Inkjet Printing Technique Research Articles

Scalable Inkjet Printing of Electrochromic Smart Windows for Building Energy Modulation

Electrochromic smart windows are promising for green buildings due to energy efficiency, long optical memory effect, and tunable optical transmission. However, their wide application in buildings is impeded by challenges in scalability, cost‐effectiveness, and limited optical contrast. Quantitative field study of energy savings enabled by electrochromic smart windows in buildings is also lacking. Herein, with the established inkjet printing procedures, electrochromic smart windows (900 cm2) are fabricated. With large optical contrast (≈60%), fast switching kinetics (tc = 43 s, tb = 70 s), and long optical memory retention (transmittance <10% for 7 h), when installed onto the outdoor testbed, these electrochromic smart windows can effectively reduce the internal temperature, especially in summer tropical weather. The energy savings brought by electrochromic smart windows are found to be higher in sunny days than in rainy days. Specifically in a sunny day, the heat gain reduction can reach 42.3%, and for a comfortable targeted indoor temperature of 25 °C, the cooling load savings can be 28.9% compared to regular double‐glazing units‐based reference testbed. This study demonstrates the scalability of inkjet printing technique for fabricating large‐area electrochromic devices and the substantial energy savings obtained from testbed results.

Broadband Polarization-Insensitive Inkjet-Printed Conformal Metamaterial Absorber

The objective of this article is to devise a cost-effective, conformal, polarization-insensitive, and broadband metamaterial absorber for X-band applications. A periodic subwavelength conducting grid pattern is printed over flexible papers in a multi-layered fashion to achieve the broadband behavior. A silver nanoparticle incorporated inkjet printing technique is employed that does not require any post-processing such as sintering. The absorber is eco-friendly and suitable for rapid mass production at a low-cost. Moreover, the printed patterns do not crack when bent or applied over curved surfaces. The characteristics, working principle, and equivalent circuit of the absorber are described. The absorber is designed on a 1.06 mm (0.03 $\mathbf {{\lambda} _{\it l}}$ at the lowest working frequency) ultrathin substrate. It exhibits more than 90% absorptivity from 8.43 to 10.38 GHz for all angles of polarization with wide angular stability up to 45 $\text{\boldmath $^\circ $}$ . The flexibility and broadband feature is also confirmed by the experimental measurement of the fabricated prototype.

Inkjet-printed low-dimensional materials-based complementary electronic circuits on paper

Complementary electronics has represented the corner stone of the digital era, and silicon technology has enabled this accomplishment. At the dawn of the flexible and wearable electronics age, the seek for new materials enabling the integration of complementary metal-oxide semiconductor (CMOS) technology on flexible substrates, finds in low-dimensional materials (either 1D or 2D) extraordinary candidates. Here, we show that the main building blocks for digital electronics can be obtained by exploiting 2D materials like molybdenum disulfide, hexagonal boron nitride and 1D materials such as carbon nanotubes through the inkjet-printing technique. In particular, we show that the proposed approach enables the fabrication of logic gates and a basic sequential network on a flexible substrate such as paper, with a performance already comparable with mainstream organic technology.

Influence of Ink Curing in UV LED Inkjet Printing on Colour Differences, Ink Bleeding and Abrasion Resistance of Prints on Textile

Digital printing techniques are increasingly present in the field of textile printing. Particularly prominent is the inkjet printing technique using water-based inks, UV LED inkjet printing also increasingly being in use. UV LED inkjet is primarily not intended for direct clothing printing; however, it can be used especially as a hybrid solution in the soft signage market. It is a great option for the printers that are not engaged only in textile printing, and want a more versatile print portfolio, extending it to non-clothing textile products, e.g. soft signage and non-wearable products. As these types of products often require colour reproduction of logos, accurate colour reproduction, good ink adhesion and sharpness are important just like in other printing technologies. In order to evaluate the impact of UV LED radiation amount on colour differences, ink bleeding and abrasion resistance, six different fabric samples (five woven and one nonwoven) were printed using a UV LED inkjet printer. Based on the results of colour difference, it was established that a reduction of UV radiation (by half the manufacturer’s recommended amount) had no effect on this parameter. However, perceptible colour differences were observed with the use of different M measurement conditions defined by the international standard ISO 13655-2017. Reducing the amount of UV radiation had no effect on the adhesion and durability of the printed ink. Small differences detected in these two parameters were mainly a consequence of the properties of textile materials and not of decreased UV radiation.

