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).     

Fully printed electronics on flexible substrates: High gain amplifiers and DAC

We propose a novel simple Fully-Additive printing process, involving only depositions, for realizing printed electronics circuits/systems on flexible plastic films. This process is Green (non-corrosive chemicals), On-Demand (quick-to-print), Scalable (large-format printing) and Low-Cost vis-à-vis Subtractive printing, a complex deposition-cum-etching process that otherwise requires expensive/sophisticated specialized IC-like facilities and is Un-Green, Not-On-Demand, Un-scalable and High-Cost. The proposed Fully-Additive process features printed transistors with high (∼1.5 cm²/Vs) semiconductor carrier-mobility, ∼3× higher than competing state-of-the-art Fully-Additive processes and comparable to Subtractive processes. Furthermore, passive elements including capacitors, resistors, and inductors, and two metal-interconnect layers are likewise Fully-Additive printed–to our knowledge, to-date the only Fully-Additive process capable of realizing complex circuits/systems on flexible plastic films.Several analog and mixed-signal circuits are demonstrated, including proposed and conventional differential amplifiers, and a charge-redistribution 4-bit digital-to-analog converter (DAC). The proposed amplifier embodies a novel positive-cum-negative feedback to simultaneously significantly improve the gain and reduce susceptibility to process variations. To improve the speed and reduce the area of the DAC, the parasitic capacitors therein are exploited. The Fully-Additive proposed amplifier and DAC are benchmarked against reported realizations (all Subtractive-based processes), and are shown to be highly competitive despite its realization based on the simple low-cost proposed Fully-Additive process.     

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.     

Printable and Flexible Phototransistors Based on Blend of Organic Semiconductor and Biopolymer

Printable and flexible organic phototransistors (OPTs) make comprehensive requirements for the organic semiconductors (OSCs), including high photosensitivity, decent transistor characteristics, appropriate solution viscosity, and good film flexibility. It has been challenging to obtain such semiconductors. Here, we demonstrated that by taking advantage of the interfacial charge effect, printable and flexible OPTs with high performance can be successfully fabricated through simply blending common OSCs with polymers. Using 2,7‐dioctyl[1]benzothieno[3,2‐b][1]benzothiophene and an insulating biopolymer polylactide, OPTs with blended and layered structure are both fabricated and investigated. The photoresponses of the OPTs can be modulated by gate voltage over 1000 times, and their responsivities are measured up to 400 A W^?1. As compared to the layered OPTs, the blended ones exhibit higher photocurrent to dark current ratio (up to 10⁵) and better light detection limit (lower than 0.02 mW cm^?2). The improvements are attributed to larger interfacial area and more intensive charge trapping effect. The flexible OPTs are further fabricated by inkjet printing the blended solution. This work presents OPTs with comprehensive advantages including low cost, enhanced photosensitivity, great flexibility, and printability, which are realized by simply blending common OSC with polymer, and thus provide an inspiration for the design of novel organic electronics.     

Microcapacitors with controlled electrical capacity in the pF–nF range printed by laser-induced forward transfer (LIFT)

Micrometric-sized pixels of hybrid organic–inorganic thin films (Ag/parylene-C) have been printed by laser-induced forward transfer (LIFT) on flexible, cost-efficient substrates. Micrometric capacitors have been fabricated by laser printing such pixels together with silver nanoparticles (AgNP) paste. The AgNP paste has been deposited in the shape of square pads, acting as bottom electrode. This combination is suitable to be used in microelectronic circuits, as the electrical components exhibit controllable capacity in the pF–nF range. Electrical characterizations of the printed pixels demonstrate that the capacitors are fully operative and stable over time.     

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.     

