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  • Laser-induced hierarchical carbon patterns on polyimide substrates for flexible urea sensors
    npj Flex. Electron. Pub Date : 2019-01-10
    Emil R. Mamleyev, Stefan Heissler, Alexei Nefedov, Peter G. Weidler, Nurdiana Nordin, Vladislav V. Kudryashov, Kerstin Länge, Neil MacKinnon, Swati Sharma

    Thermochemical decomposition of organic materials under heat-treatment in the absence of oxygen, known as the pyrolysis process, is often employed to convert micro and nano patterned polymers into carbon structures, which are subsequently used as device components. Pyrolysis is performed at ≥900 °C, which entails substrate materials with a high thermal stability that excludes flexible, polymeric substrates. We use optimized laser radiation to pattern graphitic carbon structures onto commercially available polyimide (Kapton) sheets in the micrometer to millimeter scale by inducing a localized, rapid pyrolysis, for the fabrication of flexible devices. Resulting laser carbon films are electrically conductive and exhibit a high-surface area with a hierarchical porosity distribution along their cross-section. The material is obtained using various combinations of laser parameters and pyrolysis environment (oxygen-containing and inert). Extensive characterization of laser carbon is performed to understand the correlation between the material properties and laser parameters, primarily fluence and power. A photothermal carbonization mechanism based on the plume formation is proposed. Further, laser carbon is used for the fabrication of enzymatic, pH-based urea sensors using two approaches: (i) direct urease enzyme immobilization onto carbon and (ii) electrodeposition of an intermediate chitosan layer prior to urease immobilization. This flexible sensor is tested for quantitative urea detection down to 10−4 M concentrations, while a qualitative, color-indicative test is performed on a folded sensor placed inside a tube to demonstrate its compatibility with catheters. Laser carbon is suitable for a variety of other flexible electronics and sensors, can be conveniently integrated with an external circuitry, heating elements, and with other microfabrication techniques such as fluidic platforms.

    更新日期:2019-01-10
  • Energy autonomous electronic skin
    npj Flex. Electron. Pub Date : 2019-01-04
    Carlos García Núñez, Libu Manjakkal, Ravinder Dahiya

    Energy autonomy is key to the next generation portable and wearable systems for several applications. Among these, the electronic-skin or e-skin is currently a matter of intensive investigations due to its wider applicability in areas, ranging from robotics to digital health, fashion and internet of things (IoT). The high density of multiple types of electronic components (e.g. sensors, actuators, electronics, etc.) required in e-skin, and the need to power them without adding heavy batteries, have fuelled the development of compact flexible energy systems to realize self-powered or energy-autonomous e-skin. The compact and wearable energy systems consisting of energy harvesters, energy storage devices, low-power electronics and efficient/wireless power transfer-based technologies, are expected to revolutionize the market for wearable systems and in particular for e-skin. This paper reviews the development in the field of self-powered e-skin, particularly focussing on the available energy-harvesting technologies, high capacity energy storage devices, and high efficiency power transmission systems. The paper highlights the key challenges, critical design strategies, and most promising materials for the development of an energy-autonomous e-skin for robotics, prosthetics and wearable systems. This paper will complement other reviews on e-skin, which have focussed on the type of sensors and electronics components.

    更新日期:2019-01-04
  • Reversible conductivity recovery of highly sensitive flexible devices by water vapor
    npj Flex. Electron. Pub Date : 2018-12-21
    Yuting Wang, Yingchun Su, Zegao Wang, Zhongyang Zhang, Xiaojun Han, Mingdong Dong, Lifeng Cui, Menglin Chen

    With decreasing size of integrated circuits in wearable electronic devices, the circuit is more susceptible to aging or fracture problem, subsequently decreasing the transmission efficiency of electricity. Micro-healing represents a good approach to solve this problem. Herein, we report a water vapor method to repair microfiber-based electrodes by precise positioning and rapid healing at their original fracture sites. To realize this micro-level conducting healing, we utilize a bimaterial composed of polymeric microfibers as healing agents and electrically conductive species on its surface. This composite electrode shows a high-performance conductivity, great transparency, and ultra-flexibility. The transmittance of our electrode could reach up to 88 and 90% with a sheet resistance of 1 and 2.8 Ω sq−1, respectively, which might be the best performance among Au-based materials as we know. Moreover, after tensile failure, water vapor is introduced to mediate heat transfer for the healing process, and within seconds the network electrode could be healed along with recovering of its resistance. The recovering process could be attributed to the combination of adhesion force and capillary force at this bimaterial interface. Finally, this functional network is fabricated as a wearable pressure/ strain sensing device. It shows excellent stretchability and mechanical durability upon 1000 cycles.

