Technology-based industries are constantly seeking materials and methods to fabricate compact, high-performance, and increasingly more complex printed electronic devices, fostering research in advanced conductive inks and processing techniques. Metal–organic decomposition (MOD) inks are a class of conductive inks based on molecular metal precursors that decompose into metallic features once printed, imparting them with unique attributes that distinguish them from particle-based inks. This Spotlight on Applications summarizes recent progress in understanding the chemistry, rheology, and printability of MOD inks that enable them to be printed, processed, and used with material substrates in unconventional ways. Their unique properties and capabilities are being leveraged to advance the field of printed electronics, from their use in 2.5D and 3D surfaces, wearables, and fine line printing and thus broadening the form factors and improving properties of devices used in the medial, automotive and aerospace industries.
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In the world of consumer electronics, flexible and wearable electronic devices have witnessed a remarkable transformation, and flexible supercapacitors (SCs) hold tremendous potential as a power source for these electronic devices. Printing technologies, such as inkjet and screen printing, have emerged as cost-effective and scalable manufacturing techniques for the fabrication of flexible SC electrodes. As a key element of printing technology, ink must have the right balance of conductivity and rheological properties to fabricate high-performance flexible electrodes. Graphene stands out as a promising active pigment for conductive ink due to its remarkable characteristics such as high surface area, excellent electrical conductivity, and mechanical properties. Recently, extensive research has been conducted on the development of graphene-based inks for their effective utilization in SC printing methods. This review summarizes these advances and systematically connects the graphene ink formulation with its rheological properties and correlates finally with the electrochemical performance of inkjet- and screen-printed SC electrodes.
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To meet future demands for sustainable and environmentally friendly technology, many research groups are focusing on triboelectric nanogenerators (TENGs), which can scavenge and convert the available mechanical energy into electrical energy. Researchers are working to comprehend the influence of triboelectric material surfaces as well as the properties that play an important role in determining the overall output performance of TENGs. The selection of tribonegative and tribopositive materials based on the charge in triboseries and different processes for manufacturing the triboactive material and its surface modification play important roles in attaining optimal TENG performance. The most significant tribonegative material is polyvinylidene fluoride (PVDF), and its electroactive polar β-crystalline phase is responsible for higher TENG performance. However, PVDF has some intrinsic limitations such as lower electrical conductivity and dipole moment and nonpolar α-crystalline phase at room temperature. Interestingly, these are the main factors that determine the output performance of TENG applications in energy harvesting and wearable sensors. In this review, we have mainly focused on the influence of varying processing methods like solution casting, 3-D printing, spin coating, and electrospinning on the output performance of PVDF-based TENGs. The effect of nanoscale materials on the PVDF crystalline phase is also studied in detail. Additionally, an extensive analysis of recent advancements in health monitoring, wearable sensors, and energy harvesting applications of PVDF-based TENGs is included.
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In the world of consumer electronics, flexible and wearable electronic devices have witnessed a remarkable transformation, and flexible supercapacitors (SCs) hold tremendous potential as a power source for these electronic devices. Printing technologies, such as inkjet and screen printing, have emerged as cost-effective and scalable manufacturing techniques for the fabrication of flexible SC electrodes. As a key element of printing technology, ink must have the right balance of conductivity and rheological properties to fabricate high-performance flexible electrodes. Graphene stands out as a promising active pigment for conductive ink due to its remarkable characteristics such as high surface area, excellent electrical conductivity, and mechanical properties. Recently, extensive research has been conducted on the development of graphene-based inks for their effective utilization in SC printing methods. This review summarizes these advances and systematically connects the graphene ink formulation with its rheological properties and correlates finally with the electrochemical performance of inkjet- and screen-printed SC electrodes.
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Flexible thin films of mixed ion–electron conductor Ag2Se are an attractive candidate for wearable thermoelectric applications near room temperature. In this work, deposition of Se/Ag2Se1−δ bi-layers by simple thermal evaporation followed by annealing enhances the Se content in the Ag2Se1−δ films. The Se enrichment of the Ag2Se1−δ films resulted in the improvement of the power factor through improved texturing and an enhanced Seebeck coefficient due to reduced carrier concentration. Films with Se/Ag ratio of ∼0.5 showed the highest power factor of ∼22 μW cm–1 K–2 at 320 K, i.e., 85% higher than that of films with Se/Ag ratio of 0.33. These high-performance films exhibited a very mild reversible change in the Seebeck coefficient and resistance on convex bending. A thermoelectric generator with 10 uni-legs of optimized films showed an outstanding power density of 2.6 W m–2 at a temperature difference of 10 K.
