Stretchable organic electrochemical transistors (OECTs) are promising for wearable applications within biosensing, bio-signal recording, and addressing circuitry. Efficient large-scale fabrication of OECTs can be performed with printing methods but to date there are no reports on high-performance fully printed stretchable OECTs. Herein, this challenge is addressed by developing fully screen-printed stretchable OECTs based on an architecture that minimizes electrochemical side reactions and improves long-term stability. Fabrication of the OECTs is enabled by in-house development of three stretchable functional screen-printing inks and related printing processes. The stretchable OECTs show good characteristics in terms of transfer curves, output characteristics, and transient response up to 100% static strain and 500 strain cycles at 25% and 50% strain. The strain insensitivity of the OECTs can be further improved by strain conditioning, resulting in stable performance up to 50% strain. Finally, an electrochromic smart pixel is demonstrated by connecting a stretchable OECT to a stretchable electrochromic display. It is believed that the development of screen-printed stretchable electrochemical devices, and OECTs in particular, will pave the way for their use in wearable applications and commercial products. © 2023 The Authors. 

Smart label technology such as indicators is a growing field due to society's demand for Internet of Things devices. New materials and technologies are continuously being discovered and developed in order to provide better resolution, better performance, or more environmentally friendly devices. Within this report, screen printing technology is combined with vapor phase polymerization to synthesize three conductive polymers; poly(3,4-ethylenedioxythiophene) (PEDOT), polypyrrole (PPy), and polythiophene (PTh). The conductive polymers are created in micrometer resolution and investigated for their electrochromic properties. PEDOT and PPy samples are combined into printed, laminated, transmissive electrochromic displays. The technology is further advanced to establish separate PEDOT, PPy, and PTh all-printed electrochromic displays using several screen printed layers. The PEDOT displays show improved color retention as compared to displays created with commercially available PEDOT:poly(styrene sulfonate) (PSS) with comparable contrast and switching behavior. All-printed PPy and PTh electrochromic displays with impressive electrochromic behavior are demonstrated. More complex patterns of 7-segment displays are created, thereby highlighting flexibility and individually switched sections of the conductive polymers. This research extends the screen printing and vapor phase polymerization combination to other conductive polymers and the potential commercialization of multicolor electrochromic displays that has been otherwise dominated by monochromatic PEDOT:PSS. 

Large area manufacturing of printed electronic components on ~A4-sized substrates is demonstrated by the combination of screen printing and vapor phase polymerization (VPP) into poly(3,4-ethylenedioxythiophene) (PEDOT). The oxidant layer required for the polymerization process is screen printed, and the resulting conductive polymer patterns are manufactured at high resolution (100 µm). Successful processing of several common oxidant species is demonstrated, and the thickness can be adjusted by altering the polymerization time. By comparing the polymer films of this work to a commercial PEDOT:PSS (PEDOT doped with poly(styrene sulfonate)) screen printing ink shows improved surface roughness (26 vs 69 nm), higher conductivity (500 vs 100 S cm–1) and better resolution (100 vs 200 µm). Organic electrochemical transistors, in which the transistor channel is polymerized into PEDOT through VPP, are also demonstrated to further emphasize on the applicability of this manufacturing approach. The resulting transistor devices are not only functional, they also show remarkable switching behavior with respect to ON current levels (–70 mA at –1 V), ON/OFF ratios (>105), switching times (tens of ms) and transconductance values (>100 mS) in standalone transistor devices, in addition to a high amplification factor (>30) upon integration into a screen printed inverter circuit. © 2022 The Authors. 

Microfluidic surface chemistry can enable control of capillary-driven flow without the need for bulky external instrumentation. A novel pondered nonhomogeneous coating defines regions with different wetting properties on the microchannel walls. It changes the curvature of the liquid–air meniscus at various channel cross-sections and consequently leads to different capillary pressures, which is favorable in the strive toward automatic flow control. This is accomplished by the deposition of hydrophilic coatings on the surface of multilevel 3D-printed (3DP) microfluidic devices via inkjet printing, thereby retaining the surface hydrophilicity for at least 6 months of storage. To the best of our knowledge, this is the first demonstration of capillary flow control in 3DP microfluidics enabled by inkjet printing. The method is used to create “stop” and “delay” valves to enable preprogrammed capillary flow for sequential release of fluids. To demonstrate further utilization in point-of-care sensing applications, screen printed organic electrochemical transistors are integrated within the microfluidic chips to sense, sequentially and independently from external actions, chloride anions in the (1–100) × 10−3 m range. The results present a cost-effective fabrication method of compact, yet comprehensive, all-printed sensing platforms that allow fast ion detection (<60 s), including the capability of automatic delivery of multiple test solutions. © 2023 The Authors. 

