Degradation of all-inkjet-printed organic thin-film transistors with TIPS-pentacene under processes applied in textile manufacturing

Printed electronics represent an alternative solution for the manufacturing of low-temperature and large area flexible electronics. The use of inkjet printing is showing major advantages when compared to other established printing technologies such as gravure, screen or offset printing, allowing the reduction of manufacturing costs due to its efficient material usage and the direct-writing approach without requirement of any masks. However, several technological restrictions for printed electronics can hinder its application potential, e.g. the device stability under atmospheric or even more stringent conditions. Here, we study the influence of specific mechanical, chemical, and temperature treatments usually appearing in manufacturing processes for textiles on the electrical performance of all-inkjet-printed organic thin-film transistors (OTFTs). Therefore, OTFTs where manufactured with silver electrodes, a UV curable dielectric, and 6,13-bis(triisopropylsilylethynyl) pentance (TIPS-pentacene) as the active semiconductor layer. All the layers were deposited using inkjet printing. After electrical characterization of the printed OTFTs, a simple encapsulation method was applied followed by the degradation study allowing a comparison of the electrical performance of treated and not treated OTFTs. Industrial calendering, dyeing, washing and stentering were selected as typical textile processes and treatment methods for the printed OTFTs. It is shown that the all-inkjet-printed OTFTs fabricated in this work are functional after their submission to the textiles processes but with degradation in the electrical performance, exhibiting higher degradation in the OTFTs with shorter channel lengths (L = 10 μm).     

高精度数码喷墨打印技术及在印刷电子上的应用

文章介绍了高精度数码喷墨打印技术的设备,材料和打印工艺及其在印刷电子上的应用。重点介绍了纳米银墨水的结构、性能、烧结条件和电性能以及打印性能及其在制备导电线路上的应用,探讨了喷头孔径及基材的表面性能对打印线路的影响。最后,介绍了挠性PCB的打印。     

A Room‐Temperature High‐Conductivity Metal Printing Paradigm with Visible‐Light Projection Lithography

Fabricating electronic devices require integrating metallic conductors and polymeric insulators in complex structures. Current metal‐patterning methods such as evaporation and laser sintering require vacuum, multistep processes, and high temperature during sintering or postannealing to achieve desirable electrical conductivity, which damages low‐temperature polymer substrates. Here reports a facile ecofriendly room‐temperature metal printing paradigm using visible‐light projection lithography. With a particle‐free reactive silver ink, photoinduced redox reaction occurs to form metallic silver within designed illuminated regions through a digital mask on substrate with insignificant temperature change (<4 °C). The patterns exhibit remarkably high conductivity achievable at room temperature (2.4 × 10⁷ S m^?1, ≈40% of bulk silver conductivity) after simple room‐temperature chemical annealing for 1–2 s. The finest silver trace produced reaches 15 µm. Neither extra thermal energy input nor physical mask is required for the entire fabrication process. Metal patterns were printed on various substrates, including polyethylene terephthalate, polydimethylsiloxane, polyimide, Scotch tape, print paper, Si wafer, glass coverslip, and polystyrene. By changing inks, this paradigm can be extended to print various metals and metal–polymer hybrid structures. This method greatly simplifies the metal‐patterning process and expands printability and substrate materials, showing huge potential in fabricating microelectronics with one system.     

3D‐Printed All‐Fiber Li‐Ion Battery toward Wearable Energy Storage

Conventional bulky and rigid power systems are incapable of meeting flexibility and breathability requirements for wearable applications. Despite the tremendous efforts dedicated to developing various 1D energy storage devices with sufficient flexibility, challenges remain pertaining to fabrication scalability, cost, and efficiency. Here, a scalable, low‐cost, and high‐efficiency 3D printing technology is applied to fabricate a flexible all‐fiber lithium‐ion battery (LIB). Highly viscous polymer inks containing carbon nanotubes and either lithium iron phosphate (LFP) or lithium titanium oxide (LTO) are used to print LFP fiber cathodes and LTO fiber anodes, respectively. Both fiber electrodes demonstrate good flexibility and high electrochemical performance in half‐cell configurations. All‐fiber LIB can be successfully assembled by twisting the as‐printed LFP and LTO fibers together with gel polymer as the quasi‐solid electrolyte. The all‐fiber device exhibits a high specific capacity of ≈110 mAh g^?1 at a current density of 50 mA g^?1 and maintains a good flexibility of the fiber electrodes, which can be potentially integrated into textile fabrics for future wearable electronic applications.     

