Organic Solar Cell by Inkjet Printing—An Overview

In recent years, organic solar cells became more attractive due to their flexible power devices and the potential for low-cost manufacturing. Inkjet printing is a very potential manufacturing technique of organic solar cells because of its low material usage, flexibility, and large area formation. In this paper, we presented an overall review on the inkjet printing technology as well as advantages of inkjet-printing, comparison of inkjet printing with other printing technologies and its potential for organic solar cells (OSCs). Here we highlighted in more details about the viability of environment-friendly and cost-effective, non-halogenated indium tin oxide (ITO) free large scale roll to roll production of the OSC by inkjet printing technology. The challenges of inkjet printing like the viscosity limitations, nozzle clogging, coffee ring effect, and limitation of printability as well as dot spacing are also discussed. Lastly, some of the improvement strategies for getting the higher efficiency of the OSCs have been suggested

The Silver Lining: A Novel, Inkjet-Printed Mesh Coplanar-Slot Antenna for the UHF Band

The Federal Communications Commission (FCC) is opening up frequencies within the television range (400MHz to 700MHz) of the Ultra High Frequency (UHF) band for use in emerging technologies, such as cognitive radio networks and machine-to-machine communication. In order for manufacturers to produce affordable antennas that can be used in these emerging technologies, inexpensive antennas are required that meet these new spectrum needs. This paper presents a mesh coplanar-slot bowtie patch antenna fabricated using commercially available inkjet-printing technology. Two antennas were fabricated: a 27x21cm copper FR4 antenna with .25mm lines and a 27x21cm silver antenna with 2mm lines fabricated using inkjet-printing. The copper antenna was iteratively designed in High Frequency Software Simulator (HFSS) and measured using a network analyzer. Simulations and measured results, which show good agreement, verify the viability of merging the mesh and coplanar-slot topologies. The silver antenna is a variation of the copper antenna that was iteratively altered in HFSS until the desired bandwidth was achieved. Simulations and measured results, which show good agreement, verify the viability of inkjet-printing as a fabrication method. The radioelectrical performance of the antennas were also compared to each other. Although there was slight variation between the resonant frequency and bandwidth, an adequate agreement was observed between the two antennas. This demonstrates the feasibility of using inkjet-printing as a quick, efficient method to fabricate UHF antennas that can take advantage of emerging spectrum and be used in applications such as cognitive-radio-networks and machine-to-machine communication.https://scholarscompass.vcu.edu/uresposters/1274/thumbnail.jp

Material Interactions and Self-Assembly in Inkjet Printing

Inkjet printing has attracted much attention in recent years as a versatile manufacturing tool, suitable for printing functional materials. This facile, low-cost printing technique with high throughput and accuracy is considered promising for a wide range of applications including but not limited to optical and electronic devices, sensors, solar cells, biochips, and displays. The performance of such functional devices is significantly influenced by the deposit morphology and printing resolution. Therefore, fabrication functional devices with precise footprints by inkjet printing requires deep understanding of ink properties, material interactions, and material self-assembly. In conventional inkjet printing process, where sessile droplets are directly printed on substrates, particle depositions are usually associated with the well-known, undesirable coffee-ring effect due to the high solvent evaporation rate at the edges of the printed droplets. Such particle accumulation phenomenon in vicinity of the three-phase contact lines of sessile droplets is considered detrimental to inkjet printing applications. This study investigates the material interactions and self-assembly of colloidal inks in inkjet printing applications at different length scales. The potential of inkjet printing has been exploited through employing the dual-droplet inkjet printing of colloidal particles to investigate the self-assembly of colloidal nanoparticles at the air-liquid interface and at the three-phase contact line of sessile droplets, which provide better understanding of the particle deposition morphologies after solvent evaporation. Different from conventional inkjet printing, the dual-droplet printing involves jetting wetting droplets, containing colloidal nanoparticles dispersed in solvents with high vapor pressure, over supporting droplets composed of water only. By tuning the surface tensions and controlling the jetting parameters of the jetted droplets, monolayers with closely-packed deposition of colloidal nanoparticles are demonstrated. Various solutions are proposed to totally suppress or mitigate the coffee-ring effect in inkjet printing applications through tuning the pH value of the supporting droplets in the dual-droplet inkjet printing to control the multibody interactions (i.e., particle-particle, particle-interface, and particle-substrate interactions) or by applying magnetic field to direct the self-assembly of colloidal particles in conventional inkjet printing. In addition, the influence of various forces such as drag force, van der Waals force, electrotactic force, and capillary force on the particle deposition and assembly in vicinity of the three-phase contact line area were investigated for both the conventional and dual-droplet inkjet printing techniques. Finally, fabrication of functional devices such as stretchable conductors have also been demonstrated by inkjet printing of silver nanowires into elastomer substrate, where the viscous liquid elastomer layer shaped the printed silver wire lines into tens of micrometers in dimeter. The silver nanowires align along the printing direction during solvent evaporation, resulting in wires with good mechanical stability and electrical performance. The printing techniques and the outcomes presented in this study can be harnessed in engineering and manufacturing a wide range of technological applications ranging from high-performance optical and electronic devices to stretchable conductors and sensors

