High Power Conversion Efficiency of 13.61% for 1 cm2 Flexible Polymer Solar Cells Based on Patternable and Mass-Producible Gravure-Printed Silver Nanowire Electrodes

With the aim of developing high-performance flexible polymer solar cells, the preparation of flexible transparent electrodes (FTEs) via a high-throughput gravure printing process is reported. By varying the blend ratio of the mixture solvent and the concentration of the silver nanowire (AgNW) inks, the surface tension, volatilization rate, and viscosity of the AgNW ink can be tuned to meet the requirements of gravure printing process. Following this method, uniformly printed AgNW films are prepared. Highly conductive FTEs with a sheet resistance of 10.8 Ω sq⁻¹ and a high transparency of 95.4% (excluded substrate) are achieved, which are comparable to those of indium tin oxide electrode. In comparison with the spin-coating process, the gravure printing process exhibits advantages of the ease of large-area fabrication and improved uniformity, which are attributed to better ink droplet distribution over the substrate. 0.04 cm² polymer solar cells based on gravure-printed AgNW electrodes with PM6:Y6 as the photoactive layer show the highest power conversion efficiency (PCE) of 15.28% with an average PCE of 14.75 ± 0.35%. Owing to the good uniformity of the gravure-printed AgNW electrode, the highest PCE of 13.61% is achieved for 1 cm² polymer solar cells based on the gravure-printed FTEs.     

Inkjet‐Printed Single‐Droplet Organic Transistors Based on Semiconductor Nanowires Embedded in Insulating Polymers

Fabrication of organic field‐effect transistors (OFETs) using a high‐throughput printing process has garnered tremendous interest for realizing low‐cost and large‐area flexible electronic devices. Printing of organic semiconductors for active layer of transistor is one of the most critical steps for achieving this goal. The charge carrier transport behavior in this layer, dictated by the crystalline microstructure and molecular orientations of the organic semiconductor, determines the transistor performance. Here, it is demonstrated that an inkjet‐printed single‐droplet of a semiconducting/insulating polymer blend holds substantial promise as a means for implementing direct‐write fabrication of organic transistors. Control of the solubility of the semiconducting component in a blend solution can yield an inkjet‐printed single‐droplet blend film characterized by a semiconductor nanowire network embedded in an insulating polymer matrix. The inkjet‐printed blend films having this unique structure provide effective pathways for charge carrier transport through semiconductor nanowires, as well as significantly improve the on‐off current ratio and the environmental stability of the printed transistors.     

Inkjet Process for Conductive Patterning on Textiles: Maintaining Inherent Stretchability and Breathability in Knit Structures

In this work, a novel technique of inkjet printing e‐textiles with particle free reactive silver inks on knit structures is developed. The inkjet‐printed e‐textiles are highly conductive, with a sheet resistance of 0.09 Ω sq^‐1, by means of controlling the number of print passes, annealing process, and textile structures. It is notable that the inkjet process allows textiles to maintain its inherent properties, including stretchability, flexibility, breathability, and fabric hand after printing process. This is achieved by formation of ultrathin silver layers surrounding individual fibers. The silver layers coated on fibers range from 250 nm to 2.5 µm, maintaining the size of interstices and flexibility of fibers. The annealing process, structure of fibers, and printed layers significantly influence the electrical conductivity of the patterned structures on textiles. Outstanding electrical conductivity and durability are demonstrated by optimizing print passes, controlling textile structures, and incorporating an in situ annealing process. The electrical resistance dependence on the strain rate of the textiles is examined, showing the ability to maintain electrical conductivity to retain light‐emitting diode use, stable more than 500 consecutive strain cycles. Most importantly, inkjet‐printed e‐textiles maintain their characteristic washability, breathability, and fabric hands for applications in wearable technology.     

Multi‐Length Scaled Silver Nanowire Grid for Application in Efficient Organic Solar Cells

Transparent conducting electrodes (TCEs) with multi‐length scaled structure are promising candidates as a potential replacement for indium tin oxide (ITO). In this work, multi‐length scaled silver nanowire (AgNW) grids are demonstrated as TCEs for organic solar cells. The multi‐length scale silver nanowire grids are prepared by top‐down patterning using a neutral vapor etching process. Patterning AgNW film into multi‐length scale grid structures could improve the optical transmittance and enhance the use of incident photons. Based on these multi‐length scale AgNW grids, inverted bulk heterojunction polymer solar cells with power conversion efficiency up to 9.02% are fabricated, which are higher than that based on the original AgNW films and comparable to that based on ITO.     

