Metal-mesh based transparent electrode on a 3-D curved surface by electrohydrodynamic jet printing

In the dc voltage-applied electrohydrodynamic (EHD) jet printing of metal nanoparticles, the residual charge of droplets deposited on a substrate changes the electrostatic field distribution and interrupts the subsequent printing behaviour, especially for insulating substrates that have slow charge decay rates. In this paper, a sinusoidal ac voltage was used in the EHD jet printing process to switch the charge polarity of droplets containing Ag nanoparticles, thereby neutralizing the charge on a polyethylene terephthalate (PET) substrate. Printed Ag lines with a width of 10 µm were invisible to the naked eye. After sintering lines with 500 µm of line pitch at 180 °C, a grid-type transparent electrode (TE) with a sheet resistance of ∼7 Ω sq−1 and a dc to optical conductivity ratio of ∼300 at ∼84.2% optical transmittance was obtained, values that were superior to previously reported results. In order to evaluate the durability of the TE under bending stresses, the sheet resistance was measured as the number of bending cycles was increased. The sheet resistance of the Ag grid electrode increased only slightly, by less than 20% from its original value, even after 500 cycles. To the best of our knowledge, this is the first time that Ag (invisible) grid TEs have been fabricated on PET substrates by ac voltage applied EHD jet printing.

Here, we suggest simple method for multi value slope In‐Ga‐Zn O (IGZO) thin‐film transistors (TFTs) using electrohydrodynamic (EHD) jet printing. To induce multi value slope, parasitic channel was intentionally formed on top of IGZO main channel using EHD jet printing. By precisely controlling parasitic channel regime with EHD jet printing, multi value slope could be realized without degradation in electrical performance of original IGZO TFTs.

This paper presents a non-contact printing mechanism for high aspect ratio silver (Ag) electrodes fabricated by an electrohydrodynamic (EHD) jet printing technique. Using high viscosity Ag paste ink, we were able to fabricate narrow and high aspect ratio electrodes. We investigated the effect of the surface energy of the substrate and improved the aspect ratio of printed lines through multiple printing. We fabricated the polycrystalline silicone solar cell with the Ag electrode and achieved cell efficiency of around 13.7%. The EHD jet printing mechanism may be an alternative method for non-contact fabrication of solar cells electrodes.

Digital printing technologies—including inkjet printing, aerosol jet printing, and electrohydrodynamic jet printing—have emerged as promising strategies for next-generation electronic devices. However, the weak adhesion between printed electrodes and substrates can lead to electrode delamination, thereby compromising device reliability and lifetime. In this study, a dielectric interlayer was introduced to improve the adhesion of silver (Ag) mesh electrodes on glass, polyethersulfone film, and polyimide film substrates. The optimized electrode on PES film achieved an optical transmittance of 83% at 550 nm and line resistance of 0.3 Ω, confirming its suitability as a transparent electrode. The incorporation of the interlayer also enhanced the adhesion and mechanical flexibility across all substrates. Moreover, the printed electrodes exhibited uniform surface heating under an applied bias (≤DC 3 V), and their feasibility as low-power flexible transparent heaters was experimentally demonstrated. These findings present a simple and effective printing strategy for fabricating robust and multifunctional electrodes, offering enormous potential for the realization of future flexible and transparent electronic systems.

Electromechanical reliability of a flexible metal-grid transparent electrode prepared by electrohydrodynamic (EHD) jet printing

High-resolution additive direct writing of metal micro/nanostructures by electrohydrodynamic jet printing

This paper reports the use of advanced forms of electrohydrodynamic jet (e-jet) printing for creating micro- and nanoscale patterns of proteins on various surfaces ranging from flat silica substrates to structured plasmonic crystals, suitable for micro/nanoarray analysis and other applications in both fluorescent and plasmonic detection modes. The approaches function well with diverse classes of proteins, including streptavidin, IgG, fibrinogen, and γ-globulin. Detailed study reveals that the printing process does not adversely alter the protein structure or function, as demonstrated in the specific case of streptavidin through measurements of its binding specificity to biotin-modified DNA. Multinozzle printing systems enable several types of proteins (up to four currently) to be patterned on a single substrate, in rapid fashion and with excellent control over spatial dimensions and registration. High-speed, pulsed operational modes allow large-area printing, with narrow statistical distributions of drop size and spacing in patterns that include millions of droplets. The process is also compatible with the structured surfaces of plasmonic crystal substrates to enable detection without fluorescence. These collective characteristics suggest potential utility of e-jet techniques in wide-ranging areas of biotechnology, where its compatibility with various biomaterials and substrates with different topographies and surface chemistries, and ability to form deposits that range from thick films to submonolayer coatings, derive from the remote, noncontacting physical material transfer mode of operation.

This paper discusses a run-to-run iterative learning control (ILC) algorithm for Electrohydrodynamic jet (E-jet) printing. E-jet printing is a nano-manufacturing process that uses electric field induced fluid jet printing through nano-scale nozzles for achieving better control and resolution than traditional jet-printing processes. The printing process is controlled by changing the voltage potential between the nozzle and the substrate. However, it is difficult to maintain constant operating conditions such as stand-off height during a run of the printing process. The change in operating conditions results in fluctuating jet frequency. For stabilizing the jetting frequency across a single run, we propose a proportional ILC algorithm. We determine the jetting frequency by recording the electric current pulses when ink droplets are released from the nozzle. The frequency profile obtained from current measurements is then used to shape the voltage profile across a run to compensate for changing operating conditions. Experimental results are presented to validate the proposed control method.