Combinatorial screening of functional polymers for organic electronics via inkjet printing

Inkjet printing represents a solution deposition technique that is characterized by its non-contact, material-efficient and reproducible processing. It is, however, a long way to gain a full understanding of the complete drying process, since the process conditions as well as the ink properties correlate in a complex relation with the final device properties. For inkjet printing, all solute parameters have a significant influence on the preparation of the printed patterns, which makes the ink development crucial. Important factors include the contact angle, ink viscosity and surface tension as well as the nozzle diameter. By using multiple print heads, a high speed production of thin films can be performed. Therefore, inkjet printing can be used as a R2R coating technique. However, for the application of inkjet printing in a commercial available device, there are many challenges to overcome, which is the reason why inkjet printing is up to now mainly used in scientific research environment. For a detailed understanding of the preparation techniques as well as to evaluate whether inkjet printing has the potential for producing efficient devices, the drying processes and resulting film morphologies need to be well understood. This thesis provides an overview of methodical investigations of ink characteristics, printing conditions and final film properties. In particular, the possibility to integrate inkjet printing into a combinatorial screening workflow evolves inkjet printing to a notable method for an efficient screening of new materials for organic electronics applications like organic photovoltaics (OPVs), organic light emitting diodes (OLEDs) and organic radical batteries (ORBs)

All inkjet-printed graphene-based conductive patterns for wearable e-textile applications

© 2017 The Royal Society of Chemistry. Inkjet printing of graphene inks is considered to be very promising for wearable e-textile applications as benefits of both inkjet printing and extra-ordinary electronic, optical and mechanical properties of graphene can be exploited. However, the common problem associated with inkjet printing of conductive inks on textiles is the difficulty to print a continuous conductive path on a rough and porous textile surface. Here we report inkjet printing of an organic nanoparticle based surface pre-treatment onto textiles to enable all inkjet-printed graphene e-textiles for the first time. The functionalized organic nanoparticles present a hydrophobic breathable coating on textiles. Subsequent inkjet printing of a continuous conductive electrical path onto the pre-treated coating reduced the sheet resistance of graphene-based printed e-textiles by three orders of magnitude from 1.09 × 106 Ω sq-1 to 2.14 × 103 Ω sq-1 compared with untreated textiles. We present several examples of how this finding opens up opportunities for real world applications of printed, low cost and environmentally friendly graphene wearable e-textiles

Predicting pharmaceutical inkjet printing outcomes using machine learning

Inkjet printing has been extensively explored in recent years to produce personalised medicines due to its low cost and versatility. Pharmaceutical applications have ranged from orodispersible films to complex polydrug implants. However, the multi-factorial nature of the inkjet printing process makes formulation (e.g., composition, surface tension, and viscosity) and printing parameter optimization (e.g., nozzle diameter, peak voltage, and drop spacing) an empirical and time-consuming endeavour. Instead, given the wealth of publicly available data on pharmaceutical inkjet printing, there is potential for a predictive model for inkjet printing outcomes to be developed. In this study, machine learning (ML) models (random forest, multilayer perceptron, and support vector machine) to predict printability and drug dose were developed using a dataset of 687 formulations, consolidated from in-house and literature-mined data on inkjet-printed formulations. The optimized ML models predicted the printability of formulations with an accuracy of 97.22%, and predicted the quality of the prints with an accuracy of 97.14%. This study demonstrates that ML models can feasibly provide predictive insights to inkjet printing outcomes prior to formulation preparation, affording resource- and time-savings

Fem of electrospinning compared to inkjet printing model

Electrospinning is a process that uses electrostatic forces to produce nanofibers, or fibers in the nano scale. Nanofibers are widely used in many fields like drug delivery and tissue engineering. Nowadays, it is gaining much attention in the research community as an advantageous process. However, there are many parameters that controlnanofiber formation. This research intends to develop a model of electrospinning on the basis of an inkjet printer technique by using a computer aided simulation (COMSOL). Inkjet printing is a technique that delivers small volumes at high repetitions which can betransported by electrostatic forces through the air onto their intended target. The similarity of electrospinning and inkjet printing can be seen in the method of delivering the solution whether it is ink or a polymer to its intended target. Inkjet printing technique is controlled and reproducible while electrospinning has a certain level of control which creates variability from lot-to-lot. Taking the combined parameters of inkjet printing and electrospinning can help create more controlled experiments and reproducible results