Solution processable PEDOT:PSS based hybrid electrodes for organic field effect transistors

We report high performance solution processed conductive inks used as contact electrodes for printed organic field effect transistors (OFETs). Poly(3,4-ethylenedioxythiophene): polystyrene sulfonate (PEDOT:PSS) electrodes show highly improved very low sheet resistance of 65.8 ± 6.5 Ω/square (Ω/□) by addition of dimethyl sulfoxide (DMSO) and post treatment with methanol (MeOH) solvent. Sheet resistance was further improved to 33.8 ± 8.6 Ω/□ by blending silver nanowire (AgNW) with DMSO doped PEDOT:PSS. Printed OFETs with state of the art diketopyrrolopyrrole-thieno[3,2-b]thiophene (DPPT-TT) semiconducting polymer were demonstrated with various solution processable conductive inks, including bare, MeOH treated PEDOT:PSS, single wall carbon nanotubes, and hybrid PEDOT:PSS-AgNW, as the source and drain (S/D) electrode by spray printing using a metal shadow mask. The highest field effect mobility, 0.49 ± 0.03 cm² V⁻¹ s⁻¹ for DPPT-TT OFETs, was obtained using blended AgNW with DMSO doped PEDOT:PSS S/D electrode.     

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.     

Micromolding in capillaries and microtransfer printing of silver nanoparticles as soft-lithographic approach for the fabrication of source/drain electrodes in organic field-effect transistors

Within the past years there has been much effort in developing and improving new techniques for the processing of advanced functional materials used in promising applications like micro-optics or organic electronics. Much attention has been paid to solution-based techniques, which enable low-cost processing and new possible developments like flexible displays or inkjet printed electronics. An alternative approach to inkjet printing is soft-lithography, which is a collective term for a number of non-photolithographic techniques and has become an important tool for the micron-sized structuring of materials.Here we report on the use of micromolding in capillaries (MIMIC) and microtransfer printing (μTP) as two soft-lithographic techniques for the fabrication of silver source/drain electrodes in well-performing bottom-gate/bottom-contact organic field-effect transistors (OFETs) with poly(3-hexylthiophene) as active layer material.While MIMIC combines solution-processability with high lateral resolution for highly accurate patterns, μTP is the miniaturized counterpart to conventional letterpress printing.The performance of the OFETs fabricated with these techniques is similar to devices based on conventional gold source/drain electrodes with well-defined source-to-drain current saturation and a linear behavior at low drain voltages suggesting a low contact resistance and hence good carrier injection from the silver electrodes into the organic semiconductor.     

Efficient flexible organic photovoltaics using silver nanowires and polymer based transparent electrodes

Planarization and filling voids between wires are key issues when using nanowire electrodes in flexible solar cells such as organic photovoltaics (OPV). For this purpose, we use poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) which leads to an electrically well connected silver nanowire (AgNW) network. Furthermore, the use of water based PEDOT: PSS leads to humidity assisted AgNW fusing, resulting in a maximum processing temperature of only 120 °C. OPV cells using this AgNW/PEDOT: PSS transparent electrodes exhibit power conversion efficiencies up to 7.15%. Moreover, OPV devices on PET substrates with an alumina encapsulation and barrier adhesive show excellent mechanical flexibility.     

Flexible organic phototransistors based on a combination of printing methods

Highly photosensitive organic phototransistors (OPTs) are successfully demonstrated on a flexible substrate using all-solution process as well as a combination of printing methods which consist of roll-to-plate reverse offset printing (ROP), inkjet printing and bar coating. Excellent electrical switching characteristics are obtained from heterogeneous interfacial properties of the reverse-offset-printed silver nanoparticle electrode and the inkjet-printed p-channel polymeric semiconductor. In particular, the OPTs exhibit remarkably photosensitivity with a photo-to-dark current ratio exceeding 5 orders. This optoelectronic properties of the combinational printed OPTs are theoretically and experimentally studied, and found the comparable tendency. In addition, excellent mechanical stability is observed with up to 0.5% of strain applied to the OPTs. Hence, by manufactured with a combination of various graphic art printing methods such as roll-to-plate ROP, inkjet printing, and bar coating, these devices are very promising candidates for large-area and low-cost printed and flexible optoelectronics applications.     

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.     

Programmable logic circuits for functional integrated smart plastic systems

In this paper, we present a functional integrated plastic system. We have fabricated arrays of organic thin-film transistors (OTFTs) and printed electronic components driving an electrophoretic ink display up to 70 mm by 70 mm on a single flexible transparent plastic foil. Transistor arrays were quickly and reliably configured for different logic functions by an additional process step of inkjet printing conductive silver wires and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) resistors between transistors or between logic blocks. Among the circuit functions and features demonstrated on the arrays are a 7-stage ring oscillator, a D-type flip-flop memory element, a 2:4 demultiplexer, a programmable array logic device (PAL), and printed wires and resistors. Touch input sensors were also printed, thus only external batteries were required for a complete electronic subsystem. The PAL featured 8 inputs, 8 outputs, 32 product terms, and had 1260 p-type polymer transistors in a 3-metal process using diode-load logic. To the best of our knowledge, this is the first time that a PAL concept with organic transistors has been demonstrated, and also the first time that organic transistors have been used as the control logic for a flexible display which have both been integrated on to a single plastic substrate. The versatility afforded by the additive inkjet printing process is well suited to organic programmable logic on plastic substrates, in effect, making flexible organic electronics more flexible.     