    更新日期:2018-12-21
  • A fully inkjet-printed disposable glucose sensor on paper
    npj Flex. Electron. Pub Date : 2018-12-03
    Eloïse Bihar, Shofarul Wustoni, Anna Maria Pappa, Khaled N. Salama, Derya Baran, Sahika Inal

    Inexpensive and easy-to-use diagnostic tools for fast health screening are imperative, especially in the developing world, where portability and affordability are a necessity. Accurate monitoring of metabolite levels can provide useful information regarding key metabolic activities of the body and detect the concomitant irregularities such as in the case of diabetes, a worldwide chronic disease. Today, the majority of daily glucose monitoring tools rely on piercing the skin to draw blood. The pain and discomfort associated with finger pricking have created a global need to develop non-invasive, portable glucose assays. In this work, we develop a disposable analytical device which can measure physiologically relevant glucose concentrations in human saliva based on enzymatic electrochemical detection. We use inkjet-printing technology for the rapid and low-cost deposition of all the components of this glucose sensor, from the electronics to the biorecognition elements, on commercially available paper substrates. The only electronic component of the sensor is the conducting polymer poly(3,4 ethylenedioxythiophene) doped with polystyrene sulfonate (PEDOT:PSS), while the biorecognition element comprises of the enzyme glucose oxidase coupled with an electron mediator. We demonstrate that one month after its fabrication and storage in air-free environment, the sensor maintains its function with only minor performance loss. This fully printed, all-polymer biosensor with its ease of fabrication, accuracy, sensitivity and compatibility with easy-to-obtain biofluids such as saliva aids in the development of next generation low-cost, non-invasive, eco-friendly, and disposable diagnostic tools.

    更新日期:2018-12-03
  • Direct writing of anodic oxides for plastic electronics
    npj Flex. Electron. Pub Date : 2018-08-28
    Christian Michael Siket, Nadine Tillner, Andrei Ionut Mardare, Amir Reuveny, Carina Daniela Grill, Florian Hartmann, Gerald Kettlgruber, Richard Moser, Jan Philipp Kollender, Takao Someya, Achim Walter Hassel, Martin Kaltenbrunner, Siegfried Bauer

    Metal oxide thin films for soft and flexible electronics require low cost, room temperature fabrication, and structuring processes. We here introduce an anodic printing process to realize the essential building blocks of electronic circuitry, including resistors, capacitors, field-effect transistors, diodes, rectifiers, and memristors directly on imperceptible plastic substrates. Largely independent on surface properties, we achieve high-quality, few nanometer thin dielectric and semiconducting films even on rough substrates via localized anodisation of valve metals using a scanning droplet cell microscope. We demonstrate printing-like fabrication of 3D multilayer solid-state capacitors with a record-high areal capacity of 4 µF cm−2. Applicable to the whole class of valve metals and their alloys, our method provides a versatile fabrication technique for the circuits that empower the flexible and stretchable electronics of tomorrow.

    更新日期:2018-11-29
  • Defects engineering for high-performance perovskite solar cells
    npj Flex. Electron. Pub Date : 2018-08-14
    Feng Wang, Sai Bai, Wolfgang Tress, Anders Hagfeldt, Feng Gao

    Metal halide perovskites have achieved great success in photovoltaic applications during the last few years. The solar to electrical power conversion efficiency (PCE) of perovskite solar cells has been rapidly improved from 3.9% to certified 22.7% due to the extensive efforts on film deposition methods, composition and device engineering. Further investigation on eliminating the defect states in perovskite absorbers is necessary to push forward the PCE of perovskite solar cells approaching the Shockley-Queisser limit. In this review, we summarize the defect properties in perovskite films and present methodologies to control the defects density, including the growth of large size crystals, photo-curing method, grain boundary and surface passivation, and modification of the substrates. We also discuss the defects-related stability and hysteresis issues and highlight the current challenges and opportunities in defects control of perovskite films.