This work demonstrates a novel fabrication approach based on the combination of screen and aerosol jet printing to manufacture fully printed organic electrochemical transistors (OECTs) and OECT-based logic circuits on PET substrates with superior performances. The use of aerosol jet printing allows for a reduction of the channel width to ≈15 µm and the estimated volume by a factor of ≈40, compared to the fully screen printed OECTs. Hence, the OECT devices and OECT-based logic circuits fabricated with the proposed approach emerge with a high ON/OFF ratio (103–104) and remarkably fast switching response, reaching an ON/OFF ratio of &gt;103 in 4–8 ms, which is further demonstrated by a propagation delay time of just above 1 ms in OECT-based logic inverter circuits operated at a frequency of 100 Hz. All-printed monolithically integrated OECT-based five-stage ring oscillator circuits further validated the concept with a resulting self-oscillation frequency of 60 Hz. © 2022 The Authors.

Microfluidic fiber spinning is a promising technique for assembling cellulose nanomaterials into macroscopic fibers. However, its implementation requires upscalabe fabrication processes while maintaining high strength of the fibers, which could not be previously achieved. Herein, a continuous wet spinning process based on microfluidic flow focusing is developed to produce strong fibers from cellulose nanofibrils (CNFs) and nanocrystals (CNCs). Fibers with an average breaking tenacity as high as 29.5 cN tex−1 and Young's modulus of 1146 cN tex−1 are reported for the first time, produced from nonhighly purified CNF grades. Using the same developed method, wet spinning of fibers from CNCs is achieved for the first time, reaching an average Young's modulus of 1263 cN tex−1 and a breaking tenacity of 10.6 cN tex−1, thus exhibiting strength twice as high as that of common CNC films. A rather similar stiffness of CNC and CNF spun fibers may originate from similar degrees of alignment, as confirmed by wide-angle X-ray scattering (WAXS) and birefringence measurements, whereas lower strength may primarily arise from the shorter length of CNCs compared to that of CNFs. The benefit of CNCs is their higher solids content in the dopes. By combining both CNCs and CNFs, the fiber properties can be tuned.

Ultrathin devices are rapidly developing for skin-compatible medical applications and wearable electronics. Powering skin-interfaced electronics requires thin and lightweight energy storage devices, where solution-processing enables scalable fabrication. To attain such devices, a sequential deposition is employed to achieve all spray-coated symmetric microsupercapacitors (μSCs) on ultrathin parylene C substrates, where both electrode and gel electrolyte are based on the cheap and abundant biopolymer, cellulose. The optimized spraying procedure allows an overall device thickness of ≈11 µm to be obtained with a 40% active material volume fraction and a resulting volumetric capacitance of 7 F cm−3. Long-term operation capability (90% of capacitance retention after 104 cycles) and mechanical robustness are achieved (1000 cycles, capacitance retention of 98%) under extreme bending (rolling) conditions. Finite element analysis is utilized to simulate stresses and strains in real-sized μSCs under different bending conditions. Moreover, an organic electrochromic display is printed and powered with two serially connected μ-SCs as an example of a wearable, skin-integrated, fully organic electronic application. © 2022 The Authors. 

Organic electronic circuits based on organic electrochemical transistors (OECTs) are attracting great attention due to their printability, flexibility, and low voltage operation. Inverters are the building blocks of digital logic circuits (e.g., NAND gates) and analog circuits (e.g., amplifiers). However, utilizing OECTs in electronic logic circuits is challenging due to the resulting low voltage gain and low output voltage levels. Hence, inverters capable of operating at relatively low supply voltages, yet offering high voltage gain and larger output voltage windows than the respective input voltage window are desired. Herein, inverters realized from poly(3,4-ethylenedioxythiophene):polystyrene sulfonate-based OECTs are designed and explored, resulting in logic inverters exhibiting high voltage gains, enlarged output voltage windows, and tunable switching points. The inverter designs are based on multiple screen-printed OECTs and a resistor ladder, where one OECT is the driving transistor while one or two additional OECTs are used as variable resistors in the resistor ladder. The inverters’ performances are investigated in terms of voltage gain, output voltage levels, and switching point. Inverters, operating at +/−2.5 V supply voltage and an input voltage window of 1 V, that can achieve an output voltage window with ∼110% increment and a voltage gain up to 42 are demonstrated. © 2022 The Authors.

Low-voltage operating organic electronic circuits with long-term stability characteristics are receiving increasing attention because of the growing demands for power efficient electronics in Internet of Things applications. To realize such circuits, inverters, the fundamental constituents of many circuits, with stable transfer characteristics should be designed to provide low-power consumption. Here, a rational inverter design, based on fully screen printed p-type organic electrochemical transistors with a channel size of 150 × 80 µm2, is explored for driving conditions with input voltage levels that differs of about 1 V. Further, three different inverter circuits are explored, including resistor ladders with resistor values ranging from tens of kΩ to a few MΩ. The performance of single inverters, 3-stage cascaded inverters and 3-stage ring oscillators are characterized with respect to output voltage levels, propagation delay, static power consumption, voltage gain, and operational frequency window. Depending on the application, the key performance parameters of the inverter can be optimized by the specific combination of the input voltage levels and the resistor ladder values. A few of the inverters are in fact fully functional up to 30 Hz, even when using input voltage levels as low as (0 V, 1 V). © 2021 The Authors.