LE chemical sintering process.

[0038] The direct current (DC) conductivity was measured by printing Ag NC films onto two pre-evaporated Au electrodes. Since the grain size increases with decreasing ink concentration, the conductivity reaches its highest value at an ink concentration of 3.0 mg / mL. Figure 3F By treating the printed Ag NC film with NH4SCN solution at room temperature, the insulating film was transformed to have a conductivity of 1.78 × 10⁻⁶. 7 The conductivity of the membrane with a strength of S / m can be further increased to 1.99 × 10⁻⁶ by briefly immersing the membrane in an aqueous NaBF₄ solution to reduce surface oxidation of Ag₂NC. 7 S / m. Although the conductivity of the printed Ag NC film is comparable to that of a large-area spin-coated Ag NC film with the same ligands and chemical treatment, the LE-assisted nanoprinting method achieves submicron feature resolution, down to 70 nm on semiconductor Si substrates and down to 150 nm on insulating SiO2 substrates. Figure 3GThe conductivity achieved according to this invention was compared with the conductivity of other Ag inks printed in the literature based on post-processing temperature and printing resolution, thus establishing a benchmark for the low-temperature chemical sintering and high conductivity of this invention for nanoscale and flexible device applications. Specifically, DC conductivity was measured using a four-point probe method, which involved measuring the conductivity of four Au electrodes defined by direct laser writing (Picomaster 200) and thermal evaporation to form a 2×2 array with a 5 μm gap between them. An Ag NC film (20 μm × 20 μm) was printed at the center of the four electrode pairs to ensure sufficient contact area between the sample and the electrodes. After the LE process, the sample was tested with a 1 mg / ml NH4SCN solution for 60 seconds and measured again after further reduction with a 25 mM NaBH4 aqueous solution for 90 seconds. The four-point probe conductivity measurements were performed using a probe station (CHPUIST ZH-4) and a source meter (Keysight B2902B). Calculate the sheet resistance R using the Van der Pauw equation. S : Where R 12,34 Through V 34 / I 12 Calculated, where V 34 A current I is applied between Au electrodes 1 and 2. 12 At that time, the voltage drop between Au electrodes 3 and 4. The same naming format applies to R. 23,41 Field-effect transistor (FET) devices are characterized using a standard three-terminal setup. Two probes are contacted with the source and drain, which are interfacing with the NC channel layer, and a third probe is applied to the degenerate p-doped Si common gate for gate bias. Measurements for FETs are performed using a probe station (CHPUIST ZH-4) and a source meter (Keysight B2902B).

[0039] As explained above, Figure 3A-3G The effect of ink concentration on ligand-NC adhesion and post-printing grain growth is shown. Specifically, Figure 3A This is a diagram illustrating the surface kinetics of ligand delamination in the nozzle of an ink jetter with the original ink concentration and in the nozzle tip with a partially increased concentration. Figure 3B Finite element method (FEM) simulation results are shown for LE-induced NC fusion processes with and without LE process (t=0) and with LE process (t=1) for particles with different diameters (small diameter: large diameter = 1:3) and diffusion coefficients. Figure 3C The grain size of AgNC after LE printing with various original ink concentrations is shown. Figure 3DSEM images of AgNC after LE printing with various original ink concentrations (i.e., (i) 3 mg / ml, (ii) 3.5 mg / ml, (iii) 4 mg / ml, (iv) 8 mg / ml) are shown. Figure 3E Nano-FTIR spectra of AgNC pads printed after LE with various original ink concentrations are shown. Figure 3F The DC conductivity of AgNC pads printed after LE with various original ink concentrations is shown. Figure 3G This is a comparison of conductivity with printing accuracy and post-processing temperature in related studies.

[0040] The nanometer-scale resolution and high conductivity of printed Ag NC lines can be used to construct grating-based structural colors (SCs). The grating structure diffracts incident white light into monochromatic light at specific angles and phases to produce various SCs. Figure 4A This technology holds promise for flexible displays, strain sensing, and anti-counterfeiting. LE-assisted nanoprinting was used to fabricate Ag NC linear arrays with a spacing range of 1900 nm to 600 nm at 100 nm intervals on ITO transparent substrates. Due to the precisely defined impurity-free and highly uniform morphology, the printed Ag NC gratings exhibit high-purity SC. Figure 4B SEM images of Ag NC for RGB SC are shown, printed with a linewidth of 320 nm and producing raster patterns with spacings of 2220 nm, 1720 nm, and 1320 nm, respectively. Compared to recent meniscus-guided printing of SC,

[27] the results of this invention achieve a wider color gamut ( Figure 4D This is attributed to narrower linewidths, more adjustable line spacing, and higher printing speeds up to 25 μm / s. By combining different line spacings within a single printed raster structure, the mixed SCs can be programmed according to the ratio of the basic RGB SCs, such as... Figure 4C As shown. For example, when three primary SC gratings are printed at an equal scale, white is observed.

