Droplet morphology analysis of drop-on-demand inkjet printing

As an accurate 2D/3D fabrication tool,inkjet printing technology has great potential in preparation of micro electronic devices.The morphology of droplets produced by the inkjet printer has a great impact on the accuracy of deposition.In this study,the drop-on-demand(DoD)inkjet simulation model was established,and the accuracy of the simulation model was verified by corresponding experiments.The simulation result shows that the velocity of the droplet front and tail,as well as the time to disconnect from the nozzle is mainly affected by density(ρ),viscosity(μ)and surface tension(σ)of droplets.When the liquid filament is about to disconnect from the nozzle,the filament length and filament front velocity are found to have a linear correlation withσ/ρμand ln(ρ/(μσ1/2)).

Carbon-Based Flexible and All-Solid-State Micro-supercapacitors Fabricated by Inkjet Printing with Enhanced Performance

By means of inkjet printing technique, flexible and all-solid-state micro-supercapacitors(MSCs) were fabricated with carbon-based hybrid ink composed of graphene oxide(GO,98.0vol.%) ink and commercial pen ink(2.0vol.%). A small amount of commercial pen ink was added to effectively reduce the agglomeration of theGO sheets during solvent evaporation and the following reduction processes in which the presence of graphite carbon nanoparticles served as nano-spacer to separate GO sheets. The printed device fabricated using the hybrid ink,combined with the binder-free microelectrodes and interdigital microelectrode configuration, exhibits nearly 780%enhancement in areal capacitance compared with that of pure GO ink. It also shows excellent flexibility and cycling stability with nearly 100% retention of the areal capacitance after 10,000 cycles. The all-solid-state device can be optionally connected in series or in parallel to meet the voltage and capacity requirements for a given application.This work demonstrates a promising future of the carbonbased hybrid ink for directly large-scale inkjet printing MSCs for disposable energy storage devices.

An overview on the principle of inkjet printing technique and its application in micro-display for augmented/virtual realities

Augmented reality(AR)and virtual reality(VR)are two novel display technologies that are under updates.The essential feature of AR/VR is the full-color display that requires high pixel densities.To generate three-color pixels,the fluorescent color conversion layer inevitably includes green and red pixels.To fabricate such sort of display kits,inkjet printing is a promising way to position the color conversion layers.In this review article,the progress of AR/VR technologies is first reviewed,and in succession,the state of the art of inkjet printing,as well as two key issues-the optimization of ink and the reduction of coffee-ring effects,are introduced.Finally,some potential problems associated with the color converting layer are highlighted.

Drying-Mediated Self-Assembly of Graphene for Inkjet Printing of High-Rate Micro-supercapacitors

Scalable fabrication of high-rate micro-supercapacitors(MSCs)is highly desired for on-chip integration of energy storage components.By virtue of the special self-assembly behavior of 2D materials during drying thin films of their liquid dispersion,a new inkjet printing technique of passivated graphene micro-flakes is developed to directly print MSCs with 3D networked porous microstructure.The presence of macroscale through-thickness pores provides fast ion transport pathways and improves the rate capability of the devices even with solid-state electrolytes.During multiple-pass printing,the porous microstructure effectively absorbs the successively printed inks,allowing full printing of 3D structured MSCs comprising multiple vertically stacked cycles of current collectors,electrodes,and sold-state electrolytes.The all-solid-state heterogeneous 3D MSCs exhibit excellent vertical scalability and high areal energy density and power density,evidently outperforming the MSCs fabricated through general printing techniques.

