Showing papers in "Advanced materials and technologies in 2021"

Recent Progress on Flexible Capacitive Pressure Sensors: From Design and Materials to Applications

Abstract: The authors acknowledge the generous support of King Abdullah University of Science and Technology (KAUST). The authors thank Kelly Rader for proofreading this manuscript.

Perovskite Solar Cells with All‐Inkjet‐Printed Absorber and Charge Transport Layers

Abstract: The power conversion efficiency (PCE) of incident solar irradiation to electrical power is the key indicator to rate photovoltaic (PV) technologies. Due to rapid increase in reported best researchcell PCEs over the past decade, the field of hybrid organic–inorganic lead halide perovskite PV has attracted enormous attention within the PV community. PCEs of up to 25.2% are certified for perovskite solar cells (PSCs) on laboratory scale, narrowing the gap toward the record for crystalline silicon solar cells of >26% although there is still a significant difference in the active area size.[1–3] Tandem cells combining low-bandgap silicon bottom solar cells and wide-bandgap perovskite top solar cells promise PCEs exceeding the Shockley–Queisser limit of single cells[4,5], with current record devices already achieving over 29%[1,6–8]. However, in order to commercialize perovskite PV as single-junctionor tandem-PV-technology, strategies to upscale PSCs while maintaining high PCEs have to be developed. There are two competing technical approaches for upscaling perovskite photovoltaics: On the one hand all-evaporated PSCs using vacuum-based deposition techniques[9,10] and on the other hand solution-based coating and printing techniques for PSCs[11]. Scalable solutionbased techniques that have been employed in recent years are blade coating[12,13], slot-die coating,[14,15] and inkjet printing[16–20]. While all of these techniques promise fast and scalable material deposition, inkjet printing stands out due to the precise control of small droplets allowing free choice of printing patterns[21,22] and efficient material usage.[23] Inkjet printing has already demonstrated its potential for fully-printed organic solar cells[24,25] and organic photo detectors[26]. Moreover, it is recently on the rise for mass fabrication of displays with organic light emitting diodes[27–31]. PSCs with an inkjet-printed (IJP) perovskite absorber layer demonstrated steadily increasing PCEs over the past years resulting in maximum PCEs of over 21% in single scan measurements and over 18% stabilized power conversion efficiency (SPCE), as we showed in our previous publication.[22] However, PSCs not only consist of the perovskite absorber layer, but also charge transport layers and electrodes. In contrast to many other deposition techniques for transferring the promising results on IJP perovskite layers to an industrial-scale fabrication, One of the key challenges of perovskite photovoltaics is the scalable fabrication of high-efficiency perovskite solar cells (PSCs). Not only the scalable deposition of high-quality perovskite thin-films itself, but also the adjacent charge extraction layers is pivotal. In this work, PSCs based on all-inkjet-printed absorber and extraction layers are presented, allowing for a scalable and material-efficient deposition. The inkjet-printed PSCs are of p–i–n-architecture with a precursor-based nickel oxide hole-transport layer, a high-quality inkjet-printed triple-cation (methylammonium, formamidinium, and cesium) perovskite absorber layer and a double layer electron-transport layer of phenyl-C61-butyric acid methyl ester and bathocuproine. The ink properties, inkjet parameters, and annealing procedure are optimized for each layer. PSCs with such inkjet-printed absorber and charge carrier extraction layers demonstrate an efficiency of >17% with low hysteresis. Although printed in ambient atmosphere, the devices show excellent short-term stability (40 h) even under elevated temperature (85 °C). These results are a promising next step on the way to fully inkjet-printed perovskite solar cells, including both electrodes as well.

Electrospun Adsorptive Nanofibrous Membranes from Ion Exchange Polymers to Snare Textile Dyes from Wastewater

Abstract: F.T. and M.A.A. gratefully acknowledges the postdoctoral fellowships from King Abdullah University of Science and Technology (KAUST). The research reported in this publication was supported by funding from KAUST. L.C. is grateful for the PhD scholarship from the University of Manchester. A.A. acknowledges the PhD scholarship from Saudi Aramco. To follow the group's research activities visit www.szekelygroup.com.

Wearable Sensors for Remote Health Monitoring: Potential Applications for Early Diagnosis of Covid-19

Abstract: Wearable sensors are emerging as a new technology to detect physiological and biochemical markers for remote health monitoring. By measuring vital signs such as respiratory rate, body temperature, and blood oxygen level, wearable sensors offer tremendous potential for the noninvasive and early diagnosis of numerous diseases such as Covid-19. Over the past decade, significant progress has been made to develop wearable sensors with high sensitivity, accuracy, flexibility, and stretchability, bringing to reality a new paradigm of remote health monitoring. In this review paper, the latest advances in wearable sensor systems that can measure vital signs at an accuracy level matching those of point-of-care tests are presented. In particular, the focus of this review is placed on wearable sensors for measuring respiratory behavior, body temperature, and blood oxygen level, which are identified as the critical signals for diagnosing and monitoring Covid-19. Various designs based on different materials and working mechanisms are summarized. This review is concluded by identifying the remaining challenges and future opportunities for this emerging field.