[0041] In addition to line gratings, complex patterns with extended functionality can also be printed using high printing resolution and room temperature LE-assisted NC sintering. Figure 4E and 4G This demonstrates an Ag NC electrode array with submicron feature size suitable for single-cell monitoring and biosensing applications, while Figure 4F and 4H A metasurface consisting of subwavelength open-loop resonators that strongly interact with IR light is shown. Furthermore, these structures, including line gratings and microelectrode arrays, are sequentially printed onto PDMS films to demonstrate the compatibility of this room-temperature additive manufacturing method with flexible substrates.

[0042] therefore, Figures 4A-4H The application of nanoprinted Ag NC wires is shown, in which Figure 4A This is an illustration of the SC generated by the printed raster structure. Figure 4B Optical and SEM images of RGB SC printed with various grating spacings of 'E' shape are shown. Scale bar, 10 μm. Figure 4C More SCs are shown, created by programming the line spacing or mixing different proportions of RGB SCs. Figure 4D The chromaticity coordinates of these representative SCs on the CIE 1931 chromaticity diagram are shown, while Figure 4E This is an illustration of a printed microelectrode array used for single-cell monitoring, and Figure 4F An illustration of a printed metasurface resonating at sub-THz wavelengths is shown. Figure 4G SEM images of the printed microelectrode array are shown, as well as Figure 4H The printed sub-THz metasurface is shown. Scale bar, 10 μm.

[0043] This study demonstrates a fully printed multilayer PbS NC IR photodetector. IR-absorbing PbS NC is considered a building block for bottom-up construction of photodetectors (PDs). Although PbS NC IR PDs have been progressively improved through the development of chemical modifications targeting NC and / or stacking different functional layers, the pixelation of these spin-coated devices remains largely unexplored, especially below 100 μm pixel size. Therefore, LE-assisted nanoprinting was used to form micron-scale (below 10 μm) PbS NC patterns and PD devices. To verify the photoelectric properties of the printed PbS NC, the light response of the printed PbS NC film was first compared with that of the spin-coated PbS NC film. Using the optimized printing parameters described above, PbS NC with a first exciton absorption peak of 1500 nm was printed on an evaporated Au electrode pair with a 5 μm gap. Figure 5A The printed PbS NC film was subjected to LE treatment with EDT or TBAI ligand reagents. The photocurrent spectrum of the printed PbS NC film was very similar to that of a spin-coated PbS NC film with the same solid-state LE. Figure 5B A slight redshift and broadening of the photocurrent peak in the printed PbS NC film was observed, indicating improved electronic coupling and photocarrier delocalization on the printed NC array. The TBAI-treated printed PbS NC film exhibited high current in both darkness and under 1480 nm laser illumination. Figure 5C This is consistent with the behavior observed in spin-coated PbS NC films. Double-ended PbS NC photoconductors are printed on degenerate-doped Si with 300 nm SiO2, and the behavior is achieved through p...++ -Si and a third gate voltage are applied to one of the two electrodes, and the photoconductor can also operate as a field-effect transistor (FET). Figure 5A We measured the transfer characteristics of the printed PbS NC FET processed by TBAI. Figure 5L In darkness, due to exposure to air during device handling and measurement, PbS NC exhibits predominantly p-type behavior. Under 1480 nm monochromatic illumination, both on- and off-currents increase, while the on / off current ratio decreases. This is due to photogeneration in the PbS NC channel layer, V G The higher photocurrent at 0V to 40V is consistent with the higher hole concentration. PbS NC films can also be printed on pre-printed Ag NC electrodes to form fully printed PbS NC photoconductors and their arrays.