Inkjet printed silver nanowire percolation networks as electrodes for highly efficient semitransparent organic solar cells

In this work, we demonstrate inkjet printing of silver nanowires (AgNW) with an average length of 10's of μm using industrial printheads with nozzle diameters in the same size range. The printed silver nanowire mesh reveals uniform distribution and a good balance between conductivity and transmittance, which is comparable to layers fabricated by conventional methods like slot-die or spray coating. Employing a novel AgNW ink formulation based on a high boiling alcohol allows printing directly on PEDOT:PSS and prevents nozzle clogging. Using silver nanowire meshes as bottom and top electrodes, a fully inkjet printed semitransparent organic solar cell with a power conversion efficiency of 4.3% for 1 cm² area is demonstrated, which is the highest value reported so far for fully inkjet printed organic photovoltaic cells.     

R2R gravure and inkjet printed RF resonant tag

The fabrication of passive circuitry by gravure and inkjet printing is studied. A chipless inductively coupled RF resonant tag is analyzed as a test structure. A floating-bridge layout is employed to provide high yield when fabricated by roll-to-roll (R2R) printing. The conducting first layer and insulating second layer are R2R gravure printed with silver nanoparticle ink and a thermally cross-linkable dielectric ink, respectively. Above 10 MS/m conductivity is obtained for the first layer, which passes three times through the 5 m long drying unit at 5 m/min speed. The floating bridge is inkjet printed with silver nanoparticle ink and the prototype tag is measured over a reading distance of ca. 2 cm. An equivalent circuit model is presented and the model parameters are optimized to obtain a best fit to the measured frequency response. This indirect measurement provides an estimate of 4.3 μm for the thickness of the dielectric layer sandwiched between the conducting top and bottom layers. Application possibilities for the all-printed RF resonant tag are outlined.     

Inkjet Printing of Self‐Assembled 2D Titanium Carbide and Protein Electrodes for Stimuli‐Responsive Electromagnetic Shielding

2D titanium carbides (MXene) possess significant characteristics including high conductivity and electromagnetic interference shielding efficiency (EMI SE) that are important for applications in printed and flexible electronics. However, MXene‐based ink formulations are yet to be demonstrated for proper inkjet printing of MXene patterns. Here, tandem repeat synthetic proteins based on squid ring teeth (SRT) are employed as templates of molecular self‐assembly to engineer MXene inks that can be printed as stimuli‐responsive electrodes on various substrates including cellulose paper, glass, and flexible polyethylene terephthalate (PET). MXene electrodes printed on PET substrates are able to display electrical conductivity values as high as 1080 ± 175 S cm^?1, which significantly exceeds electrical conductivity values of state‐of‐the‐art inkjet‐printed electrodes composed of other 2D materials including graphene (250 S cm^?1) and reduced graphene oxide (340 S cm^?1). Furthermore, this high electrical conductivity is sustained under excessive bending deformation. These flexible electrodes also exhibit effective EMI SE values reaching 50 dB at films with thicknesses of 1.35 µm, which mainly originate from their high electrical conductivity and layered structure.     

Environmental protection of inkjet-printed Ag conductors

Electrically conductive silver nanoparticle ink patterns were fabricated using the inkjet printing method. Two different polymer films were used as the substrate materials. The patterns were exposed to humidity and salt fog and the electrical performance (sheet resistance and RF performance) as well as mechanical endurance (adhesion) were measured before and after the environmental tests. The electrical properties of the printed structures remained good in all the measurable samples. The adhesion between the ink and a substrate material appeared to be a greater challenge in harsh environments. Protection capabilities of one dip coated and one hot laminated barrier materials were evaluated during the environmental tests. The results showed that there is a need for environmental protection in printed electronics. Especially the laminated barrier films can offer a potential solution for shielding printed electronics in harsh environments as they can provide good mechanical protection, and can easily be integrated in roll-to-roll process.     

Textile‐Based Flexible Electroluminescent Devices

Flexible and transparent textile‐based conductors are developed by inkjet printing poly(3,4‐ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) onto polyethylene terephthalate (PET) mesh fabrics. The conductivity–transparency relationship is determined for textile‐based conductors with different thicknesses of the printed PEDOT:PSS film. The function of these textile‐based conductors is studied in the alternating current powder electroluminescent (ACPEL) devices and compared with indium tin oxide (ITO) glass in an ACPEL device of the same configuration. Textiles coated with conducting polymers are a potential alternative to coated polymer films for flexible, transparent conductors.     

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.     

A benchmark study of commercially available copper nanoparticle inks for application in organic electronic devices

A set of three commercial copper nanoparticle based inkjet inks has been benchmarked with respect to their potential to form conducting printed structures for future applications in organic electronic devices. Significant differences were observed in terms of jetting properties, spreading behaviour and line formation on a number of relevant substrates. The inks' stabilities against oxidation were investigated, inkjet printed patterns were subjected to photonic flash sintering and their electrical properties characterized. As a result, optimized conditions for printing and post-deposition processing were determined. Photonic flash sintering, which is a roll-to-roll compatible manufacturing process, allowed a significant reduction in sintering time. Flash sintering was performed in the presence of air, thereby excluding the necessity for processing under inert atmosphere. One product was identified which showed satisfactory performances regarding all tested features: stable jet formation, well-defined definition of the printed structures and high electrical conductivity (20% of the value of bulk Cu). The obtained results can be considered as a promising step towards the future application of Cu inks in organic electronic devices.     