All ink-jet printed low-voltage organic field-effect transistors on flexible substrate

In this work, all ink-jet printed (IJP) low-voltage organic field-effect transistors (OFETs) on flexible substrate are reported. The OFETs use IJP silver (Ag) for source/drain/gate electrodes, poly(4-vinylphenol) (PVP) for gate dielectric, 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) blended with polystyrene (PS) as the semiconducting layer and CYTOP for encapsulation layer. All the printing processes were carried out in ambient air environment using a single laboratory ink-jet printer Dimatix DMP-2831. The all IJP device presents state-of-the-art performance with low operation voltage down to 3 V, small subthreshold swing (SS) of 0.155 V/decade, mobility of 0.26 cm² V⁻¹s⁻¹, threshold voltage (V_th) of −0.17 V and on/off ratio of 3.1 × 10⁵, along with a yield of 62.5%. Through interface engineering and proper process optimization, this work demonstrates a promising low-voltage all IJP device platform for low-cost flexible printed electronics.     

Printing-induced improvements of organic thin-film transistors

To understand the observation of improved pentacene (Pn) thin-film transistor mobility in flexible printed devices, a method for performing electrical measurements of organic thin-film transistors (OTFT) during the process of transfer printing has been developed. Different sample configurations were designed to test two aspects of the printing process: (1) the formation of the source/drain contacts a Pn thin-film, and (2) the formation of the transfer printed Pn/dielectric interface. In situ measurements show that pressure-induced contacts of gold (Au) electrodes result in a factor of seven mobility improvement compared with evaporation of top Au electrodes on an otherwise identical device configuration. Annealing the laminated device up to 90 °C caused no further improvement, and heating above 90 °C degraded performance. The mobility of a transfer printed device with the rough, as-grown top surface of the Pn in contact with the dielectric was found to increase dramatically with subsequent annealing for a sample temperature up to 120 °C. This is attributed to annealing-induced structural changes in the Pn film at elevated temperatures, consistent with X-ray bulk measurements showing enhanced crystal morphology in transfer printed Pn thin-films.     

Tuning domain size and crystallinity in isoindigo/PCBM organic solar cells via solution shearing

Despite having achieved the long sought-after performance of 10% power conversion efficiency, high performance organic photovoltaics (OPVs) are still mostly constrained to lab scale devices fabricated by spin coating. Efforts to produce printed OPVs lag considerably behind, and the sensitivity to different fabrication methods highlights the need to develop a comprehensive understanding of the processing-morphology relationship in printing methods. Here we present a systematic experimental investigation of a model low bandgap polymer/fullerene system, poly-isoindigo thienothiophene/PC₆₁BM, using a lab-scale analogue to roll-to-roll coating as the fabrication tool in order to understand the impact of processing parameters on morphological evolution. We report that domain size and polymer crystallinity can be tuned by a factor of two by controlling the temperature and coating speed. Lower fabrication temperature simultaneously decreased the phase separation domain size and increased the relative degree of crystallinity in those domains, leading to improved photocurrent. We conclude that domain size in isoindigo/PCBM is dictated by spontaneous phase separation rather than crystal nucleation and growth. Furthermore we present a model to describe the temperature dependence of domain size formation in our system, which demonstrates that morphology is not necessarily strictly dependent on the evaporation rate, but rather on the interplay between evaporation and diffusion during the printing process.     

Inkjet Printed Large‐Area Flexible Few‐Layer Graphene Thermoelectrics

Graphene‐based organic nanocomposites have ascended as promising candidates for thermoelectric energy conversion. In order to adopt existing scalable printing methods for developing thermostable graphene‐based thermoelectric devices, optimization of both the material ink and the thermoelectric properties of the resulting films are required. Here, inkjet‐printed large‐area flexible graphene thin films with outstanding thermoelectric properties are reported. The thermal and electronic transport properties of the films reveal the so‐called phonon‐glass electron‐crystal character (i.e., electrical transport behavior akin to that of few‐layer graphene flakes with quenched thermal transport arising from the disordered nanoporous structure). As a result, the all‐graphene films show a room‐temperature thermoelectric power factor of 18.7 µW m^?1 K^?2, representing over a threefold improvement to previous solution‐processed all‐graphene structures. The demonstration of inkjet‐printed thermoelectric devices underscores the potential for future flexible, scalable, and low‐cost thermoelectric applications, such as harvesting energy from body heat in wearable applications.     