[0044] Next, the feasibility of printing multilayer PbS NC films was further demonstrated by stacking a PbS NC film with an absorption peak of 950 nm on top of a PbS NC film with an absorption peak of 1500 nm to construct a bilayer photoconductor. Both printed NC films were processed by TBAI after printing. The photocurrent spectrum showed contributions from both NC layers, even when the Au electrode was only in contact with the bottom NC film. Figure 5E and 5F This is consistent with the funnel effect previously reported in spin-coated PbS NC films, where photocarriers generated in wider bandgap and smaller NC layers can migrate to the bottom metal contact via hierarchical band alignment between NC layers. Although... Figure 5E As shown, when illuminated by 945nm light, the overall photocurrent of the 950nm PbS NC layer dominates, but the transient light response of the stacked NC photoconductor is more similar to that of a single-component 1500nm PbS NC photoconductor. Figure 5F This is consistent with the carrier transport mechanism dominated by the bottom layer in this bottom-contact geometry. These properties indicate that the photoelectric properties of the bottom PbS NC film remain unchanged after the top PbS NC layer is printed. If the order of the two PbS NC layers is interchanged, the top-down transport of photocarriers is blocked, resulting in the disappearance of the photoresponse at 1500 nm. These properties demonstrate that the photoelectric properties of the bottom PbS NC film are intact after the top NC layer is printed.

[0045] Inspired by the above findings, a fully printed PbS NC IR photodiode was developed. Instead of a single-type doped PbS NC photoconductor, the photodiode contains a pn junction, which can be established by employing different doping effects such as EDT and TBAI LE on the PbS-NC. Metal electrodes with higher and lower work functions, such as Au and Ag, are needed to reduce the Schottky contact barrier on the p-side and n-side, respectively. Therefore, to fabricate such multilayer and multimaterial device structures, Ag and Au films are printed to form a bottom electrode pair, both assisted by NH4SCN LE. A TBAI-treated PbS NC layer is printed on the Ag electrode, covered with an EDT-treated PbS NC layer, which is printed to connect to the Au electrode. Figure 5G and Figure 5I The overlapping region of the two PbS NC layers defines the pn junction. Figure 5G and 5H The final device printed with PbS NC electrodes with absorption peaks around 1500 nm exhibited rectification behavior in the dark. In contrast, the same PbS NC stack printed on symmetrical Au electrode pairs exhibited linear IV characteristics, with electron injection and extraction hindered by the PbS NC-TBAI / Au interface. The printed photodiode device showed a light response to 1480 nm illumination, with an EQE of 64.4%, while the dark current remained as low as 3.3 × 10⁻⁶. -10 A. However, as the illumination wavelength decreases, the IV characteristic becomes less rectified ( Figure 5J This indicates that the built-in potential becomes insufficient to modulate photocarriers generated by higher-energy photons. This phenomenon is less pronounced when using smaller PbS NCs with wider band gaps. Figure 5I The formation of depletion regions in photodiodes also reduces the response time from 300 milliseconds measured by photoconductor devices to less than 60 milliseconds. Figure 5K ).

[0046] Figure 5A-5N This relates to IR photodetectors based on multi-material nanoprinting utilizing ordered ligand exchange. Figure 5A This is a diagram illustrating the structure of a PbS-AgNC IR photoconductor. Figure 5B Normalized absorbance for wavelengths of printed and spin-coated PbS QD LEs for various ligand pairs is shown. Figure 5C The response rates of various ligands excited by 1480 nm light to printed and spin-coated PbS QD LEs are shown, while Figure 5D This is a diagram illustrating the structure of a printed stack of PbS IR photoconductors printed using 950nm PbS QD and 1550nm PbS QD. Figure 5E The absorbance variation with wavelength of the printed stacked PbS IR photoconductor is shown. Figure 5F The transient photocurrent of a stacked photoconductor under repeated on / off illumination at a frequency of 1 Hz and an applied voltage of 5 V is shown. From top to bottom: 945 nm light, 945 nm light from a single-layer photoconductor with a QD of 1550 nm, and 1480 nm light. Figure 5G This is a diagram illustrating the structure of an AuNC-PbS-AgNC IR photodiode. Figure 5H The energy band diagram, micro-optics diagram, and EDS image of the fully printed IR photodiode are shown. Scale bar: 10 μm. Figure 5I and 5J The responsivity of photodiodes QD printed using 1550nm and 950nm PbS are shown, respectively. Figure 5K The transient photocurrent of a stacked photodiode under repetitive on / off illumination at a frequency of 1 Hz and an applied voltage of 5 V is shown. Figure 5K The image shows, from top to bottom: EDT-PbS photoconductor, TBAI-PbS photoconductor, and photodiode. Figure 5L It shows that in linear (V) D =-2V) and saturation (V D =-30V) The PbS NC phototransistor printed by TBAIL-E was used in the dark (black) and was subjected to 2.5mW / cm 2 Io excited by 1480nm light (red) D -V G Curves, solid lines, and dashed lines distinguish forward and backward scanning, respectively.