Additive manufacturing of thin electrolyte layers via inkjet printing of highly-stable ceramic inks

Inkjet printing is a promising alternative for the fabrication of thin film components for solid oxide fuel cells(SOFCs) due to its contactless, mask free, and controllable printing process. In order to obtain satisfying electrolyte thin layer structures in anode-supported SOFCs, the preparation of suitable electrolyte ceramic inks is a key. At present, such a kind of 8 mol% Y_(2)O_(3)-stabilized ZrO_(2)(8 YSZ) electrolyte ceramic ink with long-term stability and high solid loading(> 15 wt%) seems rare for precise inkjet printing, and a number of characterization and performance aspects of the inks, such as homogeneity, viscosity, and printability, should be studied. In this study, 8 YSZ ceramic inks of varied compositions were developed for inkjet printing of SOFC ceramic electrolyte layers. The dispersing effect of two types of dispersants, i.e., polyacrylic acid ammonium(PAANH4) and polyacrylic acid(PAA), were compared. The results show that ultrasonic dispersion treatment can help effectively disperse the ceramic particles in the inks. PAANH4 has a better dispersion effect for the inks developed in this study. The inks show excellent printable performance in the actual printing process. The stability of the ink can be maintained for a storage period of over 30 days with the help of initial ultrasonic dispersion. Finally, micron-size thin 8 YSZ electrolyte films were successfully fabricated through inkjet printing and sintering, based on the as-developed high solid loading 8 YSZ inks(20 wt%). The films show fully dense and intact structural morphology and smooth interfacial bonding, offering an improved structural quality of electrolyte for enhanced SOFC performance.

Effects of the actuation waveform on the drop size reduction in drop-on-demand inkjet printing

In this study the effects of the actuation waveforms on the droplet generation in a drop-on-demand inkjet printing are studied systematically by numerical simulations.Two different types of waveforms,namely the unipolar and bipolar actuations,are investigated for three fluids with different physical properties.We focus on two key parameters,which are the dwell time and the velocity amplitude.For the unipolar driving,the ejection velocity and the ejected liquid volume are both increased as the velocity amplitude becomes larger.The dwell time only has minor effects on both the ejection velocity and the ejected liquid volume.The ejection velocity decreases significantly for large liquid viscosity,while the influences of viscosity on the ejected liquid volume are much weaker.Four different droplet morphologies and the corresponding parameter ranges are identified.The droplet radius can be successfully reduced to about 40%e of the nozzle exit radius.For the bipolar waveforms,same droplet morphologies are observed but with shifted boundaries in the phase space.The minimal radius of stable droplet produced by the bipolar waveforms is even smaller compared to the unipolar ones.

Inkjet printing technology for increasing the I/O density of 3D TSV interposers

Interposers with through-silicon vias(TSVs)play a key role in the three-dimensional integration and packaging of integrated circuits and microelectromechanical systems.In the current practice of fabricating interposers,solder balls are placed next to the vias;however,this approach requires a large foot print for the input/output(I/O)connections.Therefore,in this study,we investigate the possibility of placing the solder balls directly on top of the vias,thereby enabling a smaller pitch between the solder balls and an increased density of the I/O connections.To reach this goal,inkjet printing(that is,piezo and super inkjet)was used to successfully fill and planarize hollow metal TSVs with a dielectric polymer.The under bump metallization(UBM)pads were also successfully printed with inkjet technology on top of the polymer-filled vias,using either Ag or Au inks.The reliability of the TSV interposers was investigated by a temperature cycling stress test(−40℃ to+125℃).The stress test showed no impact on DC resistance of the TSVs;however,shrinkage and delamination of the polymer was observed,along with some micro-cracks in the UBM pads.For proof of concept,SnAgCu-based solder balls were jetted on the UBM pads.

Zwitterion-assisted transition metal dichalcogenide nanosheets for scalable and biocompatible inkjet printing