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Skyrmion-based devices have been proposed as a promising solution for low-energy data storage. These devices include racetrack or logic structures and require skyrmions to be confined in regions with dimensions comparable to the size of a single skyrmion. Here we examine skyrmions in FeGe device shapes using Lorentz transmission electron microscopy to reveal the consequences of skyrmion confinement in a device-like structure. Dumbbell-shaped elements were created by focused ion beam milling to provide regions where single skyrmions are confined adjacent to areas containing a skyrmion lattice. Simple block shapes of equivalent dimensions were also prepared to allow a direct comparison with skyrmion formation in a less complex, yet still confined, device geometry. The impact of applying a magnetic field and varying the temperature on the formation of skyrmions within the shapes was examined. This revealed that it is not just confinement within a small device structure that controls the position and number of skyrmions but that a complex device geometry changes the skyrmion behavior, including allowing skyrmions to form at lower applied magnetic fields than in simple shapes. The impact of edges in complex shapes is observed to be significant in changing the behavior of the magnetic textures formed. This could allow methods to be developed to control both the position and number of skyrmions within device structures.
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The demand for noninvasive wearable sensors for on-site monitoring has surged, particularly in the realm of personalized healthcare. This study introduces a pioneering approach employing a MXene-integrated single-stranded carbon yarn-based sensor patch utilizing a minimalist three-thread electrode setup for real-time monitoring of dopamine levels from artificial human sweat. The ability to immediately sew, weave, or stitch sensor platforms onto any type of clothing makes wearable thread-based sensor patches extremely promising, and it can be positioned in close proximity to the skin. Flexible conductive carbon yarn (CCY) was modified by Ti3C2Tx MXene by a facile dip-coating method which was used as sensing electrodes. Leveraging MXene’s high surface area and exceptional conductivity, the sensor’s architecture achieved heightened sensitivity and selectivity in dopamine detection and reproducibility in a broad linear range of 1 nM–1 μM with a detection limit of 316 pM, along with real sample tests showing the promise of this platform for real-time physiological monitoring of human performance/fitness under stress as well as diagnostic monitoring through sweat analysis. The three-thread electrode configuration, strategically embedded within the patch, ensures ease of use and comfortable, noninvasive on-body application, offering a promising avenue for continuous, real-time monitoring of dopamine levels in individuals with neurological disorders or relevant medical conditions. This study highlights the potential of MXene-integrated wearable sensor patches with a minimalist electrode setup, advancing the field of wearable sensing technologies for personalized healthcare and point-of-care diagnostics.
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The limitations of Moore’s law and the von Neumann bottleneck have sparked an increasing interest in advanced intelligent systems, such as memristors and neuromorphic devices. This work unveils the role of slow ion migration for resistive switching (RS) and exceptional environmental and mechanical resilience achieved with butane-1,4-diammonium (BDA)-based BDAPbI4 memristors, meticulously fabricated and measured in ambient conditions. These memristors demonstrate exceptional durability with consistent characteristics for up to 60 days and a slight decay in the ON/OFF ratio on the 140th day. Devices show the potential for flexible random-access memories with a low operating voltage of ∼100 mV and strong data retention and endurance measured up to 35 h and ∼1000 cycles, respectively. RS in these devices is attributed to energy barrier modulation at the perovskite/Ag interface and ion migration in the perovskite film. Furthermore, the initial investigations into their synaptic characteristics reveal stable learning behavior (potentiation and depression) and an invariant paired pulse facilitation (PPF), tested on flat and 5 mm bending radii. Additionally, the application of the spike time-dependent plasticity (STDP) Hebbian learning rule effectively demonstrates the feasibility of these memristors for neuromorphic computing applications. This is particularly promising for use in extreme mechanical conditions, such as electronic skins, and extends their potential beyond traditional data storage solutions.
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