Solution-Processed Flexible Transparent Electrodes for Printable Electronics

Tri-system integration in metal-oxide nanocomposites via in-situ solution-processed method for ultrathin flexible transparent electrodes

For stable operation of ultrathin flexible transparent electrodes (uFTEs), it is critical to implement effective risk management during concurrent multi-loading operation of electrical bias and mechanical folding cycles in high-humidity environments. Despite extensive efforts in preparing solution-processed uFTEs with cost-effective and high-throughput means, achieving in-situ nano-adhesion in heterogeneous metal-oxide nanocomposites remains challenging. In this work, we observed by serendipity liquid-like behaviour of transparent metal-oxide-semiconductor zinc oxide nanoparticles (ZnONPs) onto silver nanowires (AgNWs) developed by in-situ solution processed method (iSPM). This enabled us to address the long-standing issue of vulnerability in the nanocomposite caused by the interface of dissimilar materials between AgNWs and ZnONPs, resulting in a remarkably improved multi-loading operation. Importantly, substrate-integrated uFTEs constituted of the metal-oxide nanocomposite electrode semi-embedded in the polymer matrix of greatly thin <0.5 μm thickness is successfully demonstrated with the smooth surface topography, promoted by the tri-system integration including (i) AgNW-AgNW, (ii) ZnONP-ZnONP, and (iii) AgNW-ZnONP systems. Our finding unveils the complex interfacial dynamics associated with the heterogeneous interface system between AgNWs and ZnONPs and holds great promise in understanding the in-situ nano-adhesion process and increasing the design flexibility of next generation solution-processed uFTEs.

Materials-Driven Soft Wearable Bioelectronics for Connected Healthcare

In the era of Internet-of-things, many things can stay connected; however, biological systems, including those necessary for human health, remain unable to stay connected to the global Internet due to the lack of soft conformal biosensors. The fundamental challenge lies in the fact that electronics and biology are distinct and incompatible, as they are based on different materials via different functioning principles. In particular, the human body is soft and curvilinear, yet electronics are typically rigid and planar. Recent advances in materials and materials design have generated tremendous opportunities to design soft wearable bioelectronics, which may bridge the gap, enabling the ultimate dream of connected healthcare for anyone, anytime, and anywhere. We begin with a review of the historical development of healthcare, indicating the significant trend of connected healthcare. This is followed by the focal point of discussion about new materials and materials design, particularly low-dimensional nanomaterials. We summarize material types and their attributes for designing soft bioelectronic sensors; we also cover their synthesis and fabrication methods, including top-down, bottom-up, and their combined approaches. Next, we discuss the wearable energy challenges and progress made to date. In addition to front-end wearable devices, we also describe back-end machine learning algorithms, artificial intelligence, telecommunication, and software. Afterward, we describe the integration of soft wearable bioelectronic systems which have been applied in various testbeds in real-world settings, including laboratories that are preclinical and clinical environments. Finally, we narrate the remaining challenges and opportunities in conjunction with our perspectives.

Highly Flexible and Acid-Alkali Resistant TiN Nanomesh Transparent Electrodes for Next-Generation Optoelectronic Devices

Transparent electrodes are vital for optoelectronic devices, but their development has been constrained by the limitations of existing materials such as indium tin oxide (ITO) and newer alternatives. All face issues of robustness, flexibility, conductivity, and stability in harsh environments. Addressing this challenge, we developed a flexible, low-cost titanium nitride (TiN) nanomesh transparent electrode showcasing exceptional acid-alkali resistance. The TiN nanomesh electrode, created by depositing a TiN coating on a naturally cracked gel film substrate via a sputtering method, maintains a stable electrical performance through thousands of bending cycles. It exhibits outstanding chemical stability, resisting strong acid and alkali corrosion, which is a key hurdle for current electrodes when in contact with acidic/alkaline materials and solvents during device fabrication. This, coupled with superior light transmission and conductivity (88% at 550 nm with a sheet resistance of ∼200 Ω/sq), challenges the reliance on conventional materials. Our TiN nanomesh electrode, successfully applied in electric heaters and electrically controlled thermochromic devices, offers broad potential beyond harsh environment applications. It enables alternative possibilities for the design and fabrication of future optoelectronics for advancements in this pivotal field.