    更新日期:2018-11-29
  • 2D organic molecular metallic soft material derived from BEDO-TTF with electrochromic and rectifying properties
    npj Flex. Electron. Pub Date : 2018-11-08
    Daniel Suarez, Eden Steven, Elena Laukhina, Andres Gomez, Anna Crespi, Narcis Mestres, Concepció Rovira, Eun Sang Choi, Jaume Veciana

    In this article we demonstrate that a migration of iodine species and chemical transformation in a moist environment induced by a voltage-biased Pt electrode is able to alter the color and degree of charge transfer in a layer of the 2D organic molecular metal (BEDO-TTF)2.4I3 [BEDO = bis(ethylenedioxy)tetrathiafulvalene] self-assembled at the surface of a polycarbonate film. These effects produce a reversible electrochromic behavior of the layer with low operating voltages and fast operation times. Adjuvant with electrochromism, this flexible material exhibits rectifying behavior whose I-V curves are dependent on the voltage sweep directions. These results open new possibilities for the design and fabrication of organic flexible materials for soft electrochromic and rectifying components. The easy working principle ensures reliability, low power consumption, and versatility through its implementation into simple devices. Such working principle has been confirmed by temperature dependent resistance measurements, X-Ray, EDX-SEM, and conducting-AFM studies.

    更新日期:2018-11-08
  • Kinetics of thermally activated triplet fusion as a function of polymer chain packing in boosting the efficiency of organic light emitting diodes
    npj Flex. Electron. Pub Date : 2018-11-01
    Amrita Dey, Naresh Chandrasekaran, Dwaipayan Chakraborty, Priya Johari, Christopher R. McNeill, Akshay Rao, Dinesh Kabra

    Understanding the photophysical process governing the operation of the organic light emitting diodes (OLEDs) and how they are affected by film morphology is crucial to the efficient design of future OLEDs. In particular, delayed fluorescence (DF), is known to contribute a significant fraction of the light emission from polymer-based OLEDs, but its mechanism remains unclear. Here, we investigate the origin of DF in the state of the art OLED polymer Poly (9, 9-dioctylfluorene-alt-benzothiadiazole) (F8BT), under both optical and electrical excitation using time-resolved emission spectroscopy (TRES) as a function of film thickness, excitation fluence, magnetic-field, and temperature. The temperature dependence of the DF for various film thicknesses suggests that thermally activated triplet migration is the dominant process controlling DF at room temperature. We found that thermal activation energy (Eeff) of triplet migration decreases from 179 ± 31 meV to 86 ± 11 meV as film thickness varied from ~110 nm to ~560 nm, respectively. The Eeff of triplet migration is found to be a function of the molecular packing of polymer chains as determined from synchrotron grazing incidence wide angle x-ray scattering (GIWAXS) studies and steady-state photoluminescence studies. Quantum chemical calculations of reorganization energy and singlet–triplet exchange energy gap in F8BT molecule as a function of the dihedral angle between donor & acceptor moiety also confirm the experimental results. Our results show that DF in polymer OLEDs is significantly affected by parameters such as the film thickness and disorder, allowing for a high degree of control over the underlying photophysics to be achieved.

    更新日期:2018-11-02
  • An external quantum efficiency of >20% from solution-processed poly(dendrimer) organic light-emitting diodes
    npj Flex. Electron. Pub Date : 2018-10-23
    Fatemeh Maasoumi, Ross D. Jansen-van Vuuren, Paul E. Shaw, Emma V. Puttock, Ravi Chandra Raju Nagiri, Jake A. McEwan, Mark Bown, Jenny L. O’Connell, Christopher J. Dunn, Paul L. Burn, Ebinazar B. Namdas

    Controlling the orientation of the emissive dipole has led to a renaissance of organic light-emitting diode (OLED) research, with external quantum efficiencies (EQEs) of >30% being reported for phosphorescent emitters. These highly efficient OLEDs are generally manufactured using evaporative methods and are comprised of small-molecule heteroleptic phosphorescent iridium(III) complexes blended with a host and additional layers to balance charge injection and transport. Large area OLEDs for lighting and display applications would benefit from low-cost solution processing, provided that high EQEs could be achieved. Here, we show that poly(dendrimer)s consisting of a non-conjugated polymer backbone with iridium(III) complexes forming the cores of first-generation dendrimer side chains can be co-deposited with a host by solution processing to give highly efficient devices. Simple bilayer devices comprising the emissive layer and an electron transport layer gave an EQE of >20% at luminances of up to ≈300 cd/m2, showing that polymer engineering can enable alignment of the emissive dipole of solution-processed phosphorescent materials.