Self‐Organization of Inkjet‐Printed Organic Semiconductor Films Prepared in Inkjet‐Etched Microwells

The high‐precision deposition of highly crystalline organic semiconductors by inkjet printing is important for the production of printed organic transistors. Herein, a facile nonconventional lithographic patterning technique is developed for fabricating banks with microwell structures by inkjet printing solvent droplets onto a polymer layer, thereby locally dissolving the polymer to form microwells. The semiconductor ink is then inkjet‐printed into the microwells. In addition to confining the inkjet‐printed organic semiconductor droplets, the microwells provide a platform onto which organic semiconductor molecules crystallize during solvent evaporation. When printed onto the hydrophilic microwells, the inkjet‐printed 6,13‐bis(triisopropylsilylethynyl) pentacene (TIPS_PEN) molecules undergo self‐organization to form highly ordered crystalline structures as a result of contact line pinning at the top corner of the bank and the outward hydrodynamic flow within the drying droplet. By contrast, small crystallites form with relatively poor molecular ordering in the hydrophobic microwells as a result of depinning of the contact line along the walls of the microwells. Because pinning in the hydrophilic microwells occurred at the top corner of the bank, treating the surfaces of the dielectric layer with a hydrophobic organic layer does not disturb the formation of the highly ordered TIPS_PEN crystals. Transistors fabricated on the hydrophilic microwells and the hydrophobic dielectric layer exhibit the best electrical properties, which is explained by the solvent evaporation and crystallization characteristics of the organic semiconductor droplets in the microwell. These results indicate that this technique is suitable for patterning organic semiconductor deposits on large‐area flexible substrates for the direct‐write fabrication of high‐performance organic transistors.     

Additive Manufacturing of Batteries

Additive manufacturing, i.e., 3D printing, is being increasingly utilized to fabricate a variety of complex‐shaped electronics and energy devices (e.g., batteries, supercapacitors, and solar cells) due to its excellent process flexibility, good geometry controllability, as well as cost and material waste reduction. In this review, the recent advances in 3D printing of emerging batteries are emphasized and discussed. The recent progress in fabricating 3D‐printed batteries through the major 3D‐printing methods, including lithography‐based 3D printing, template‐assisted electrodeposition‐based 3D printing, inkjet printing, direct ink writing, fused deposition modeling, and aerosol jet printing, are first summarized. Then, the significant achievements made in the development and printing of battery electrodes and electrolytes are highlighted. Finally, major challenges are discussed and potential research frontiers in developing 3D‐printed batteries are proposed. It is expected that with the continuous development of printing techniques and materials, 3D‐printed batteries with long‐term durability, favorable safety as well as high energy and power density will eventually be widely used in many fields.     

Three‐Dimensional Inkjet‐Printed Interconnects using Functional Metallic Nanoparticle Inks

Inkjet‐printed gold nanoparticle pillars are investigated as a high‐performance alternative to conventional flip‐chip interconnects for electronic packages, with significant advantages in terms of mechanical/chemical robustness and conductivity. The process parameters critical to pillar fabrication are described and highly uniform pillar arrays are demonstrated. More generally, this work underscores the impact of sintering on the electrical, mechanical, structural, and compositional properties of three‐dimensional nanoparticle‐based structures. Using heat treatments as low as 200 °C, electrical and mechanical performance that outcompetes conventional lead‐tin eutectic solder materials is achieved. With sintering conditions reaching 300 °C it is possible to achieve pillars with properties comparable to bulk gold. This work demonstrates the immense potential for both inkjet printing and metal nanoparticles to become a viable and cost‐saving alternative to both conventional electronic packaging processes and application‐specific integration schemes.     

Fully solution-processed organic thin-film transistors by consecutive roll-to-roll gravure printing

A high-performance/flexible organic thin-film transistor (OTFT) is fabricated by using all-step solution processes, which are composed of roll-to-roll gravure, plate-to-roll gravure and inkjet printing with the least process number of 5. Roll-to-roll gravure printing is used to pattern source/drain electrodes on plastic substrate while semiconductor and dielectric layers are printed by consecutive plate-to-roll gravure printing. Finally, inkjet printing of Ag organometallic ink is used to pattern the gate electrode. The fabricated OTFT exhibits excellent electrical performance, field-effect mobility over 0.2 cm²/Vs, which is one of the best compared to the previous works. The deposition of a self-assembled monolayer on the source-drain electrodes results in a higher work function which is suitable for a p-type polymer semiconductor. Moreover, the formation of dense gate electrode line on hydrophobic dielectric is achieved by selecting suitable Ag ink.     