Ultrasensitive Detection of Dopamine, IL-6 and SARS-CoV-2 Proteins on Crumpled Graphene FET Biosensor

Abstract: Universal platforms for biomolecular analysis using label-free sensing modalities can address important diagnostic challenges. Electrical field effect-sensors are an important class of devices that can enable point-of-care sensing by probing the charge in the biological entities. Use of crumpled graphene for this application is especially promising. It is previously reported that the limit of detection (LoD) on electrical field effect-based sensors using DNA molecules on the crumpled graphene FET (field-effect transistor) platform. Here, the crumpled graphene FET-based biosensing of important biomarkers including small molecules and proteins is reported. The performance of devices is systematically evaluated and optimized by studying the effect of the crumpling ratio on electrical double layer (EDL) formation and bandgap opening on the graphene. It is also shown that a small and electroneutral molecule dopamine can be captured by an aptamer and its conformation change induced electrical signal changes. Three kinds of proteins were captured with specific antibodies including interleukin-6 (IL-6) and two viral proteins. All tested biomarkers are detectable with the highest sensitivity reported on the electrical platform. Significantly, two COVID-19 related proteins, nucleocapsid (N-) and spike (S-) proteins antigens are successfully detected with extremely low LoDs. This electrical antigen tests can contribute to the challenge of rapid, point-of-care diagnostics.

Free-Fixed Rotational Triboelectric Nanogenerator for Self-Powered Real-Time Wheel Monitoring

Abstract: Transportation has always been necessary for propelling the development of human civilization.[1,2] For example, railway networks save much time and bring immeasurable economic benefits.[3] As a common sense, safety is a precondition for railway operation. Consequently, as a crucial and wear-prone component, wheel attracts considerable attention due to its health and stability monitoring.[4–6] However, the sensors for detection are usually powered by traditional cables, requiring wear-proof collecting rings with complex wire management. On the other hand, although energy storage devices including batteries and supercapacitors have a rapid development these years,[7–11] they constantly need to be replaced and cause potential environment damage due to the toxic materials used in the fabrication process. As the world entering the era of internet of things (IoTs),[12–14] self-powered technology for sensors by harvesting environment energy is derived since the power needed to operate each sensor is small.[15–21] Self-powered technology by triboelectric nanogenerators (TENGs) shows great potential for distributed power sources with advantages of cost effective, light weight, and high conversion efficiency.[18,22–27] Moreover, large amounts of mechanical energy on wheels are proved to be harvested by TENGs, according to previous works.[28–30] Even so, the development of TENGs for train wheels is still hindered because of the special structure of train. Widely applied in many fields, TENG is highlighted for its variable structure in special application environment, such as medicine,[31,32] constructions,[33,34] blue energy,[35–37] and so on. In this regard, designing a new structure of TENG for acclimatization is highly desirable and mandatory. In this work, we proposed a free-fixed TENG (FF-TENG) with rotation mode for wheel train monitoring by fixing magnets on the stator and bogie. Thus, the stator is not fixed directly on the bogie, without a serious negative impact on the wheel. The magnetic force not only immobilizes the stator, but also increases the contact areas between the stator and rotator to improve output. With the rational structure design, FF-TENG delivers a short-circuit current of 55 μA, an open-circuit voltage Developing an applicable triboelectric nanogenerator (TENG) for train wheel energy harvesting is a key step to meet the urgent need of wheel safety monitoring. Herein, an innovative design of free-fixed TENG (FFTENG) is reported, without a serious negative impact on the wheel. The key of this design is the magnets fixed on the device and bogie, providing attractive force to immobilize the stator. With a rotational structure, FF-TENG can provide a high short-circuit current of 55 μA, an opencircuit voltage of 500 V, and a charge of 235 nC at a rotation speed of 400 rpm. At an external load resistance of 10 MΩ, FF-TENG delivers the maximum power of 15.68 mW. Furthermore, the superior robustness of FF-TENG in vibration environment is proved. In addition, a power management circuit designed by LTC 3588 is tested for more efficient capacitor charging, leading to better performance to power electronics. Finally, a self-powered real-time wheel temperature and wheel speed monitoring system is developed with FF-TENG as a safety alert demo for feasibility demonstration. Given the rational structure design and high performance, this work paves a practical way for TENGs in the field of intelligent transportation.