    更新日期:2018-10-23
  • Transfer printing techniques for flexible and stretchable inorganic electronics
    npj Flex. Electron. Pub Date : 2018-10-08
    Changhong Linghu, Shun Zhang, Chengjun Wang, Jizhou Song

    Transfer printing is an emerging deterministic assembly technique for micro-fabrication and nano-fabrication, which enables the heterogeneous integration of classes of materials into desired functional layouts. It creates engineering opportunities in the area of flexible and stretchable inorganic electronics with equal performance to conventional wafer-based devices but the ability to be deformed like a rubber, where prefabricated inorganic semiconductor materials or devices on the donor wafer are required to be transfer-printed onto unconventional flexible substrates. This paper provides a brief review of recent advances on transfer printing techniques for flexible and stretchable inorganic electronics. The basic concept for each transfer printing technique is overviewed. The performances of these transfer printing techniques are summarized and compared followed by the discussions of perspectives and challenges for future developments and applications.

    更新日期:2018-10-08
  • Graphene electronic fibres with touch-sensing and light-emitting functionalities for smart textiles
    npj Flex. Electron. Pub Date : 2018-09-25
    Elias Torres Alonso, Daniela P. Rodrigues, Mukond Khetani, Dong-Wook Shin, Adolfo De Sanctis, Hugo Joulie, Isabel de Schrijver, Anna Baldycheva, Helena Alves, Ana I. S. Neves, Saverio Russo, Monica F. Craciun

    The true integration of electronics into textiles requires the fabrication of devices directly on the fibre itself using high-performance materials that allow seamless incorporation into fabrics. Woven electronics and opto-electronics, attained by intertwined fibres with complementary functions are the emerging and most ambitious technological and scientific frontier. Here we demonstrate graphene-enabled functional devices directly fabricated on textile fibres and attained by weaving graphene electronic fibres in a fabric. Capacitive touch-sensors and light-emitting devices were produced using a roll-to-roll-compatible patterning technique, opening new avenues for woven textile electronics. Finally, the demonstration of fabric-enabled pixels for displays and position sensitive functions is a gateway for novel electronic skin, wearable electronic and smart textile applications.

    更新日期:2018-09-25
  • Compliant plant wearables for localized microclimate and plant growth monitoring
    npj Flex. Electron. Pub Date : 2018-09-10
    Joanna M. Nassar, Sherjeel M. Khan, Diego Rosas Villalva, Maha M. Nour, Amani S. Almuslem, Muhammad M. Hussain

    The microclimate surrounding a plant has major effect on its health and photosynthesis process, where certain plants struggle in suboptimal environmental conditions and unbalanced levels of humidity and temperature. The ability to remotely track and correlate the effect of local environmental conditions on the healthy growth of plants can have great impact for increasing survival rate of plants and augmenting agriculture output. This necessitates the widespread distribution of lightweight sensory devices on the surface of each plant. Using flexible and biocompatible materials coupled with a smart compact design for a low power and lightweight system, we develop widely deployed, autonomous, and compliant wearables for plants. The demonstrated wearables integrate temperature, humidity and strain sensors, and can be intimately deployed on the soft surface of any plant to remotely and continuously evaluate optimal growth settings. This is enabled through simultaneous detection of environmental conditions while quantitatively tracking the growth rate (viz. elongation). Finally, we establish a nature-inspired origami-assembled 3D-printed “PlantCopter”, used as a launching platform for our plant wearable to enable widespread microclimate monitoring in large fields.

    更新日期:2018-09-10
  • The formation of perovskite multiple quantum well structures for high performance light-emitting diodes
    npj Flex. Electron. Pub Date : 2018-04-23
    Yan Sun, Li Zhang, Nana Wang, Shuting Zhang, Yu Cao, Yanfeng Miao, Mengmeng Xu, Hao Zhang, Hai Li, Chang Yi, Jianpu Wang, Wei Huang

    Recent works showed that high efficient perovskite light-emitting diodes can be achieved from solution-processed, self-organized multiple quantum wells (MQWs) with an energy cascade. We investigate how the mixing of QWs with different band gaps can affect the perovskite LED device performance. We find that the annealing process can significantly affect the constitution of the MQWs films, where the dominant phase can evolve from large band gap QWs to small band gap QWs. The optimal constitution for LED application lies in a transition point of small-n QWs dominant phase to large-n QWs dominant phase, when the MQW film presents highest photoluminescence while still remains uniform film morphology.