Inkjet printed polyelectrolyte multilayer membrane using a polyketone support for organic solvent nanofiltration

This study investigates the inkjet printing technique as an efficient way to fabricate polyelectrolyte multilayer membranes (PEM) for organic solvent nanofiltrtaion (OSN). Polyethyleneimine (PEI) and poly(sodium 4-styrene sulfonate) (PSS) were used as polycation and polyanion, respectively. Single walled carbon nanotube (SWCNT) was incorporated into membranes to enhance the membrane physical and chemical stability. The polyketone (PK) membrane served as substrate for OSN because of its organic solvent resistance property in nature. The effects of numbers of bilayer, polyelectrolyte concentration, and the cross-linking condition on the membrane OSN performances were evaluated. The best OSN performance was achieved with 10 bilayers of polyelectrolytes printing, noted as (PEI/PSS-CNT)10. The (PEI/PSS-CNT)10 membrane exhibited ethanol, methanol, IPA and acetone permeances of 2.52, 4.21, 1.21 and 4.75 L m−2 h−1 bar−1, respectively, along with good dye rejection rate (Rose Bengal (RB) rejection >98%). Moreover, the inkjet printed OSN membrane was found to be stable after soaking in different organic solvents for two weeks. The membrane weights and the performances exhibited negligible changes. The 12 h continuous filtration tests also confirmed the membrane stability property. Our work broadened the use of inkjet printing technology for membrane fabrication and validated the technology as a promising method for producing multilayer OSN membranes, which may open a new avenue for OSN membrane preparations.

Quantum Dot Self-Assembly Deposition in Physically Confined Microscale Space by Using an Inkjet Printing Technique.

Inkjet printing technique is susceptible to form coffer-ring patterns and inhomogeneous films owing to the evaporation and its accompanying hydrodynamics of microscale quantum dot droplet. Pioneer efforts are usually confined to two-dimensional flat substrates and inks with mixed solvents/additives. Herein we demonstrate that physically confined space offers an additional parameter in tailoring such processes of droplets and the following quantum-dot self-assembly deposition, without extra modification of quantum dots or solvent chemistry. Owing to the boundary of physically confined space, two three-phase border lines in both the bottom center (horizontal direction) and the barrier of the bank substrate (vertical direction) arise, inducing dual capillary flows and Marangoni backflows. The evaporation, fluid flow, and film-forming process in physically confined space are studied by introducing well-prepared single-solvent quantum dots inks. The systematical analysis offers valuable instructions including ink preparation, surface modification, and postprocessing evaporation technique for inkjet-printed patterning applications, especially for pixelated display, polychrome patterning, and sensor array.

Impact of inkjet printing parameters on the morphology and device performance of organic photovoltaics

The morphology of the active layer is vital for the device performance of organic electronics. However, most research is primarily focused on the active layer prepared from the spin coating method, which is not suitable for large area manufacturing. The inkjet printing technique has been widely studied in the field of organic electronics due to its advantages of scalability, patternability, and affordability. Nevertheless, morphological changes in the active layer during inkjet printing have received little attention. Herein, for the first time, the influence of inkjet printing parameters on the bulk heterojunction morphology and device performance of organic photovoltaics (OPVs) was systematically studied. The crystal sizes decreased as the inkjet printing speed or substrate temperature increased, which was vital for bimolecular recombination and carrier transport. Moreover, the π–π stacking distance decreased as the inkjet printing speed increased, which is beneficial to charge transport, resulting in improved device performance. However, an uneven film was formed when the substrate temperature increased, degrading the device performance. It is demonstrated that the control of inkjet printing parameters can effectively improve the morphology of active layer, paving guides for high-efficiency large-area production of OPVs and other organic electronics.

Inkjet-Printed Full-Color Matrix Quasi-Two-Dimensional Perovskite Light-Emitting Diodes.

Full-color matrix devices based on perovskite light-emitting diodes (PeLEDs) formed via inkjet printing are increasingly attractive due to their tunable emission, high color purity, and low cost. A key challenge for realizing PeLED matrix devices is achieving high-quality perovskite films with a favorable emission structure via inkjet printing techniques. In this work, a narrow phase distribution, high-quality quasi-two-dimensional (quasi-2D) perovskite film without a "coffee ring" was obtained via the introduction of a phenylbutylammonium cation into the perovskite and the use of a vacuum-assisted quick-drying process. Relatively efficient emissions of red, green, and blue (RGB) uniform quasi-2D perovskite films with high photoluminescence quantum yields were cast by the inkjet printing technique. The RGB monochrome perovskite matrix devices with 120 pixel-per-inch resolution exhibited electroluminescence, with maximum external quantum efficiencies of 3.5, 3.4, and 1.0% (for red, green, and blue light emissions, respectively). Furthermore, a full-color perovskite matrix device with a color gamut of 102% (NTSC 1931) was realized. To the best of our knowledge, this is the first report of a full-color perovskite matrix device formed by inkjet printing.

