The development of electronics with net zero carbon emissions through more efficient and environmentally friendly materials and processes is still a challenge. Here, alternative chemical synthesis routes of metal conductive nanoparticles, based on biodegradable materials are explored, such as nickel, iron–nickel alloy and iron nanoparticles, to be used, in the long term, as fillers in inks for inject printing. Thus, Ni and FeNi metal nanoparticles of 25–12 nm, forming aggregates of 614–574 nm, respectively, are synthesized in water in the presence of a polyol and a reducing agent and under microwave heating that enables a more uniform and fast heating. Iron nanoparticles of 120 ± 40 nm are synthesized in polyol that limits the aggregation and the oxidation degree. Commercial metal nanoparticles of iron and nickel, are coated with ethylene glycol and used for comparison. The conductivity of nanoparticles when pressed into pellets remains similar for both commercial and synthesized samples. However, when deposited on a strip line and heated, synthesized Ni, FeNi, and Fe nanoparticles show significant conductivity and interesting magnetic properties. It is demonstrated that the nanosize facilitates sintering at reduced temperatures and the capping agents prevent oxidation, resulting in promising conductive fillers for printed electronic applications. 

With the increasing global demand for net-zero carbon emissions, actions to address climate change have gained momentum among policymakers and the public. The urgent need for a sustainable economy is underscored by the mounting waste crisis in landfills and oceans. However, the proliferation of distributed electronic devices poses a significant challenge due to the resulting electronic waste. To combat this issue, the development of sustainable and environmentally friendly materials for these devices is imperative. Cellulose, an abundant and CO2-neutral substance with a long history of diverse applications, holds great potential. By integrating electrically interactive components with cellulosic materials, innovative biobased composites have been created, enabling the fabrication of bulk electroactive paper and the establishment of new, potentially more sustainable manufacturing processes for electronic devices. This review explores recent advances in bulk electroactive paper, including the fundamental interactions between its constituents, manufacturing techniques, and large-scale applications in the field of electronics. Furthermore, it addresses the importance and challenges of scaling up production of electroactive paper, highlighting the need for further research and development.

Hydrogels are of great importance for functionalizing sensors and microfluidics, and poly(ethylene glycol) dimethacrylate (PEG-DMA) is often used as a viscosifier for printable hydrogel precursor inks. In this study, 1–10 kDa PEG-DMA based hydrogels were characterized by gravimetric and electrochemical methods to investigate the diffusivity of small molecules and proteins. Swelling ratios (SRs) of 14.43–9.24, as well as mesh sizes ξ of 3.58–6.91 nm were calculated, and it was found that the SR correlates with the molar concentration of PEG-DMA in the ink (MCI) (SR = 0.1127 × MCI + 8.3256, R2 = 0.9692) and ξ correlates with the molecular weight (Mw) (ξ = 0.3382 × Mw + 3.638, R2 = 0.9451). To investigate the sensing properties, methylene blue (MB) and MB-conjugated proteins were measured on electrochemical sensors with and without hydrogel coating. It was found that on sensors with 10 kDa PEG-DMA hydrogel modification, the DPV peak currents were reduced to 92 % for MB, 73 % for MB-BSA, and 23 % for MB-IgG. To investigate the diffusion properties of MB(-conjugates) in hydrogels with 1–10 kDa PEG-DMA, diffusivity was calculated from the current equation. It was found that diffusivity increases with increasing ξ. Finally, the release of MB-BSA was detected after drying the MB-BSA-containing hydrogel, which is a promising result for the development of hydrogel-based reagent reservoirs for biosensing. 

Porous carbon materials are common materials used for sensor and absorbent applications. A novel approach for functionalizing porous carbons through the impregnation of porous carbon black with benzoxazine monomers, followed by thermal polymerization is introduced herein. The method not only establishes a new avenue for the functionalization of porous carbons but also endows the resulting material with both copper ion-binding and sensing properties. We showcase the versatility of the technique by illustrating that the polymerization of phenols with benzoxazine monomers serves as an extra tool to customize absorption- and sensing properties. Experimental validation involved testing the method on carbon black as a porous substrate, which was impregnated with both bisphenol-a benzoxazine and a combination of bisphenol-a benzoxazine and alizarin. The resulting materials were assessed for their dual functionality as both an absorbent and a sensor for copper ions by varied copper ion concentrations and exposure times. The dye absorption test demonstrated a notable capacity to accumulate copper ions from dilute solutions. Electrochemical characterization further confirmed the effectiveness of the modified carbons, as electrodes produced from inks were successful in detecting copper ions accumulated from 50 μM Cu2+ solutions. With this work, we aspire to set the steppingstone towards a facile functionalization of porous carbon materials towards water purification applications. © 2024 The Authors

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.