Direct Ink‐Jet Printing of Ag–Cu Nanoparticle and Ag‐Precursor Based Electrodes for OFET Applications

The field of organic electronics has seen tremendous progress over the last years and all‐solution‐based processes are believed to be one of the key routes to ultra low‐cost roll‐to‐roll device and circuit fabrication. In this regard a variety of functional materials has been successfully designed for inkjet printing. While orthogonal‐solvent approaches have frequently been used to tackle the solubility issue in multilayer solution processing, the focus of this work lies on printed metal electrodes for organic field‐effect transistors (OFET) and their curing concepts. Two metallic inkjet‐printable materials are studied: i) a silver‐copper nanoparticle based dispersion and ii) a soluble organic silver‐precursor. Photoelectron spectroscopy reveals largely metallic properties of the cured materials, which are compared with respect to OFET performance and process‐related issues. Contact resistance of the prepared metal electrodes is significantly larger than that of evaporated top‐contact gold electrodes. As direct patterning via inkjet printing limits the reliably achievable channel length to values well above 10 μm, the influence of contact resistance is rather small, however, and overall device performance is comparable.     

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.     

Conjugated polyelectrolyte-assisted vacuum-free transfer-printing of silver nanowire network for top electrode of polymer light-emitting diodes

We report vacuum-free transfer-printing of silver nanowire (AgNW) network film as a top electrode of polymer light-emitting diodes (PLEDs) using conjugated polyelectrolyte (CPE) interfacial layer. AgNW network is delivered from a donor substrate to the desired area of the devices through an elastomeric polydimethylsiloxane (PDMS) mold stamp. The application of CPE layer with an appropriate thickness on the surface of AgNW and light-emitting polymer (LEP) films provides not only good adhesion between the organic and metal layers but also lowering of the work-function of AgNW electrode for better electron injection at LEP/AgNW interface. PLEDs with laminated AgNW top electrode at the optimized condition show the maximum device efficiencies of 3.81 cd A⁻¹ and 2.99 lm W⁻¹ at 4 V, which are comparable to those of PLEDs with Al cathode.     

Inkjet printed copper source/drain metallization for amorphoussilicon thin-film transistors

Source/drain metallization to amorphous silicon thin-film transistors has been made by inkjet printing. Contact pads of a metal organic copper precursor were inkjet printed, and then converted to copper metal at a maximum process temperature of 200°C. The copper contacts were used as the mask for back-channel etch. Laser printed toner was used for all other mask levels in a photoresist-free fabrication process. The inkjet printing of copper contacts represents a further step toward an all-printed thin-film transistor technology     

High-resolution direct-writing of metallic electrodes on flexible substrates for high performance organic field effect transistors

We report on organic field-effect transistors (OFETs) with sub-micrometer channels fabricated on plastic substrates with fully direct-written electrical contacts. In order to pattern source and drain electrodes with high resolution and reliability, we adopted a combination of two digital, direct writing techniques: ink-jet printing and femtosecond laser ablation. First silver lines are deposited by inkjet printing and sintered at low temperature and then sub-micrometer channels are produced by highly selective femtosecond laser ablation, strongly improving the lateral patterning resolution achievable with inkjet printing only. These direct-written electrodes are adopted in top gate OFETs, based on high-mobility holes and electrons transporting semiconductors, with field-effect mobilities up to 0.2 cm²/V s. Arrays of tens of devices have been fabricated with high process yield and good uniformity, demonstrating the robustness of the proposed direct-writing approach for the patterning of downscaled electrodes for high performance OFETs, compatibly with cost-effective manufacturing of large-area circuits.     

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).     

All-inkjet-printed dissolved oxygen sensors on flexible plastic substrates

Inkjet printing is a promising alternative manufacturing method to conventional standard microfabrication techniques for the development of flexible and low-cost devices. Although the use of inkjet printing for the deposition of selected materials for the development of sensor devices has been reported many times in literature, it is still a challenge and a potential route towards commercialization to completely manufacture sensor devices with inkjet technology. In this work is demonstrated the fabrication of a functional low-cost dissolved oxygen (DO) amperometric sensor with feature sizes in the micrometer range using inkjet printing. All the required technological steps for the fabrication of a complete electrochemical three electrodes system are discussed in detail. The working and counter electrodes have been printed using a gold nanoparticle ink, whereas a silver nanoparticle ink was used to print a pseudo-reference electrode. Both inks are commercially available and can be sintered at low temperatures, starting already at 120 °C, which allows the use of plastic substrates. In addition, a printable SU8 ink formulation cured by UV is applied as passivation layer in the sensor device. Finally, as the performance of analytical methods strongly depends on the working electrode material, is demonstrated the electrochemical feasibility of this printed DO sensor, which shows a linear response in the range between 0 and 8 mg L⁻¹ of DO, and affords a detection limit of 0.11 mg L⁻¹, and a sensitivity of 0.03 μA L mg⁻¹. The use of flexible plastic substrates and biocompatible inks, and the rapid prototyping and low-cost of the fabricated sensors, makes that the proposed manufacturing approach opens new opportunities in the field of biological and medical sensor applications.     

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。     

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.