Inkjetting dielectric layer for electronic applications

Printed electronics is expected to increase its market share significantly in near future. The emerging applications include e.g. display applications, RFID tags, and photovoltaic applications. A benefit of printing is the additive character of the process, which means that material is deposited only the amount that is needed. Digital printing increases flexibility of the process, because circuits are manufactured directly from a digital file, which removes need of fixed masks or patterned screens for each layout. Formation of a multilayer circuitry requires printing of conductive and insulative layers. This paper focuses on printing of a dielectric layer with an inkjet printer. Six sigma DMAIC approach was applied during the process characterization and analysis. The study began by defining the process parameters and evaluating their importance to the outputs. Highest rated parameters were taken into consideration and a design of experiments was established. Measured values were analyzed and it was observed which parameters had the highest effect on the outputs. The results were further verified and it was observed that electrically the printed structures were successful.     

Highly Customizable All Solution–Processed Polymer Light Emitting Diodes with Inkjet Printed Ag and Transfer Printed Conductive Polymer Electrodes

Inkjet and transfer printing processes are combined to easily form patterned poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) films as top anodes of all solution–processed inverted polymer light emitting diodes (PLEDs) on rigid glass and flexible plastic substrates. An adhesive PEDOT:PSS ink is formulated and fully customizable patterns are obtained using the inkjet printing process. In order to transfer the patterned PEDOT:PSS films, adhesion properties at interfaces during multistep transfer printing processes are carefully adjusted. The transferred PEDOT:PSS film on the plastic substrates shows not only a sheet resistance of 260.6 Ω/□ and a transmittance of 92.1% at 550 nm wavelength but also excellent mechanical flexibility. The PLEDs with spin‐coated functional layers sandwiched between the transferred PEDOT:PSS top anodes and inkjet‐printed Ag bottom cathodes are fabricated. The fabricated PLEDs on the plastic substrates show a high current efficiency of 10.4 cd A^?1 and high mechanical stability. It is noted that because both Ag and PEDOT:PSS electrodes can be patterned with a high degree of freedom via the inkjet printing process, highly customizable PLEDs with various pattern sizes and shapes are demonstrated on the glass and plastic substrates. Finally, with all solution process, a 5 × 7 passive matrix PLED array is demonstrated.     

Inkjet Printing of a Highly Loaded Palladium Ink for Integrated,Low‐Cost pH Sensors

An inkjet printing process for depositing palladium (Pd) thin films from a highly loaded ink (>14 wt%) is reported. The viscosity and surface tension of a Pd‐organic precursor solution is adjusted using toluene to form a printable and stable ink. A two‐step thermolysis process is developed to convert the printed ink to continuous and uniform Pd films with good adhesion to different substrates. Using only one printing pass, a low electrical resistivity of 2.6 μΩ m of the Pd film is obtained. To demonstrate the electrochemical pH sensing application, the surfaces of the printed Pd films are oxidized for ion‐to‐electron transduction and the underlying layer is left for electron conduction. Then, solid‐state reference electrodes are integrated beside the bifunctional Pd electrodes by inkjet printing. These potentiometric sensors have sensitivities of 60.6 ± 0.1 and 57 ± 0.6 mV pH^?1 on glass and polyimide substrates, and short response times of 11 and 6 s, respectively. Also, accurate pH values of real water samples are obtained by using the printed sensors with a low‐cost multimeter. These results indicate that the facile and cost‐effective inkjet printing and integration techniques may be applied in fabricating future electrochemical monitoring systems for environmental parameters and human health conditions.     

Printed Transistors on Paper: Towards Smart Consumer Product Packaging

The integration of fully printed transistors on low cost paper substrates compatible with roll‐to‐roll processes is demonstrated here. Printed electronics promises to enable a range of technologies on paper including printed sensors, RF tags, and displays. However, progress has been slow due to the paper roughness and ink absorption. This is solved here by employing gravure printing to print local smoothing pads that also act as an absorption barrier. This innovative local smoothing process retains desirable paper properties such as foldability, breathability, and biodegradability outside of electronically active areas. Atomic force microscopy measurements show significant improvements in roughness. The polymer ink and printing parameters are optimized to minimize ink absorption and printing artifacts when printing the smoothing layer. Organic thin film transistors (OTFT) are fabricated on top of this locally smoothed paper. OTFTs exhibit performance on par with previously reported printed transistors on plastic utilizing the same materials system (pBTTT semiconductor, poly‐4‐vinylphenol dielectric). OTFTs deliver saturation mobility approaching 0.1 cm²V^–1s^–1 and on‐off‐ratio of 3.2 × 10⁴. This attests to the quality of the local smoothing, and points to a promising path for realizing electronics on paper.