Porous carbon nanosheets derived from two-dimensional Fe-MOF for simultaneous voltammetric sensing of dopamine and uric acid

It is of great significance for electrochemical sensors to simultaneously detect dopamine (DA) and uric acid (UA) related to biological metabolism. In this work, two-dimensional (2D) porous carbon nanosheets (CNS) was prepared as electrocatalysts to improve the sensitivity, the selectivity, and the detection limit of the simultaneous detection. First, 2D amorphous iron-metal organic frameworks (Fe-MOF) was synthesized with Fe3+and terephthalic acid via a facile wet chemistry method at room temperature. And then, CNS was prepared by pyrolysis and pickling of Fe-MOF. CNS had large specific surface area, good electrical conductivity and lots of carbon defects. The response currents of the CNS modified electrode was larger than those of the control electrodes in the simultaneous determination. The simultaneous determination was measured via differential pulse voltammetry to reduce the effect of capacitive currents on quantitative analysis. The CNS modified electrodes showed high sensitivity and low detection limit for the simultaneous detection of DA and UA. The modified electrodes have been successfully used to detect DA and UA in normal human serum.

Tunable Magnetic Domain Patterns in Thickness-Gradient Nickel Films on Flexible PDMS Substrates

Flexible magnetoelectronic devices (based on magnetic films) have great application prospects in the fields of information storages, bionic robotics, and electronic skins. The intrinsic stress and external loading are very important to modulate the structures and properties of flexible magnetic films due to the magnetoelastic coupling effect. Here, we report on tunable magnetic domain patterns in thickness-gradient nickel (Ni) films deposited on flexible polydimethylsiloxane substrates. It is found that stripe magnetic domains spontaneously form in the Ni films and their sizes increase with the film thickness. The internal stress evolves from tensile to compressive states with decreasing film thickness, leading to the formation of cracks in thicker regions and wrinkles in thinner regions. Meanwhile, the orientations of stripe magnetic domains change from the gradient direction to the orthogonal direction. The structural features, evolution behaviors, and physical mechanisms of the cracks, wrinkles, and magnetic domains are analyzed based on the stress theory and magnetoelastic coupling. Periodic gradient Ni films with large-scale regulations of stripe magnetic domains are also realized by masking of copper grids. This study helps to better understand the magnetoelastic coupling effect in gradient flexible magnetic films and provides a technique to modulate anisotropic magnetic properties by designing specific film systems.

An Aqueous Process for Preparing Flexible Transparent Electrodes Using Non-Oxidized Graphene/Single-Walled Carbon Nanotube Hybrid Solution

In this study, we prepared flexible and transparent hybrid electrodes based on an aqueous solution of non-oxidized graphene and single-walled carbon nanotubes. We used a simple halogen intercalation method to obtain high-quality graphene flakes without a redox process and prepared hybrid films using aqueous solutions of graphene, single-walled carbon nanotubes, and sodium dodecyl sulfate surfactant. The hybrid films showed excellent electrode properties, such as an optical transmittance of ≥90%, a sheet resistance of ~3.5 kΩ/sq., a flexibility of up to ε = 3.6% ((R) = 1.4 mm), and a high mechanical stability, even after 103 bending cycles at ε = 2.0% ((R) = 2.5 mm). Using the hybrid electrodes, thin-film transistors (TFTs) were fabricated, which exhibited an electron mobility of ~6.7 cm2 V-1 s-1, a current on-off ratio of ~1.04 × 107, and a subthreshold voltage of ~0.122 V/decade. These electrical properties are comparable with those of TFTs fabricated using Al electrodes. This suggests the possibility of customizing flexible transparent electrodes within a carbon nanomaterial system.