3D Printing of Hydrogels for Stretchable Ionotronic Devices

In the booming development of flexible electronics represented by electronic skins, soft robots, and human–machine interfaces, 3D printing of hydrogels, an approach used by the biofabrication community, is drawing attention from researchers working on hydrogel-based stretchable ionotronic devices. Such devices can greatly benefit from the excellent patterning capability of 3D printing in three dimensions, as well as the free design complexity and easy upscale potential. Compared to the advanced stage of 3D bioprinting, 3D printing of hydrogel ionotronic devices is in its infancy due to the difficulty in balancing printability, ionic conductivity, shape fidelity, stretchability, and other functionalities. In this review, a guideline is provided on how to utilize the power of 3D printing in building high-performance hydrogel-based stretchable ionotronic devices mainly from a materials’ point of view, highlighting the systematic approach to balancing the printability, printing quality, and performance of printed devices. Various 3D printing methods for hydrogels are introduced, and then the ink design principles, balancing printing quality, printed functions, such as elastic conductivity, self-healing ability, and device (e.g., flexible sensors, shape-morphing actuators, soft robots, electroluminescent devices, and electrochemical biosensors) performances are discussed. In conclusion, perspectives on the future directions of this exciting field are presented.     

Blade Coating of Alloy as Top Electrodes for Efficient All-Printed Organic Photovoltaics

All printing of organic photovoltaics (OPVs) including the top electrode is highly desirable for achieving cost-effective, high-throughput, and large-area photovoltaic manufacturing. Here, the printing of a low-melting-point alloy as top electrodes in OPVs via blade coating is investigated. The Field's metal (FM) with the melting point of 62 °C is adopted for the top electrodes, because FM can be printed under moderate temperatures without harming the active layers while remaining solid state under solar irradiation. The correlations between the processing parameters and properties of the blade-coated electrodes are elucidated. OPVs based on the D18:Y6 active layer and blade-coated FM electrodes achieve a highest power conversion efficiency of 17.28%. The OPVs with FM-electrode demonstrate much higher thermal stability than that of the Ag-electrode devices. All-printed OPVs, in which the FM electrode is blade coated and the other layers are prepared by flexible micro-comb printing, exhibit an efficiency of 16.07%. The results represent the records of evaporation-free and all-printed OPVs, demonstrating that printing FM as OPV electrodes is a cost-effective and time-saving strategy to substitute the vacuum-evaporated metals, as well as a feasible route toward high-performance all-printed OPVs.     

Low-voltage organic phototransistors based on naphthyl end-capped oligothiophene nanofibers

Organic crystalline semiconductors with highly ordered molecular packing could be vital components in novel low power consumption light sensors due to their unique light absorption and charge carrier transport properties. In this work, we show that nanofibers made from naphthyl end-capped bithiophenes can be used for low-voltage, high responsivity organic phototransistors (OPTs). Density functional theory (DFT) calculations have been carried out to estimate the device properties related to charge transport and photon absorption. In terms of the calculation of the reorganization energy upon charge transfer, we used an extended method to include inter-molecule interactions. Experimentally, the device performance of the 5,5-bis(naphthyl)-2,2′-bithiophene (NaT2) nanofiber OPTs has been compared with that of a thin film OPT with inferior molecular ordering. The better photoresponsivity of the nanofiber OPT compared with the thin film OPT under monochromatic illumination at various wavelengths suggests that the NaT2 nanofiber-based OPTs have great potential to be used as high performance nano-scale light detectors. Moreover, the absorption of the nanofiber-based OPTs is also polarization sensitive, which provides another advantage of nanofiber-based devices in terms of potential novel sensor design.     

Automated fabrication of hybrid printed electronic circuits

Printed electronics offer great potential for new applications such as Internet of Things devices and wearables. However, to date, only a limited number of electronic functions and integration densities can be realised by printing processes. Hence, hybrid printed electronic circuits are actually created by mounting silicon electronic components. Since both printed materials and processes are continuously evolving, an accompanying structured development methodology is required. This paper highlights a digital workflow from design to automated fabrication using the example of a demonstrator circuit. A multi-layer vector ink-jet printing process to print electronic devices onto foil substrates with three functional inks is presented. This printing process is improved using a newly set-up printing system: Integrating a piezo print head into the path planning of the printing system and its control as a virtual stepper axis enable highly precise vector printing. This leads to printed resistors with low tolerances. Adaptations of surface mount technology for assembling silicon electronic components onto printed foil substrates are discussed. Finally, image processing methods to cope with deformations of the flexible foil substrates in the fabrication process are introduced.     