INKJET PRINTING OF THREE-DIMENSIONAL VASCULAR-LIKE CONSTRUCTS FROM CELL SUSPENSIONS

Inkjet printing has found an increasing number of biofabrication applications, specifically organ printing, which has been emerging as a promising solution to the organ donor shortage. While some studies have been conducted to investigate various engineering problems associated with DOD inkjet printing of biological material-based fluids, the pinch-off, the cell-laden droplet formation, the effects of electric field on droplet formation, and challenges in 3D vascular-like construct fabrication haven\u27t been systematically investigated. The objective of this study is to investigate the pinch-off, the cell-laden droplet formation, the effects of electric field on droplet formation, and manufacturing challenges during fabrication using DOD inkjet printing. The pinch-off process during DOD inkjet printing of viscoelastic alginate solutions is systematically investigated by studying the effects of sodium alginate (NaAlg) concentration and operating conditions on the pinch-off. It is found that there are four types of pinch-off during DOD inkjet printing of viscoelastic NaAlg solutions: front-pinching, exit-pinching, hybrid-pinching and middle-pinching. In particular, front-pinching is governed by a balance of inertial and capillary stresses, while exit-pinching is governed by a balance of elastic and capillary stresses. An operating diagram is constructed with respect to the Weber number and a proposed J number to classify regimes for different types of pinch-off. The cell-laden droplet formation is studied and compared with the droplet formation of polystyrene bead-based suspensions. It is found that the breakup time increases but the droplet size, droplet velocity, and number of satellites decrease as the cell concentration increases. Compared to the polystyrene bead-based suspension, the ejected fluid volume is less, the droplet velocity is smaller, and the breakup time is longer using the cell-laden bioink. The electric field-assisted droplet formation under piezoactuation-based DOD inkjet printing is investigated. It is found that droplet velocity increases and the droplet size decreases with the increase of the applied voltage. Pinch-off locations may vary depending on the applied voltage. The combination effect of the electric field and meniscus oscillation can be utilized to significantly reduce the droplet diameter. The electric field extends the capability of DOD inkjet printing to bioinks with high cell concentrations. The gained knowledge of DOD inkjet printing has been further applied to vertical and horizontal printing of 3D vascular-like constructs using cell-laden bioink. It is found that the maximum achievable height of overhang structure depends on the inclination angle during vertical printing. To overcome the deformation-induced construct defect during horizontal printing, a predictive compensation approach has been proposed to fabricate 3D tubular constructs horizontally. Alginate cellular tubes have also been successfully printed with a satisfactory post-printing cell viability of 87% immediately after printing and after 24 hours of incubation. Overall, this dissertation provides a better understanding of the pinch-off of viscoelastic alginate solutions, cell-laden droplet formation, effect of electric field on droplet formation under piezoactuation-based DOD inkjet printing, and fabrication process of 3D vascular-like constructs from bioink. This work would help better fabricate tissue-engineered blood vessels with a complex geometry using DOD inkjet printing

Process-Property Linkages Construction for Inkjet Printing with Machine Learning

Printed electronics are emerging technologies that can potentially revolutionize the manufacturing of electronic devices. One promising technology for printed electronics is inkjet printing. Inkjet printing offers both low-cost processing and high resolution. Being a subset of additive manufacturing, inkjet printing minimizes waste and is compatible with a wide range of inks. However, inkjet printing of electronic devices is still in its infancy. One major challenge for inkjet printing is the complexity of the process optimization and uncertain high throughput production. To achieve a high-quality print, there is a complex parameter space of materials and processing parameters that needs to be optimized. To address this challenge, in this thesis work, we develop a machine learning algorithm to connect the processing parameters to print morphology for inkjet processes. To achieve this goal, we developed more than 200 experimental samples and processed the print images automatically with OpenCV-based codes. Finally, we correlated the morphology specifications, i.e., print line width, overspray, and roughness to the processing parameters, i.e., cartridge height, nozzle voltage, and drop spacing, via a neural network model. The order of machine learning model accuracy from high to low is for line width, roughness, and overspray, respectively. The model\u27s low predictability of overspray can be attributed to our limited dataset, Dimatix unreliable performance, or the low dependency of overspray on the processing parameters of this study