The Internet of Things (IoT) has revolutionized the requirements for sensors and smart devices, where high performance, power efficiency and low manufacturing costs are mandatory. As a consequence, the research for better performing materials and more cost-effective manufacturing techniques is being performed. This work reports on ink formulations based on nitrogen-doped graphene and environmentally friendly polymers (Polyvinylpyrrolidone (PVP) and Carboxymethyl cellulose (CMC), and their use in fully screen-printed transistors and humidity sensors. The ink formulations were developed using environmentally friendly solvents and showed non-Newtonian behaviour. The N-rGO composites showed a high electrical conductivity of 1.9 ± 0.5 S∙cm−1, 100 times higher than the reduced graphene oxide (rGO) composites. Fully printed Graphene field effect transistors (GFET) were developed with low operating voltage of < 2 V to be implemented as humidity sensors with the fully a linear response and high sensitivity (4.25 Ω∙%RH−1 as resistive sensor), allowing integration into low-power microcontrollers for sensing applications

With the advancement of printing techniques, material choices, and ink development, high-performance printed electrochemical components relying on organic conducting polymers are beginning to mature and find traction in numerous applications in different areas, such as organic electrochromic displays (OECDs) and logic circuits based on organic electrochemical transistors (OECTs). However, the inherent hygroscopic nature of various materials in the devices, combined with electrochemically dictated working mechanisms, makes the devices sensitive to environmental changes, such as relative humidity (RH) levels and temperature (T). To ensure reliable operation of the devices, there is a need to mitigate the influence of ambience. In this article, we use commercially available printable adhesives and plastic substrates with predeposited barrier coatings to provide device encapsulation. The developed process allows for tight and conformal sealing along the topography of printed conductors reaching out from the encapsulated devices, thereby blocking the most probable leakage path. Consequently, the device performance with respect to environmental fluctuations is maintained, and the best barrier materials ensure that the performances of screen-printed OECDs and OECTs remain intact after storage in harsh conditions, such as the combination of low RH and low T or high RH and high T. Satisfactory results are achieved after a storage time of 1 week in each condition; 10% RH and 10 °C, 80% RH and 20 °C, and 90% RH and 40 °C. Additional tests performed for even longer storage times and harsh conditions, 90% RH and 40 °C, and extremely dry environment (<3% RH and 20 °C), respectively, showed devices with excellent switching performances upon evaluation. It was also discovered that the color retention of OECDs switched to their colored state, after 1 week of storage in open-circuit mode at different environmental conditions, was considerably improved upon encapsulation with barrier films.

Combining UV radiation with vapor phase polymerization (VPP) enables the fabrication of conducting polymer films with tunable electrical, optical, and electrochemical properties. However, traditional mask-based UV exposure typically requires separation between a photomask and the sample, which limits resolution. This study circumvents this by using a maskless UV exposure system that directly projects high-resolution patterns onto the substrate. Using poly(3,4-ethylenedioxythiophene):toluenesulfonate (PEDOT:Tos) as a model material, the resulting minimum feature sizes are approximately 8 µm—nearly half of what has been achieved using mask-based systems. We find that the obtained resolution is not limited by the optics but is related to material aspects such as molecular diffusion, providing guidelines for further optimizations. Our findings also show that the total delivered dose, rather than exposure time or irradiance, controls the film properties. The resulting PEDOT:Tos patterns exhibit distinct, stable color variations during electrochemical switching, highlighting the potential of maskless UV-VPP for high-resolution electrochromic displays.

Organic electrochemical transistors (OECTs) combine electron/ionic transport with organic semiconductor flexibility to connect biology and electronics. As they approach industrial use, optimizing performance requires accurate modeling of their structure. This study presents a two-dimensional (2D) OECT model based on Nernst–Planck–Poisson equations that explicitly includes volumetric capacitance (C<inf>V</inf>). Unlike previous models that ignore C<inf>V</inf>, our model highlights its essential role in OECT operation, allowing us to accurately match the measured output currents of PEDOT:PSS printed OECTs. We studied how parameters like diffusion coefficients of holes and ions, fixed anion concentration, and intrinsic capacitance affect transistor performance. We analyze existing OECT models, noting that different frameworks, despite varying assumptions, can reproduce data. This question relies solely on experimental agreement for validation. We argue that models should also be evaluated on their physical principles. To assist readers, we provide COMSOL.mph files for 1D and 2D OECT models for device design and optimization.

Recent years have shown many advances in the development of tunable structural colors by combining nanostructures with electrochromic materials. One main goal is to develop energy saving color displays that rely on ambient light instead of being emissive. However, all displays need to be pixelated to show arbitrary images and few studies have addressed the challenge of preparing and controlling individual electrochromic pixels. Herein, a very simple method to reach this milestone by using passive matrix addressing is presented, which requires no additional electronic components in the pixels. It is shown that the common transparent conductor indium tin oxide (ITO) in non-aqueous electrolytes exhibits the diode-like behavior (threshold in voltage in relation to current and coloration) necessary to prevent significant cross-talk between pixels. The chemical nature of the redox activity that enables this behavior is attributed to omnipresent oxygen and the formation of superoxide ions. Additionally, it is shown that a gel-like electrolyte can be prepared by optical lithography, which makes the concept compatible with patterning of pixels at high resolution. This method for preparing pixelated displays should be compatible with practically any type of electrochromic surface in both reflective and transmissive configurations. Also, the counter electrode maintains excellent transparency since it simply consists of ITO. The results should prove very useful as the research field of tunable structural colors moves from proof-of-concept to real devices. © 2024 Wiley-VCH GmbH.