[0047] However, the double-layer structure with asymmetric metal contacts still cannot guarantee a significant open-circuit voltage under illumination, even at shorter excitation wavelengths. Figure 5H The device operation is dominated by the photoconductor mode, rather than the photovoltaic mode of a photodiode. Therefore, we ultimately introduced ZnO NC as the n-type electron transport layer and realized a fully printed NC photodiode. Instead of vertically stacking active layers with at least one transparent top or bottom electrode in a typical photodiode structure, we fabricated the NC photodiode by printing and laterally stacking multiple layers on two bottom metal electrodes. Figure 5MThe diagram illustrates the device architecture of a fully printed PbS NC / ZnO NC IR photodiode. This photodiode contains sequentially printed Au NC-SCN / PbS NC-EDT / PbS NC-TBAI / ZnONC-SCN / Ag NC-SCN layers processed using corresponding LE (Electrical Engineering) techniques. Specifically, a pair of Au and Ag NC pads are printed with gaps and processed via SCN LE. Then, the PbS NC-EDT / PbS NC-TBAI / ZnO NC-SCN layers are sequentially printed, followed by corresponding LE processing, where a ZnO NC layer is deposited on top of the PbS NC layer, separating the PbS NC layer from the Ag NC electrode. Therefore, the complete conduction path is through the Au NC-SCN / PbS NC-EDT / PbS NC-TBAI / ZnO NC-SCN / Ag NC-SCN layers, which includes horizontal charge transport directions within each layer and vertical directions at the interlayer junction interfaces. We showcased this type of fully printed device with a photosensitive area pixel size of 30×15μm. 2 and 9×9μm 2 This resolution is comparable to that of state-of-the-art IR imagers. For 1500nm PbS NC, the fully printed NC photodiode exhibits rectified IV characteristics, with a dark current as low as 2.1 × 10⁻⁶. -12 A. Under 1480nm illumination, the device achieved an open-circuit voltage of 0.2V and an EQE of 56.1% at -4V. Figure 5N The relatively high EQE is also attributed to direct illumination on the PbS NC layer, without the absorption loss in the transparent top electrode.

[0048] Response rate (R) is defined as follows:

[0049]

[0050] Where P inc It is the power of the incident light in the effective region. Detectivity (D*) is defined as:

[0051]

[0052] Where R λ R is the wavelength λ, S is the effective area of ​​the channel, and q is the absolute value of the electron charge.

[0053] AgNC inks were prepared using Ag nanocrystals (AgNC) particles and dodecane, with concentrations ranging from 2 mg / ml to 8 mg / ml. The AgNC inks were ultrasonicated at 25°C for 5 minutes and then sprayed into nozzles. PbS, CdSe, and ZnO inks were prepared using the same methods as the AgNC inks, achieving concentrations of 5.5 mg / ml, 4 mg / ml, and 5 mg / ml, respectively.

[0054] By setting various combinations of heating temperature and pulling speed, capillary nozzles with an outer diameter of 2-4 μm can be manufactured using a micropipette puller (Sutter P-97).

[0055] A rigid substrate comprising SiO2, Si, and Si with an Au coating was ultrasonically cleaned in isopropanol for 5 minutes. The cleaned substrate was then further treated in oxygen plasma at 100 W and 0.5 mbar for 1 minute. A SiO2-Au electrode was fabricated by spin-coating 500 nm of Au and 10 nm of Cr onto the Si substrate with the SiO2 layer using a mask. The Au-SiO2 electrode was then treated in oxygen plasma at 100 W and 0.5 mbar for 20 seconds. The treated rigid substrate was then immersed in a (3-mercaptopropyl)trimethoxysilane (MPTS) / toluene solution (MPTS:toluene ≈ 1:19) for 6 hours, followed by washing with toluene and then ultrasonic cleaning in ethanol.