Bio-Inspired Artificial Vision and Neuromorphic Image Processing Devices

Abstract: DOI: 10.1002/admt.202100144 processing devices.[1–6] However, conventional image recognition systems using a flat image sensor array with a multilens optical system and the von-Neumann computing architecture for processing the acquired image data have several limitations such as high system-level complexity, bulky module size, large computing load, and low energy efficiency.[7] Therefore, advanced devices in both image acquisition and image data processing are required. As a result, bio-inspired imaging devices[8–10] (i.e., artificial vision) and neuromorphic image processing devices[11–13] (i.e., artificial synapse) have received considerable attention (Figure 1). Bio-inspired imaging devices (e.g., bioinspired camera) have been developed for image acquisition.[14] Conventional imaging devices require bulky and heavy optical systems to obtain high-quality visual information.[15] In contrast, natural eyes have a simple and small optical geometry and high-quality image acquisition capability.[16,17] Therefore, bio-inspired artificial vision has been developed by mimicking the unique structural and functional advantage of natural eyes[2,6] (Figure 1a). For example, the chambered eye, typically found in humans and aquatic animals, exhibits a wide field of view, low optical aberration, and facile accommodation with a simple optical system.[16,17] The compound eye has distinctive optical geometries, and such structures offer various useful visual features.[18,19] Neuromorphic computing devices that can efficiently process massive image data acquired from the imaging device have been developed for image data processing.[20–22] The conventional vonNeumann architecture, in which the central processing unit and memory unit are separated, is not suitable to efficiently process the massive unstructured image data.[23,24] Therefore, a novel computing device inspired by the human brain (i.e., electronic synapse) has been developed[25,26] (Figure 1b). For example, the memristor crossbar array can efficiently perform vector multiplications.[27] Such a neuromorphic device implements artificial neural networks (ANN) in the hardware and enables efficient parallel processing of image data with low energy consumption.[25] In a previous study, a device that integrates the synaptic device and photodetector in one unit has been reported.[26] Despite recent progress in the hardware of the neuromorphic image data processing devices, such devices still require Remarkable technological developments for efficient image recognition (i.e., image acquisition and image data processing) have been reported in the past decade. Such advances in imaging and image processing technologies have driven significant progress in mobile electronics and machine vision applications. In particular, for image acquisition devices, two types of natural eyes (i.e., chambered and compound eyes) have inspired the development of novel multifunctional imaging devices with unique optical geometries. For image data processing devices, novel computing devices based on memristor crossbar arrays, such as electronic synapses, have been developed. More recently, the integration of imaging and image processing devices in a single unit further enhances the system-level efficiency. Herein, such recent advances in the bio-inspired artificial vision and neuromorphic image processing devices, aimed at providing efficient image recognition, are reviewed. First, various imaging devices inspired by the structural and functional features of natural eyes are introduced. Second, artificial synapses and their operation principles are thoroughly discussed. Third, the neuromorphic vision sensor that integrates the imaging and image processing devices is reviewed. Finally, a brief summary and future outlook are presented.

Swing-Structured Triboelectric–Electromagnetic Hybridized Nanogenerator for Breeze Wind Energy Harvesting

Abstract: DOI: 10.1002/admt.202100496 environmental pollution problems.[3,4] Under such circumstances, it is desirable to search for new clean and renewable energy sources from our environment, such as widely distributed wind energy in nature.[5] Harvesting wind energy has attracted increasing attention in the past decades.[6] Nowadays, the main way to exploit the wind energy is to drive the wind turbine blades to rotate by the wind force, converting the wind energy into mechanical energy, and then drive the electromagnetic generator (EMG) to generate electricity through the speedincrease gearbox.[7] Due to the technology limitations, it is rather challenging to collect irregular, random, and low-speed wind energy by using the EMG, with the main drawbacks of complex structure, large volume, and low energy conversion efficiency.[8,9] However, the emerging triboelectric nanogenerator (TENG) provides a new strategy for the efficient utilization of breeze wind energy.[10] The TENG, also called as Wang generator, is a powerful mechanical energy harvesting technology, based on the coupling of triboelectrification and electrostatic induction.[11,12] Due to its fundamental mechanism of Maxwell’s displacement current, it exhibits obvious advantage over the EMG at low frequency.[13,14] And, the TENG technology has been widely applied to scavenge the Wind energy is one of the most promising renewable energy sources, but harvesting low frequency breeze wind energy is hardly achieved using traditional electromagnetic generators (EMGs). Triboelectric nanogenerators (TENGs) provide a new approach for large-scale collection of distributed breeze wind energy (usually 3.4–5.4 m s−1). Herein, by coupling the TENG and EMG, a swing-structured hybrid nanogenerator with improved performance and durability is designed. The dielectric brush and air gap designs can minimize the material wear and continuously supply the tribo-charges. Under external triggering, systematic comparisons are made about the output characteristics of TENG and EMG. The rectified peak power and average power of TENG are respectively, 60 and 635 times higher than those of EMG at moderate coil turn numbers, showing that TENG is much more effective than EMG for harvesting low-frequency distributed energy (high entropy energy). Furthermore, the hybrid nanogenerator and array device are hung on tree branches to demonstrate the effective harvesting of breeze wind energy, delivering total rectified peak power densities of 2.07 and 1.94 W m–3 for single and array devices, respectively. The applications of powering portable electronics reveal the huge prospects of hybrid nanogenerator in self-powered environmental monitoring toward forest/park fire warning systems.