The transition to a sustainable society is driving the development of green electronic solutions designed to have a minimal environmental impact. One promising route to achieve this goal is to construct electronics from biobased materials like cellulose, which is carbon neutral, non‐toxic, and recyclable. This is especially true for internet‐of‐things devices, which are rapidly growing in number and are becoming embedded in every aspect of our lives. Here, paper‐based sensor circuits are demonstrated, which use triboelectric pressure sensors to help elderly people communicate with the digital world using an interface in the form of an electronic “book”, which is more intuitive to them. The sensors are manufactured by screen printing onto flexible paper substrates, using in‐house developed cellulose‐based inks with non‐hazardous solvents. The triboelectric sensor signal, generated by the contact between a finger and chemically modified cellulose, can reach several volts, which can be registered by a portable microcontroller card and transmitted by Bluetooth to any device with an internet connection. Apart from the microcontroller (which can be easily removed), the whole system can be recycled at the end of life. A triboelectric touch interface, manufactured using printed electronics on flexible paper substrates, using cellulose‐based functional inks is demonstrated. These metal‐free green electronics circuits are implemented in an “electronic book” demonstrator, equipped with wireless communication that can control remote devices, as a step toward sustainable and recyclable internet‐of‐things devices.

Novel printed electronics are projected to grow and be manufactured in the future in large volumes. In many applications, printed electronics are envisaged as sustainable alternatives to conventional (PCB-based) electronics. One such application is in the semi-quantitative drug detection and point-of-care device called ‘GREENSENSE’ that uses paper-based printed electronics. This paper analyses the carbon footprint of GREENSENSE in order to identify and suggest means of mitigating disproportionately high environmental impacts, labeled ‘sustainability hotspots’, from materials and processes used during production which would be relevant in high-volume applications. Firstly, a life cycle model traces the flow of raw materials (such as paper, CNCs, and nanosilver) through the three ‘umbrella’ processes (circuit printing, component mounting, and biofunctionalization) manufacturing different electronic components (the substrate, conductive inks, energy sources, display, etc) that are further assembled into GREENSENSE. Based on the life cycle model, life cycle inventories are modeled that map out the network of material and energy flow throughout the production of GREENSENSE. Finally, from the environmental impact and sustainability hotspot analysis, both crystalline nanocellulose and nanosilver were found to create material hotspots and they should be replaced in favor of lower-impact materials. Process hotspots are created by manual, lab-, and pilot-scale processes with unoptimized material consumption, energy use, and waste generation; automated and industrial-scale manufacturing can mitigate such process hotspots. © 2023 The Author(s).

Wood is an inherently hygroscopic material which tends to absorb moisture from its surrounding. Moisture in wood is a determining factor for the quality of wood being employed in construction, since it causes weakening, deformation, rotting, and ultimately leading to failure of the structures resulting in costs to the economy, the environment, and to the safety of residents. Therefore, monitoring moisture in wood during the construction phase and after construction is vital for the future of smart and sustainable buildings. Employing bio-based materials for the construction of electronics is one way to mitigate the environmental impact of such electronics. Herein, a bio-graphene sensor for monitoring the moisture inside and around wooden surfaces is fabricated using laser-induced graphitization of a lignin-based ink precursor. The bio-graphene sensors are used to measure humidity in the range of 10% up to 90% at 25 °C. Using laser induced graphitization, conductor resistivity of 18.6 Ω sq−1 is obtained for spruce wood and 57.1 Ω sq−1 for pine wood. The sensitivity of sensors fabricated on spruce and pine wood is 2.6 and 0.74 MΩ per % RH. Surface morphology and degree of graphitization are investigated using scanning electron microscopy, Raman spectroscopy, and thermogravimetric analysis methods. © 2023 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.