[0056] Now consider the ligand exchange (LE) process. The compact ligand NH4SCN is dispersed in methanol to form a 1 mg / ml solution. Once the EHDP process is complete, 80 μL of the NH4SCN solution is sprayed onto the printed pattern. After 1 minute, residual ligands, including SCN and oleic acid ligands, are washed away with methanol. The LE processes for TBAI and EDT are similar to those for NH4SCN. Specifically, a 99.99% TBAI solution is diluted with methanol to a concentration of 1 mg / ml, and a 99.99% EDT solution is diluted with acetonitrile (ACN) to a concentration of 0.005%.

[0057] To demonstrate the influence of the original Ag NC particle size and ligand number on the LE process of Ag NC particle fusion and growth, the LE process of Ag NC particles with different original diameters and various diffusion coefficients was simulated using the COMSOL PDE module, based on the number of surface ligands.

[0058] The LE process of AgNC is similar to that of sintering, and its conservative variable density ρ is governed by the Cahn-Hilliard equation:

[0059]

[0060] The non-transformation variable grain boundaries of particle η are governed by the Alan-Cahn equation:

[0061]

[0062] The free energy of a system is described by the free energy function:

[0063]

[0064] Where f(ρ,η) 1...p ) is the chemical free energy function, approximated by a Landau-type polynomial potential:

[0065]

[0066] The diffusion coefficient, which is related to the Ag NC structure and the number of ligands on the particle surface, is given by the following equation:

[0067]

[0068] Interpolation function Described by the following formula:

[0069]

[0070] This makes D vol It is zero in the pores and maximum in the solid region.

[0071] Conductivity testing was performed as follows. Ag NC lines and pads were printed between two adjacent Au electrodes using MPTS coating. Conductivity was tested after LE post-processing.

[0072] The conductivity σ of Ag NC wire is calculated by the following formula:

[0073]

[0074] Where R is the resistance being tested, W is the width of a single printed line, and T... h n is the thickness of the printed line. effect This refers to the number of effective conductive lines. n is determined by analyzing SEM images to exclude discontinuous and broken lines. effect .

[0075] This invention provides a general method for assembling and chemically modifying non-nuclear (NC) structures via layer-by-layer printing. Compared to conventional inkjet printing and high-temperature post-sintering, the method of this invention utilizes nanometer-resolution EHDP and room-temperature LE processes to diversify NC ink properties, substrate compatibility, and the variety of printed microelectronic functions. It has been discovered that dynamic NC-ligand coordination during printing determines the thermodynamic driving force for the chemical fusion of NCs.

[0076] The semiconductor properties of printed PbS NC and assembled multilayer photodiode devices were verified. Asymmetric metal electrodes enhanced diode performance, and fabrication via printing different metal NCs is simpler and more flexible than metallization after repeated photolithography processes. This versatile approach provides a practical solution to the key challenges of integrating heterogeneous materials and devices on both rigid and flexible substrates.

[0077] The above are merely specific embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Any modifications or substitutions that are obvious to those skilled in the art should fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be subject to the scope of the claims. References

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[0106] Although the invention has been explained with reference to certain embodiments, it should be understood that various modifications will become apparent to those skilled in the art upon reading the specification. Therefore, it should be understood that the invention disclosed herein is intended to cover such modifications falling within the scope of the appended claims.

Claims

1. A method for assembling nanocrystal (NC) submicron structures, characterized in that, Includes the following steps: The NC core material prepared with ligands is dispersed in a nonpolar solvent to form an ink; The ink is printed using inkjet printing technology, wherein the ink is ejected from a curved surface at the tip of a nozzle; As the ink is sprayed onto the substrate located on the movable platform, the nozzle is moved, or the movable platform is moved, to deposit NC in a line structure; and Control the movement of the nozzle or platform to create on-demand patterns and films with arbitrary shapes.

2. The method according to claim 1, characterized in that, The printing of the ink is performed via electrohydrodynamic printing (EHDP), which supports a variety of ink materials and ultra-high printing resolution beyond the diameter limitations of the nozzle's curved surface.

3. The method according to claim 2, characterized in that, The first layer of NC submicron structure was assembled using EHDP, followed by in-situ room-temperature chemical modification and functionalization of the layer; and Another NC layer is deposited on top of the first NC submicron structure, and then the other layer is chemically modified and functionalized in-situ at room temperature to achieve layer-by-layer 3D printing of NC microelectronic devices.