Inkjet printing of two-dimensional(2D)transition metal dichalcogenide(TMD)nanosheets fabricated by liquid-phase exfoliation(LPE)allows simple,mass-producible,and low-cost photo-electronic devices.Many LPE processes involve toxic and environmentally hazardous solvents;however,dispersants have restricted the extent of applications of 2D-TMD inks.Herein,various 2D-TMD nanosheets,including MoS2,MoSe2,WS2,and WSe2,in addition to few-layered graphene,are inkjet-printed using a LPE process based on zwitterionic dispersants in water.Zwitterions with cationic and anionic species are water-soluble,while alkyl chain moieties associated with two ionic species adhere universally on the surface of TMD nanosheets,resulting in high throughput liquid exfoliation of the nanosheets.The zwitterion-assisted TMD nanosheets in water are successtully employed as an ink without the need for additives to adjust the viscosity and surface tension of the ink for use in an office inkjet printer;this gives rise to A4 scale,large-area inkjet-printed images on diverse substrates,such as metals,oxides,and polymer substrates patchable onto human skin.Combination with conductive graphene nanosheet inks allowed the development of mechanically flexible,biocompatible-printed arrays of photodetectors with pixelated MoSe2 channels on a paper exhibiting a photocurrent ON/OFF ratio of approximately 1038 and photocurrent switching of 500 ms.

Inkjet printing of epitaxially connected nanocrystal superlattices

Access to a blossoming library of colloidal nanomaterials provides building blocks for complex assembled materials.The journey to bring these prospects to fruition stands to benefit from the application of advanced processing methods.Epitaxially connected nanocrystal(or quantum dot)superlattices present a captivating model system for mesocrystals with intriguing emergent properties.The conventional processing approach to creating these materials involves assembling and attaching the constituent nanocrystals at the interface between two immiscible fluids.Processing small liquid volumes of the colloidal nanocrystal solution involves several complexities arising from the concurrent spreading,evaporation,assembly,and attachment.The ability of inkjet printers to deliver small(typically picoliter)liquid volumes with precise positioning is attractive to advance fundamental insights into the processing science,and thereby potentially enable new routes to incorporate the epitaxially connected superlattices into technology platforms.In this study,we identified the processing window of opportunity,including nanocrystal ink formulation and printing approach to enable delivery of colloidal nanocrystals from an inkjet nozzle onto the surface of a sessile droplet of the immiscible subphase.We demonstrate how inkjet printing can be scaled-down to enable the fabrication of epitaxially connected superlattices on patterned sub-millimeter droplets.We anticipate that insights from this work will spur on future advances to enable more mechanistic insights into the assembly processes and new avenues to create high-fidelity superlattices.

Efficient emission of quasi-two-dimensional perovskite films cast by inkjet printing for pixel-defined matrix light-emitting diodes

Quasi-two-dimensional(quasi-2D)perovskites are promising materials for potential application in light-emitting diodes(LEDs)due to their high exciton binding energy and efficient emission.However,their luminescent performance is limited by the low-n phases that act as quenching luminescence centers.Here,a novel strategy for eliminating low-n phases is proposed based on the doping of strontium bromide(SrBr_(2))in perovskites,in which SrBr_(2)is able to manipulate the growth of quasi-2D perovskites during their formation.It was reasonably inferred that SrBr_(2)readily dissociated strontium ions(Sr^(2+))in dimethyl sulfoxide solvent,and Sr^(2+)was preferentially adsorbed around[PbBr_(6)]^(4−)through strong electrostatic interaction between them,leading to a controllable growth of quasi-2D perovskites by appropriately increasing the formation energy of perovskites.It has been experimentally proved that the growth can almost completely eliminate low-n phases of quasi-2D perovskite films,which exhibited remarkably enhanced photoluminescence.A high electroluminescent efficiency matrix green quasi-2D perovskite-LED(PeLED)with a pixel density of 120 pixels per inch fabricated by inkjet printing technique was achieved,exhibiting a peak external quantum efficiency of 13.9%,which is the most efficient matrix green quasi-2D PeLED so far to our knowledge.