Metal Cation-Responsive and Excitation-Dependent Nontraditional Multicolor Fluorescent Hydrogels for Multidimensional Information Encryption.

Fluorescent polymeric hydrogels especially multicolor fluorescent polymeric hydrogels (MFPHs) have important applications in information storage, encryption, and encoding. MFPHs are generally prepared by incorporating multiple traditional fluorescent materials into hydrogels. In recent years, nontraditional luminescent polymers without any traditional π-conjugated chromophores have received increasing attention. Here, we report a novel type of nontraditional MFPHs prepared by in situ polymerization of acrylamide (AAm) in the presence of poly(itaconic acid) (PITAc). The hydrogen-bonded mechanically strong PAAm/PITAc hydrogels show strong intrinsic fluorescence, and the fluorescence emission is excitation-dependent and metal cation-responsive. More impressively, the hydrogels treated with metal cations also possess excitation-dependent fluorescence. We developed a multi-ion inkjet printing (MIIP) technique to print texts or designed patterns onto the hydrogel surface using different metal cation solutions as inks, and then variable texts or patterns appear under the irradiation of UV, violet, and blue lights. Patterns can be further changed by selective printing, erasing, or reprinting on some regions. Therefore, multidimensional information encryption is achieved. This work provides a new strategy for preparing MFPHs for wide applications.

Designing a nanocrystal-based temperature and strain multi-sensor with one-step inkjet printing

Wearable multi-sensors based on nanocrystals have attracted significant attention, and studies on patterning technology to implement such multi-sensors are underway. Conventional patterning processes may affect material properties based on high temperatures and harsh chemical conditions. In this study, we developed an inkjet printing technique that can overcome these drawbacks through the application of patterning processes at room temperature and atmospheric pressure. Nanocrystal-based ink is used to adjust properties efficiently. Additionally, the viscosity and surface tension of the solvents are investigated and optimized to increase patterning performance. In the patterning process, the electrical, electrothermal, and electromechanical properties of the nanocrystal pattern are controlled by the ligand exchange process. Experimental results demonstrate that a multi-sensor with a temperature coefficient of resistance of 3.82 × 10-3 K-1 and gauge factor of 30.6 can be successfully fabricated using one-step inkjet printing.

Inkjet Printing of Few‐Layer Enriched Black Phosphorus Nanosheets for Electronic Devices

AbstractBlack phosphorus (BP) is considered among the promising material for electronic devices. A wide range of studies involving properties, exfoliation, and applications of thin‐layered BP nanosheets (NSs) has been put forward. Along with understanding properties of thin‐layered BP NSs, efforts to enlighten the intrinsic characteristics of the BP film should be also accompanied to extend applications of the material. In this study, a facile and efficient inkjet printing approach is introduced to fabricate patterned BP films. This approach successfully addresses the complexity of the ink formulation and thus enables to pattern the high‐quality BP film at as high a resolution as tens of micrometers. The printed BP pattern provides its intrinsic characteristics including electronic properties, conducting mechanism, and stability, which are essential to advancing the printed BP electronic device. By integrating the printed BP pattern into a diode device, its potential for electronic devices is demonstrated. This inkjet printing technique will facilitate the development of printing patterns of 2D materials in a facile and cost‐effective manner and further boost the research on advanced electronic devices.

An inkjet-printed smartphone-supported electrochemical biosensor system for reagentless point-of-care analyte detection

In this work, we developed an inkjet-printed electrochemical enzyme-based biosensor system which can work with the smartphone for the point-of-care analyte detection. Inkjet printing technique was applied to functionalize electrodes. Multi-walled carbon nanotubes were used as the enzyme carrier to enhance the enzyme loading. Enzyme immobilization was realized through layer-by-layer printing strategy by crosslinking ink components (BSA and glutaraldehyde) between printing layers. Reagents for the enzyme catalyzed reaction were preloaded onto the working electrode to eliminate the use of traditional electrochemical cell. In addition, a versatile smartphone Android application was developed for real-time data processing on multiple occasions. Phosphate in the artificial saliva was measured to demonstrate the feasibility of the proposed biosensor system. The miniaturized biosensor system presents a wide linear range with rapid response time (less than 10 s). High selectivity and stability of the sensor demonstrate its practical use for saliva test. The proposed biosensor system can be applicable for various analyte detection by exchanging the sensing elements and reagents. And the biosensor system can be easily operated by users without specific training. In all, this study demonstrated a novel fabrication strategy of integrated biosensor system which has great potentiality for point-of-care applications. Our proposed sensor system demonstrates a reliable and reproducible biosensor fabrication route that has meaningful reference for similar point-of-care biosensor systems.