4. The method according to claim 2, characterized in that, The NC core material is one of metals, semiconductors, and metal oxides.

5. The method according to claim 4, characterized in that, The NC is Ag NC, Au NC, PbS NC, CdSe NC, ZnO NC or InSb NC in combination with a series of ligand reagents; the ligand reagent is EDT, NH4SCN or TBAI compact ligand reagent.

6. The method according to claim 5, characterized in that, When the ink is Ag NC ink with a concentration of 1.3 mg / ml and the nozzle outer diameter is 2 μm, the EHDP has an optimal pulse voltage of 300 V and a platform speed of 5 μm / s for printing nanowires.

7. The method according to claim 6, characterized in that, The ligand exchange (LE) parameters include immersion in a 1 mg / mL NH4SCN solution at room temperature for 60 seconds to provide a minimum linewidth of 70 nm for Ag NC printed on Si substrates.

8. The method according to claim 7, characterized in that, LE-assisted printing of continuous Ag NC lines forms 90×90μm 2 Or 50×50μm 2 The fourth fractal Hilbert curve or 200×200μm 2 Or 150×150μm 2 Other fractal orders, wherein the pattern is printed in one go, has a uniform linewidth of 400 nm and a thickness of less than 100 nm on straight paths and 90° turns.

9. The method according to claim 1, characterized in that, A gapless array of lines is printed to form a dense film by moving the platform forward and backward while maintaining a certain distance between two parallel lines. The printed NC lines are non-conductive and have a finite dielectric constant, which disturbs the surrounding electric field distribution and thus hinders the further printing of subsequent lines.

10. The method according to claim 1, characterized in that, The ligand is an oleic acid (OA) or oleylamine (OLAM) surface ligand.

11. The method according to claim 1, characterized in that, The NC core material is one of metals, semiconductors, and metal oxides.

12. The method according to claim 2, characterized in that, Further, chemical sintering and grain growth of NC are performed to achieve high conductivity in spin-coated Ag NC films, wherein when chemical treatment is applied to nanoprinted NC structures, LE-induced grain size evolution is more sensitive to the ink concentration used in the EHDP process.

13. The method according to claim 12, characterized in that, The chemical sintering process is influenced by the specific surface area (SSA, surface area / volume) of the Ag atom diffusion coefficient and the available free energy released during the LE process.

14. The method according to claim 1, characterized in that, The NC is formed by the following steps: Ag NC particles are combined with dodecane to achieve an ink concentration of 1 mg / ml to 8 mg / ml; and The Ag NC ink was ultrasonically treated at 25°C for 5 minutes.

15. A diffraction grating structure, characterized in that, It is formed using Ag NC lines with nanoscale resolution and high conductivity, formed by the method for assembling nanocrystal (NC) submicron structures according to claim 1, wherein the color gamut is attributable to narrow linewidth and adjustable line spacing as well as high printing speed.

16. An Ag NC electrode array, characterized in that, It is formed using Ag NC lines with submicron feature sizes suitable for single-cell monitoring and biosensing applications, through the method for assembling NC submicron structures according to claim 1.

17. An IR photodetector (PD), characterized in that, It is formed by using the method for assembling NC submicron structures according to claim 1, which forms micron-scale PbS NC patterns by using IR absorption of PbS NC.

18. A multilayer PbS NC photoconductor, characterized in that, It is formed by stacking a PbS NC film with an absorption peak of 950 nm on top of a PbS NC film with an absorption peak of 1500 nm using the method for assembling NC submicron structures according to claim 1. as well as Two printed NC films were processed using TBAI.

19. A fully printed PbS NC IR photodiode, characterized in that, It is formed by the method for assembling NC submicron structures according to claim 1 through the following steps: Ag and Au films were printed to form a bottom electrode pair, both assisted by NH4SCN LE; Printing a TBAI-treated PbS NC layer on an Ag electrode; The layer is covered with an EDT-treated PbS NC layer, which is printed to be connected to an Au electrode, wherein the overlapping region of the two PbS NC layers defines a pn junction; as well as The final device was formed by printing PbS NC with an absorption peak at around 1500 nm.

20. A fully printed PbS NC / ZnO NC IR photodiode, characterized in that, It contains Au NC-SCN / PbS NC-EDT / PbS NC-TBAI / ZnONC-SCN / Ag NC-SCN layers printed sequentially using the method for assembling NC submicron structures as described in claim 1.

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