Efficient red perovskite quantum dot light-emitting diode fabricated by inkjet printing

Perovskite quantum dots(PeQDs)are considered potential display materials due to their high color purity,high photoluminescence quantum yield(PLQY),low cost and easy film casting.In this work,a novel electroluminescence(EL)device consisting of the interface layer of long alkyl-based oleylammonium bromide(OAmBr),which passivates the surface defects of PeQDs and adjusts the carrier transport properties,was designed.The PLQY of the OAmBr/PeQD bilayer was significantly improved.A high-performance EL device with the structure of indium tin oxide/poly(3,4-ethylenedioxythiophene)polystyrene sulfonate/poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine)/OAmBr/PeQDs/2,2′,2′′-(1,3,5-benzinetriyl)-tris(1-phenyl-1H benzimidazole)/LiF/Al was constructed using a spin-coating method.A peak external quantum efficiency(EQE)of 16.5%at the emission wavelength of 646 nm was obtained.Furthermore,an efficient matrix EL device was fabricated using an inkjet printing method.A high-quality PeQD matrix film was obtained by introducing small amounts of polybutene into the PeQDs to improve the printing process.The EQE reached 9.6%for the matrix device with 120 pixels per inch and the same device structure as that of the spin-coating one.

Programmable robotized‘transfer-and-jet’printing for large,3D curved electronics on complex surfaces

Large,3D curved electronics are a trend of the microelectronic industry due to their unique ability to conformally coexist with complex surfaces while retaining the electronic functions of 2D planar integrated circuit technologies.However,these curved electronics present great challenges to the fabrication processes.Here,we propose a reconfigurable,mask-free,conformal fabrication strategy with a robot-like system,called robotized‘transfer-and-jet’printing,to assemble diverse electronic devices on complex surfaces.This novel method is a ground-breaking advance with the unique capability to integrate rigid chips,flexible electronics,and conformal circuits on complex surfaces.Critically,each process,including transfer printing,inkjet printing,and plasma treating,are mask-free,digitalized,and programmable.The robotization techniques,including measurement,surface reconstruction and localization,and path programming,break through the fundamental constraints of 2D planar microfabrication in the context of geometric shape and size.The transfer printing begins with the laser lift-off of rigid chips or flexible electronics from donor substrates,which are then transferred onto a curved surface via a dexterous robotic palm.Then the robotic electrohydrodynamic printing directly writes submicrometer structures on the curved surface.Their permutation and combination allow versatile conformal microfabrication.Finally,robotized hybrid printing is utilized to successfully fabricate a conformal heater and antenna on a spherical surface and a flexible smart sensing skin on a winged model,where the curved circuit,flexible capacitive and piezoelectric sensor arrays,and rigid digital–analog conversion chips are assembled.Robotized hybrid printing is an innovative printing technology,enabling additive,noncontact and digital microfabrication for 3D curved electronics.

New Silica Coating Pigment for Inkjet Papers from Mining Industry Sidestreams

Silica is commonly used as an ingredient in the coatings of inkjet papers because of its capability to provide a coating layer structure combining a high pore volume, into which all the applied inkjet ink can transfer, and a suitable pore size distribution for very quick ink absorption. Nowadays, the production of silica pigment is quite expensive, and therefore, it would be advantageous to find a cheaper raw material source. In this study, the raw material was Greek olivine from magnesite mine sidestreams. The silica pigment was produced at laboratory scale by using nitric acid as a solvent. The target of this work was to clarify how this produced silica pigment is suited for inkjet coating pigments. The coating colors were applied by a laboratory rod coater on fine base paper and white-top kraftliner, and the coated surfaces were printed with a home and office area inkjet printer. The results showed that the produced olivine-based silica pigment has a potential in matt inkjet coatings. The coating of the produced silica pigment increased the print density, decreased the print-through, and diminished the bleeding of fine paper and white-top kraftliner board. However, further development work is needed to improve the pigment brightness to a more acceptable level, and to control the particle size at the nitric acid dissolution.

Inkjet printed large-area flexible circuits:a simple methodology for optimizing the printing quality

In this work, a simple methodology was developed to enhance the patterning resolution of inkjet printing, involving process optimization as well as substrate modification and treatment. The line width of the inkjetprinted silver lines was successfully reduced to 1/3 of the original value using this methodology. Large-area flexible circuits with delicate patterns and good morphology were thus fabricated. The resultant flexible circuits showed excellent electrical conductivity as low as 4.5 Ω/□ and strong tolerance to mechanical bending. The simple methodology is also applicable to substrates with various wettability, which suggests a general strategy to enhance the printing quality of inkjet printing for manufacturing high-performance large-area flexible electronics.