Inkjet Printing of Polypyrrole Electroconductive Layers Based on Direct Inks Freezing and Their Use in Textile Solid-State Supercapacitors.

In this work, we propose a novel method for the preparation of polypyrrole (PPy) layers on textile fabrics using a reactive inkjet printing technique with direct freezing of inks under varying temperature up to −16 °C. It was found that the surface resistance of PPy layers on polypropylene (PP) fabric, used as a standard support, linearly decreased from 6335 Ω/sq. to 792 Ω/sq. with the decrease of polymerization temperature from 23 °C to 0 °C. The lowest surface resistance (584 Ω/sq.) of PPy layer was obtained at −12 °C. The spectroscopic studies showed that the degree of the PPy oxidation as well as its conformation is practically independent of the polymerization temperature. Thus, observed tendences in electrical conductivity were assigned to change in PPy layer morphology, as it is significantly influenced by the reaction temperature: the lower the polymerization temperature the smoother the surface of PPy layer. The as-coated PPy layers on PP textile substrates were further assembled as the electrodes in symmetric all-solid-state supercapacitor devices to access their electrochemical performance. The electrochemical results demonstrate that the symmetric supercapacitor device made with the PPy prepared at −12 °C, showed the highest specific capacitance of 72.3 F/g at a current density of 0.6 A/g, and delivers an energy density of 6.12 Wh/kg with a corresponding power density of 139 W/kg.

Synthesis of fluorescence inks based on imino qumarines derivatives and their application in textile printing

Preparation of fluorescent three inkjet inks based on N-(4-bromophenyl)-2-(2-imino-2H-chromen-3-yl) benzo[d]thiazole-5-sulfonamide derivatives the structures of compounds are confirmed via, element analysis, IR, H-NMR, and Mass spectra , microencapsulation and surface modification methods are used to prepare the inks, then printed on polyester, polyamide and paper, by inkjet printing technique as a printed security features.

Fully inkjet-printed BaTiO3 capacitive humidity sensor: Microstructural engineering of the humidity sensing layer using bimodal ink

Humidity sensors are often used in industries where humidity levels must be monitored due to their possible effects on the manufacturing processes and products. These sensors must possess high sensitivity that can detect changes in the environment's humidity level. This paper presents a novel technique to improve the sensing performance of humidity sensors by varying the microstructure of the BaTiO3 humidity sensing layers by optimizing the mixing ratios of the bimodal inks deposited by the inkjet printing technique. By varying the mixing ratio of bimodal inks, the surface area, pore size, and packing density of the humidity sensing layers were modulated because of the incorporation of smaller particles into larger particles. The optimal sensor was produced by a 70:30 mixing ratio due to its higher surface area, which allowed a higher area for water adsorption and therefore improved the humidity sensitivity. Microstructural analyses, such as Focused-Ion-Beam Field-Emission Scanning Electron Microscope (FIB FE-SEM), image analysis, and Brunauer–Emmett–Teller (BET) were performed to examine the microstructural differences of the sensors. The fully inkjet-printed BaTiO3 capacitive sensors, which had the optimal mixing ratio, exhibited a high sensitivity of 5.75 × 105 pF/%RH, which exceeded that of most reported humidity sensors, good repeatability, a linearity of 0.989, an acceptable response and recovery time of 41 s and 34 s, respectively, low hysteresis, and good stability over a long period of time. The fabricated BaTiO3-based capacitive humidity sensor exhibited an outstanding performance that can be utilized toward various applications.

Metabolism-Based Capture and Analysis of Circulating Tumor Cells in an Open Space.

The level of circulating tumor cells (CTCs) in blood is a predictor of metastatic cancer progress, serving as an important biomarker for cancer diagnosis, prognosis, and therapy. Currently, there are mainly two conventional strategies to distinguish CTCs, including biological property-based affinity capture and physical property-based label-free isolation. Although great progress has been made in this field, the ability to distinguish CTCs still needs to be improved further due to the cell heterogeneity. Herein, a metabolism-based isolation approach was applied to identify tumor cells according to the "Warburg effect", and a bifunctional open-space platform with fluid walls was developed for real-time monitoring and in situ capture/analysis of tumor cells. A drop-on-demand inkjet printing technique was introduced to create a single cell-containing droplet array with high throughput and high encapsulation rate, and the homogeneous crystalline matrix spots ejected from the inkjet also provided high-quality and reproducible lipid profiling. This platform could combine both microscopic image and mass data, and it has been proven to be capable of isolating and identifying CTCs in complex blood samples, making it a promising tool for evaluating the efficacy of therapy and monitoring the disease progression.