The macroscopic assembly of two-dimensional materials into a laminar structure has received considerable attention because it improves both the mechanical and chemical properties of the original materials. However, conventional manufacturing methods have certain limitations in that they require a high temperature process, use toxic solvents, and are considerably time consuming. Here, we present a new system for the self-assembly of layer-by-layer (LBL) graphene oxide (GO) via an electrohydrodynamic (EHD) jet printing technique. During printing, the orientation of GO flakes can be controlled by the velocity distribution of liquid jet and electric field-induced alignment spontaneously. Closely-packed GO patterns with an ordered laminar structure can be rapidly realized using an interfacial assembly process on the substrates. The surface roughness and electrical conductivity of the LBL structure were significantly improved compared with conventional dispensing methods. We further applied this technique to fabricate a reduced graphene oxide (r-GO)-based supercapacitor and a three-dimensional (3D) metallic grid hybrid ammonia sensor. We present the EHD-assisted assembly of laminar r-GO structures as a new platform for preparing high-performance energy storage devices and sensors.

Drop-on-demand printing is receiving a great deal of interest in industrial applications; however, the desired pattern sizes are realized by trial and error, through repeated printing experiments with varied materials (ink and suspended particles), operating conditions (voltage, flow rate, nozzle-to-plate distance, etc.), and substrate wettability. Since this approach requires a great deal of time, cost, and effort, a more convenient and efficient method that will predict pattern sizes with a minimal number of experiments is needed. In this study, we patterned a series of Ag dots and lines using a pulsed voltage-applied electrohydrodynamic jet printing system and measured their sizes with an optical microscope. We then applied a model suggested by Stringer and Derby (J Eur Ceram Soc 29:913–918, 2009) and Gao and Sonin (Proc R Soc Lond Ser A 444:533–554, 1994) to predict the pattern sizes, comparing these predictions with the measured sizes. Finally, we demonstrated our methodology on disconnected line repairing.

Cone-jet printing of aligned silver nanowire/poly(ethylene oxide) composite electrodes for organic thin-film transistors

Sputtered transparent electrodes for optoelectronic devices: Induced damage and mitigation strategies

Bioelectronic interfaces and biohybrid technologies have emerged as powerful solutions for sensing and manipulation applications. A unique method of underwater chemical sensing via a combination of engineered microbes and bioelectronic interfaces is discussed here with the goal of reporting to autonomous robotics through an electronic nervous system. The fabrication of these interfaces warrants a deposition method capable of precisely implementing the electronic, interfacial, and biological layers necessary for reliable devices. Electrohydrodynamic jet (e-jet) printing has been shown capable of doing so at a biologically relevant scale of 240 ± 50 nm. An e-jet printing system was fabricated and modified to use additive manufacturing to fabricate heterogeneous interfaces for the biological reporters Nitric Oxide and luminescence. These tasks included the fabrication of electronics that typically have multiple materials and thus multiple layers in their architecture; a potential point of failure in this liquid phase deposition method. The implementation of code based ejection modalities and a heated vacuum chuck allow for controlled volume deposition and rapid solvent evaporation, alleviating dissolution events in the sublayer. By eliminating these events, controlling film thickness to deter pinhole formation, and generating inks with solvents that were incompatible with sublayers, multi-layer electrochemical nitric oxide sensors and photosensors were produced. The fabricated multi-layer nitric oxide sensor has a lower limit of detection range of 188.5 nM - 314.5 nM; levels at which RAW 264.7 macrophage depolarization can be monitored in real time. An alternative bioelectronic interface is being studied wherein a modified version of this sensor is interfaced with Shewanella oneidensis to detect aqueous toxins. The photosensor architecture is comprised of a transparent PET substrate, an ITO cathode (pre-deposited), a bulk heterojunction P3HT:PC₇₁BM active layer, and a silver anode, with a final maximum spectral response of 7 mA/W and 90 mA/W/mm² at 514 nm, with a broad visible light spectrum from 400 nm to 620 nm. In interfacing these sensors with Vibrio fischeri, emitting light at 490 nm, the concentration of auto inducers in solution has been monitored in real time. These studies have created a clear path toward the fruition of olfactory guided, underwater autonomous robotics.

This article focuses biosensors based on the electrohydrodynamic jet printing processes, including the fabrication process, micro/nano‐material characteristics, and the sensing principle. Electrohydrodynamic jet printing provides a novel way to fabricate micro/nano‐structures for flexible/wearable biosensors with excellent characteristics of low detection limits, high sensitivities, and fast responses. The nonwoven nanofibrous mats have been used as support substrates, detection elements, and sensor electrodes to enhance the sampling, reaction, and detection in the biosensing processes. Large‐scale electrospinning techniques are discussed to efficiently produce nanofibers for the industrial nanofiber applications. The near‐field electrospinning technique is also introduced which can overcome the bending instability in the nanofiber deposition process to make orderly nanofibrous patterns as the sacrificial structure for the fabrication of microfluidic chips as bioreactor chambers. The functional nanofibers increase the biosensing interfaces and sensing sensitivity with good flexibility to realize applications such as the vital signs detection for the fields of disease diagnosing, infection control, and health care. With these great advantages, electrohydrodynamic jet printing provides new opportunities for the development of point of care medical.

Electrohydrodynamic (EHD) printing is a promising technique for additive manufacturing of high-resolution features with low cost and high efficiency. One of the major issues in EHD printing is nozzle clogging, which often occurs in the printing of colloidal inks with high concentrations. We proposed a new EHD printing nozzle configuration with dual channels to enable ink flow circulation to resolve the above issue. In this study, we focused on the meniscus dynamics and jetting characteristics of this new EHD printing process. Various jetting modes, i.e. continuous jet, pulsating jet, and pulsating droplet, as a function of the electric field intensity and nozzle configuration, were discussed. Dot patterns on a flexible substrate have been demonstrated via the new EHD printing process when operated at the pulsating droplet mode.