Extrusion-Based 3D-Printed Supercapacitors:Recent Progress and Challenges

Supercapacitors have been regarded as promising power supplies for future electronics due to their high power density,superior stability,easy integration,and safety.Extrusion-based three-dimensional printing technologies hold promise to satisfy the demands for integrated and flexible supercapacitors because of their highly versatile manufacturing process.In this review article,a comprehensive and timely review of these state-of-theart technologies is presented.We start with a brief introduction of fundamental concepts of supercapacitors,including energy storage mechanisms and device structures.Then,the latest progress of extrusionbased three-dimensional printing technologies(e.g.,fused deposition modeling,inkjet printing,and direct ink writing)along with their applications for manufacturing supercapacitors is summarized.The choice of printable materials(e.g.,graphene,carbon nanotubes,metal oxides,and MXenes),printing process,and the resulted electrochemical performances of supercapacitors are especially emphasized.Finally,the development of extrusion-based three-dimensional printing supercapacitors is summarized,with existing challenges diagnosed,possible solutions proposed,and future outlooks forecasted.We hope this review can offer insights to further improve the performance of three-dimensional-printed supercapacitors for practical applications.

Inkjet-Printed Organic Solar Cells and Perovskite Solar Cells: Progress,Challenges, and Prospect

In recent years,the power conversion efficiency of organic solar cells(OSCs)and perovskite(PVSCs)has increased to over 19%and25%,respectively.Meanwhile,the long-term stability of OSCs and PVSCs was also significantly improved with a better understanding of the degradation mechanism and the improvement of materials,morphology,and interface stability.As both the efficiency and lifetime of solar cells are approaching the commercialization limit,fabrication methods for large-area OSCs and PVSCs that can be directly transferred from lab to fab become essential to promote the industrialization of OSCs and PVSCs.Compared with the coating methods,inkjet printing is a mature industrial technology with the advantages of random digital patterning,excellent precision and fast printing speed,which is considered to have great potential in solar cell fabrication.Many efforts have been devoted to developing inkjet-printed OSCs and PVSCs,and much progress has been achieved in the last few years.In this review,we first introduced the working principle of inkjet printing,the rheology requirements of inks,and the behaviors of the droplets.We then summarized the recent research progresses of the inkjet-printed OSCs and PVSCs to facilitate knowledge transfer between the two technologies.In the end,we gave a perspective on inkjet-printed OSCs and PVSCs.

Preparation,Mechanical and Biological Properties of Inkjet Printed Alginate/Gelatin Hydrogel

3D printing has made remarkable progress in soft tissue reconstruction enabling the custom design of complex material implants with patient specific geometry.The aim of this study was to inkjet print mechanically reinforced biocompatible hydrogels.Here,we developed a double crosslinked ink by optimizing the rheological properties of solutions of sodium alginate(NaAlg),NaAlg/transglutaminase(TG),CaCl_(2)and gelatin/CaCl_(2).The results showed that a two-component ink system comprising NaAlg(4%w/v)/TG(0.8%w/v)and gelatin(4%w/v)/CaCl_(2)(3%w/v)gave optimum printability.The mechanical and biological properties of printed alginate/gelatin hydrogels prepared from inks with different gelatin contents,and incorporated fibroblasts,were characterized by Scanning Electron Microscope(SEM),mechanical testing and laser confocal microscopy.The compressive moduli of alginate/gelatin hydrogels could be adjusted from 19.2 kPa±1.2 kPa to 65.9 kPa±3.3 kPa by increasing the content of gelatin.After incubation for 7 d,fibroblasts had permeated all printed hydrogels and the rate of proliferation increased with increasing gelatin content.The highest cell proliferation rate(497%)was obtained in a hydrogel containing 4.5%(w/v)gelatin.This study offers a new strategy for the fabrication of 3D structures used to mimic the function of native tissues.