This work demonstrates sensitive and low-cost piezoelectric sensors on skin-friendly, ultrathin, and conformable substrates combined with organic electrochemical transistors (OECTs) for the detection and amplification of alternating low-voltage input signals. The fully screen-printed (SP) piezoelectric sensors were manufactured on commercially available tattoo paper substrates, while the all-printed OECTs, relying on an extended gate electrode architecture, were manufactured either by solely using SP or by combining SP and aerosol jet printing (AJP) on PET substrates. Applying a low-voltage signal (±25 mV) to the gate electrode of the SP+AJP OECT results in approximately five times higher current modulation as compared to the fully SP reference OECT. The tattoo paper-based substrate enables transfer of the SP piezoelectric sensor to the skin, which in turn allows for radial pulse monitoring when combined with the SP+AJP OECT; this is possible due to the ability of the conformable sensor to convert mechanical vibrations into voltage signals along with the highly sensitive current modulation ability of the transistor device to further amplify the output signal. The results reported herein pave the way toward all-printed fully conformable wearable devices with high sensitivity to be further utilized for the real-time monitoring of electrophysiological signals.

Abstract This study reports on the first all-printed vertically stacked organic electrochemical transistors (OECTs) operating in accumulation mode; the devices, relying on poly([4,4?-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-2,2?-bithiophen-5,5?-diyl]-alt-[thieno[3,2-b]thiophene-2,5-diyl]) (pgBTTT) as the active channel material, are fabricated via a combination of screen and inkjet printing technologies. The resulting OECTs (W/L ≈5) demonstrate good switching performance; gm, norm ≈13 mS cm?1, µC* ≈21 F cm?1 V?1 s?1, ON?OFF ratio > 104 and good cycling stability upon continuous operation for 2 h. The inkjet printing process of pgBTTT is established by first solubilizing the polymer in dihydrolevoglucosenone (Cyrene), a non-toxic, cellulose-derived, and biodegradable solvent. The resulting ink formulations exhibit good jettability, thereby providing reproducible and stable p-type accumulation mode all-printed OECTs with high performance. Besides the environmental and safety benefits of this solvent, this study also demonstrates the assessment of how the solvent affects the performance of spin-coated OECTs, which justifies the choice of Cyrene as an alternative to commonly used harmful solvents such as chloroform, also from a device perspective. Hence, this approach shows a new possibility of obtaining more sustainable printed electronic devices, which will eventually result in all-printed OECT-based logic circuits operating in complementary mode.

Displays are one of the most mature technologies in the field of printed electronics. Their ability to be manufactured in large quantities and at low cost has led to their recent uptake into the consumer market. Within this article this technology is extended to electrochromic display stickers. This is achieved using a recent reverse display architecture screen printed on textile and paper sticker substrates. The electrochromic stickers are comparable to plastic control substrates and show little performance difference even when adhered to curved surfaces. The electrochromic display technology is extended to sticker labels for authentication applications by patterning either the dielectric or the graphical layer. A proof-of-concept prototype emulating a wax seal on an envelope is presented to show that other colors can be implemented in this technology. © 2023 The Authors.

Low-cost, flexible and thin display technology is becoming an interesting field of research as it can accompany the wide range of sensors being developed. Here, the synthesis of poly(dimethylpropylene-dioxythiophene) (PProDOT-Me2) by combining vapor phase polymerization and screen printing is presented. A multilayer architecture using poly(3,4-ethylenedioxythiophene) (PEDOT) and PProDOT-Me2 to allow for electrochromic switching of PProDOT-Me2, thereby eliminating the need for a supporting transparent conductive (metal oxide) layer is introduced. Furthermore, the technology is adapted to a blended architecture, which removes the additional processing steps and results in improved color contrast (∆E* &gt; 25). This blend architecture is extended to other conductive polymers, such as PEDOT and polypyrrole (PPy), to highlight the ability of the technique to adjust the color of all-printed electrochromic displays. As a result, a green color is obtained when combining the blue and yellow states of PEDOT and PPy, respectively. This technology has the potential to pave the way for all-printed multicolored electrochromic displays for further utilization in printed electronic systems in various Internet of Things applications. © 2022 The Authors. 

Manufacturing of electronic devices via printing techniques is often considered to be an environmentally friendly approach, partially due to the efficient utilization of materials. Traditionally, printed electronic components (e.g., sensors, transistors, and displays) are relying on flexible substrates based on plastic materials; this is especially true in electronic display applications where, most of the times, a transparent carrier is required in order to enable presentation of the display content. However, plastic-based substrates are often ruled out in end user scenarios striving toward sustainability. Paper substrates based on ordinary cellulose fibers can potentially replace plastic substrates, but the opaqueness limits the range of applications where they can be used. Herein, electrochromic displays that are manufactured, via screen printing, directly on state-of-the-art fully transparent substrates based on nanocellulose are presented. Several different nanocellulose-based substrates, based on either nanofibrillated or nanocrystalline cellulose, are manufactured and evaluated as substrates for the manufacturing of electrochromic displays, and the optical and electrical switching performances of the resulting display devices are reported and compared. The reported devices do not require the use of metals and/or transparent conductive oxides, thereby providing a sustainable all-printed electrochromic display technology.