A transition solvent strategy to print polymer:fullerene films using halogen-free solvents for solar cell applications

Inkjet printing is a mask-less non-contact deposition technique that is potentially suited for prototyping and manufacturing of thin-film polymer organic semiconductor devices from digital images. However new strategies are needed to achieve films with good macromorphology (i.e., high-fidelity footprint and uniform cross-section) and nanomorphology on unstructured substrates using a conventional ink-jet. Here we report a new transition solvent strategy to provide the desired film macromorphology and ultrafine nanomorphology in regioregular poly(3-hexylthiophene):phenyl-C₆₁-butyric acid methyl ester (P3HT:PCBM) model films, without using chlorinated solvents. This strategy employs a good volatile solvent in combination with a miscible poor solvent that is much less volatile, which is the reverse of the usual low−high boiling-point solvent method. The good solvent suppresses premature aggregation in the ink head. Its removal by evaporation on the substrate leaves the poor solvent that triggers early π-stacking ordering and/or gelation of the polymer matrix that immobilizes the printed fluid on the substrate, suppressing both contact-line depinning and evaporation-induced solvent flow effects. The resultant donor–acceptor nanomorphology is further improved by vacuum drying at an optimal rate that avoids bubble formation. We have systematically characterized P3HT:PCBM films deposited with different solvents and platen temperatures to identify key macro- and nano-morphology determining processes. High-performance printed P3HT:PCBM solar cells were realized. These findings are applicable also to other printing and coating techniques based on low-viscosity inks.     

Organische Feldeffekttransistoren auf Basis halbleitender Polymere

At present a variety of companies and institutes in the world are working on the development of organic field-effect transistors (OFET) and integrated polymer circuits (IPCs) to create a new low-cost low-performance electronics. This is especially suited for low-end electronics and RFID applications like electronic labels, smart cards, ident tags, electronic bar codes etc., which are needed in large amounts at lowest prices. The transistors are made as thin film transistors on flexible or rigid substrates by successive coating with the appropriate functional materials (polymer semiconductor, insulator, layers for electrodes). This setup can be realized either by organic and polymer materials only as well as by a combination of organic with inorganic materials. All-polymer field-effect transistors (PFETs) which completely consist of polymer layers (source, drain and gate electrodes, semiconductor, insulator) are of special interest. Later on they will offer the chance to use printing techniques for their production which enables high-volume printing of electronic circuits.     

纳米压印技术的最新进展

总结了纳米压印技术的最新进展,其中包括压印工艺、图形赋形方法以及纳米压印技术应用三方面最新的研究成果。在压印工艺的发展方面,大面积滚轴压印的发明最具有产业化意义,它不仅解决了常规平板压印很难大面积压印成型的困难,而且整个过程是一种柔性压印过程,降低了成本,提高了压印效率,但是最小特征尺寸还有待提高;在图形赋形方法的改进中,聚合物探针阵列技术集微米和纳米成型技术于一身,压印效率高,应用前景广阔;在压印技术应用的发展中,光伏电池、电子存储设备以及传感器等为纳米压印技术的应用提供了新的领域。     

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.     

Roller-type gravure offset printing of conductive inks for high-resolution printing on ceramic substrates

The use of gravure offset printing methods at an industrial level requires a wide and deep knowledge of the printing properties of the inks. Novel hydrocarbon inks were developed with superior printing properties compared to alternative ethyl cellulose-based inks. There are principal behaviour properties of these inks that can be generally described. In particular, the resistance dependence of printed mass for single and multiprints and on the other hand, the effect of multiprinting on printed area smoothness and line height.

This article summarizes the results obtained and describes printing properties and defects: line widening, hair formation, ink flow from the gravure grooves, pinholes, image distortions, ribbing, scooping, streaking and gravure groove blocking. Three different printed samples were demonstrated, which are best suited for this manufacturing method: interdigital capacitor, inductor coil and laser soldering substrates.