High-brightness perovskite quantum dot light-emitting devices using inkjet printing

Abstract The performance of perovskite quantum dot light-emitting diodes (PeQLEDs) has been rapidly enhanced recently, but the devices are still stuck in the stage of using small-scale solution processes, such as spin-coating. In this work, we report the realization of high performance PeQLEDs by using inkjet printing technique. We demonstrate the preparation of a printable perovskite quantum dot ink by using a hybrid solvent consisting of high boiling solvent dodecane and low boiling solvent n-octane. A universal strategy for eliminating coffee rings during inkjet printing of perovskite inks is developed based on the modulation of ink formulation, and the stacking model of perovskite quantum dot in a pixel pit structure is proposed. The inkjet-printed PeLEDs exhibit a low turn-on voltage of 2.7 V, a brightness of 10992 cd/m2 at 6.6 V and a maximum current efficiency of 8.67 cd/A, which is by far the highest value reported for inkjet-printed PeLEDs. The results pave a way for future realization of high performance pixelated PeLED displays with inkjet printing technique.

Fabrication of circuits by multi-nozzle electrohydrodynamic inkjet printing for soft wearable electronics

Wearable electronic devices are evolving from current rigid configurations to flexible and ultimately stretchable structures. These emerging systems require soft circuits for connecting the various working units of the overall system. This paper presents fabrication of soft circuits by electrohydrodynamic (EHD) inkjet-printing technique. Multi-nozzle EHD printing head is employed for rapid fabrication of electric circuits on a wide set of materials, including glass substrate (rigid), flexible polyethylene terephthalate (PET) films, and stretchable thermoplastic polyurethane (TPU) films. To avoid the effects of substrate materials on the jettability, the proposed multi-nozzle head is equipped with integrated individual counter electrodes (electrodes are placed above the printing substrate). High-resolution circuits (50 ± 5 µm) with high electrical conductivity (0.6 Ω □−1) on soft substrate materials validate our well-controlled multi-nozzle EHD printing approach. The produced circuits showed excellent flexibility (bending radius ≈ 5 mm radius), high stretchability (strain ≈ 100%), and long-term mechanical stability (500 cycles at 30% strain). The concept is further demonstrated with a soft strain sensor based on a multi-nozzle EHD-printed circuit, employed for monitoring the human motion (finger bending), indicating the potential applications of these circuits in soft wearable electronic devices.Graphic

Printing Methods in the Production of Orodispersible Films.

Orodispersible film (ODF) formulations are promising and progressive drug delivery systems that are widely accepted by subjects across all the age groups. They are traditionally fabricated using the most popular yet conventional method called solvent casting method. The most modern and evolving method is based on printing technologies and such printed products are generally termed as printed orodispersible films (POFs). This modern technology is well suited to fabricate ODFs across different settings (laboratory or industrial) in general and in a pharmacy setting in particular. The present review provides an overview of various printing methods employed in fabricating POFs. Particularly, it provides insight about preparing POFs using inkjet, flexographic, and three-dimensional printing (3DP) or additive manufacturing techniques like filament deposition modeling, hot-melt ram extrusion 3DP, and semisolid extrusion 3DP methods. Additionally, the review is focused on patenting trends in POFs using ESPACENET, a European Patent Office search database. Finally, the review captures future market potential of 3DP in general and ODFs market potential in particular.

Inkjet-Printed Quantum Dot Fluorescent Security Labels with Triple-Level Optical Encryption.

Optical security labels play a significant role in protecting both our wealth and health. However, simultaneously meeting the requirements including low-cost fabrication, easy detection, and high-level security is still challenging for security labels. Here, we design an unclonable anti-counterfeiting system with triple-level security by using the inkjet printing technique, which can be authenticated by naked eyes, a portable microscope, and a fluorescence microscope. These labels are achieved by printing microscale quantum dot (QD) ink droplets on premodified substrates with random-distributed glass microspheres. Due to the unique capillary action induced by the glass microspheres, QDs in the ink droplets are deposited around the microspheres, forming microscale multicircular patterns. Multiple pinning of QDs at the three-phase contact lines appears during the evaporation of the droplet, resulting in the formation of a nanoscale labyrinthine pattern around the microspheres. The nanoscale labyrinth pattern and the microscale multicircular microsphere array, together with the printed macroscopic image, constitute a triple-level progressive anti-counterfeiting system. Moreover, the system is compatible with an artificial intelligence-based identification strategy that allows rapid identification and verification of the unclonable security labels.