High performance inkjet-printed QLEDs with 18.3% EQE: improving interfacial contact by novel halogen-free binary solvent system

Poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt(4,4′-(N-(4-butylphenyl))](TFB),one of the most popular and widely used hole-transport layer(HTL)materials,has been successfully applied in high performance spin-coated quantum dots-based light-emitting diodes(QLEDs)due to its suitable energy level and high mobility.However,there are still many challenging issues in inkjet-printed QLED devices when using TFB as HTL.TFB normally suffers from the interlayer mixing and erosion,and low surface energy against the good film formation.Here,a novel environment-friendly binary solvent system was established for formulating quantum dot(QD)inks,which is based on mixing halogen-free alkane solvents of decalin and n-tridecane.The optimum volume ratio for the mixture of decalin and n-tridecane was found to be 7:3,at which a stable ink jetting flow and coffee-ring free QD films could be formed.To research the influence of substrate surface on the formation of inkjet-printed QD films,TFB was annealed at different temperatures,and the optimum annealing temperature was found to enable high quality inkjet-printed QD film.Inkjet-printed red QLED was ultimately manufactured.A maximum 18.3%of external quantum efficiency(EQE)was achieved,reaching 93%of the spin-coated QLED,which is the best reported high efficiency inkjet-printed red QLEDs to date.In addition,the inkjet-printed QLED achieved similar T75 operational lifetime(27 h)as compared to the spin-coated reference QLED(28 h)at 2,000 cd·m−2.This work demonstrated that the novel orthogonal halogen-free alkane co-solvents can improve the interfacial contact and facilitate high-performance inkjet printing QLEDs with high EQE and stability.

Controllable printing of large-scale compact perovskite films for flexible photodetectors

Perovskite materials are promising candidates for the next generation of wearable optoelectronics.However,due to uncontrolled crystallization and the natural brittle property of crystals,it remains a great challenge to fabricate large-scale compact and tough perovskite film.Here we report a facile method to print large-scale perovskite films with high quality for flexible photodetectors.By introducing a soluble polyethylene oxide(PEO)layer during the inkjet printing process,the nucleation and crystal growth of perovskite is well controlled.Perovskite films can be easily printed in large scale and patterned in high resolution.Moreover,this method can be extended to various kinds of perovskite materials,such as MAPbb(MA=methylammonium),MA_(3)Sb_(2)l_(9),and(BA)_(2)PbBr_(4)(BA=benzylammonium).The printed perovskite films show high quality and excellent mechanical performance.The photodetectors based on the MAPbBr3 perovskite films show a responsivity up to -1,036 mAA/V and maintain over 96.8%of the initial photocurrent after 15,000 consecutive bending cycles.This strategy provides a facile approach to prepare large-scale flexible perovskite films.It opens up new opportunities for the fabrication of diverse wearable optoelectronic devices.

Fully inkjet-printed microwave passive electronics

Fully inkjet-printed three-dimensional(3D)objects with integrated metal provide exciting possibilities for on-demand fabrication of radio frequency electronics such as inductors,capacitors,and filters.To date,there have been several reports of printed radio frequency components metallized via the use of plating solutions,sputtering,and low-conductivity pastes.These metallization techniques require rather complex fabrication,and do not provide an easily integrated or versatile process.This work utilizes a novel silver ink cured with a low-cost infrared lamp at only 80℃,and achieves a high conductivity of 1×10^(7) S m^(−1).By inkjet printing the infrared-cured silver together with a commercial 3D inkjet ultraviolet-cured acrylic dielectric,a multilayer process is demonstrated.By using a smoothing technique,both the conductive ink and dielectric provide surface roughness values of <500 nm.A radio frequency inductor and capacitor exhibit state-of-the-art quality factors of 8 and 20,respectively,and match well with electromagnetic simulations.These components are implemented in a lumped element radio frequency filter with an impressive insertion loss of 0.8 dB at 1 GHz,proving the utility of the process for sensitive radio frequency applications.