    更新日期:2018-07-14
  • Compliant lightweight non-invasive standalone “Marine Skin” tagging system
    npj Flex. Electron. Pub Date : 2018-05-03
    Joanna M. Nassar, Sherjeel M. Khan, Seneca J. Velling, Andrea Diaz-Gaxiola, Sohail F. Shaikh, Nathan R. Geraldi, Galo A. Torres Sevilla, Carlos M. Duarte, Muhammad M. Hussain

    Current marine research primarily depends on weighty and invasive sensory equipment and telemetric network to understand the marine environment, including the diverse fauna it contains, as a function of animal behavior and size, as well as equipment longevity. To match animal morphology and activity within the surrounding marine environment, here we show a physically flexible and stretchable skin-like and waterproof autonomous multifunctional system, integrating Bluetooth, memory chip, and high performance physical sensors. The sensory tag is mounted on a swimming crab (Portunus pelagicus) and is capable of continuous logging of depth, temperature, and salinity within the harsh ocean environment. The fully packaged, ultra-lightweight (<2.4 g in water), and compliant “Marine Skin” system does not have any wired connection enabling safe and weightless cutting-edge approach to monitor and assess marine life and the ecosystem’s health to support conservation and management of marine ecosystems.

    更新日期:2018-05-03
  • Anion-induced N-doping of naphthalenediimide polymer semiconductor in organic thin-film transistors
    npj Flex. Electron. Pub Date : 2018-04-16
    Yang Han, Zhuping Fei, Yen-Hung Lin, Jaime Martin, Floriana Tuna, Thomas D. Anthopoulos, Martin Heeney

    Molecular doping is an important strategy to improve the charge transport properties of organic semiconductors in various electronic devices. Compared to p-type dopants, the development of n-type dopants is especially challenging due to poor dopant stability against atmospheric conditions. In this article, we report the n-doping of the milestone naphthalenediimide-based conjugated polymer P(NDI2OD-T2) in organic thin film transistor devices by soluble anion dopants. The addition of the dopants resulted in the formation of stable radical anions in thin films, as confirmed by EPR spectroscopy. By tuning the dopant concentration via simple solution mixing, the transistor parameters could be readily controlled. Hence the contact resistance between the electrodes and the semiconducting polymer could be significantly reduced, which resulted in the transistor behaviour approaching the desirable gate voltage-independent model. Reduced hysteresis was also observed, thanks to the trap filling by the dopant. Under optimal doping concentrations the channel on-current was increased several fold whilst the on/off ratio was simultaneously increased by around one order of magnitude. Hence doping with soluble organic salts appears to be a promising route to improve the charge transport properties of n-type organic semiconductors.

    更新日期:2018-04-16
  • Flexible quantum dot light-emitting diodes for next-generation displays
    npj Flex. Electron. Pub Date : 2018-04-05
    Moon Kee Choi, Jiwoong Yang, Taeghwan Hyeon, Dae-Hyeong Kim

    In the future electronics, all device components will be connected wirelessly to displays that serve as information input and/or output ports. There is a growing demand of flexible and wearable displays, therefore, for information input/output of the next-generation consumer electronics. Among many kinds of light-emitting devices for these next-generation displays, quantum dot light-emitting diodes (QLEDs) exhibit unique advantages, such as wide color gamut, high color purity, high brightness with low turn-on voltage, and ultrathin form factor. Here, we review the recent progress on flexible QLEDs for the next-generation displays. First, the recent technological advances in device structure engineering, quantum-dot synthesis, and high-resolution full-color patterning are summarized. Then, the various device applications based on cutting-edge quantum dot technologies are described, including flexible white QLEDs, wearable QLEDs, and flexible transparent QLEDs. Finally, we showcase the integration of flexible QLEDs with wearable sensors, micro-controllers, and wireless communication units for the next-generation wearable electronics.

    更新日期:2018-04-07
Some contents have been Reproduced with permission of the American Chemical Society.
Some contents have been Reproduced by permission of The Royal Society of Chemistry.
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