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  • 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
  • Large-area plastic nanogap electronics enabled by adhesion lithography
    npj Flex. Electron. Pub Date : 2018-06-25
    James Semple, Dimitra G. Georgiadou, Gwenhivir Wyatt-Moon, Minho Yoon, Akmaral Seitkhan, Emre Yengel, Stephan Rossbauer, Francesca Bottacchi, Martyn A. McLachlan, Donal D. C. Bradley, Thomas D. Anthopoulos

    Large-area manufacturing of flexible nanoscale electronics has long been sought by the printed electronics industry. However, the lack of a robust, reliable, high throughput and low-cost technique that is capable of delivering high-performance functional devices has hitherto hindered commercial exploitation. Herein we report on the extensive range of capabilities presented by adhesion lithography (a-Lith), an innovative patterning technique for the fabrication of coplanar nanogap electrodes with arbitrarily large aspect ratio. We use this technique to fabricate a plethora of nanoscale electronic devices based on symmetric and asymmetric coplanar electrodes separated by a nanogap < 15 nm. We show that functional devices including self-aligned-gate transistors, radio frequency diodes and rectifying circuits, multi-colour organic light-emitting nanodiodes and multilevel non-volatile memory devices, can be fabricated in a facile manner with minimum process complexity on a range of substrates. The compatibility of the formed nanogap electrodes with a wide range of solution processable semiconductors and substrate materials renders a-Lith highly attractive for the manufacturing of large-area nanoscale opto/electronics on arbitrary size and shape substrates.

    更新日期:2018-06-27
  • Highly sensitive integrated flexible tactile sensors with piezoresistive Ge 2 Sb2Te5 thin films
    npj Flex. Electron. Pub Date : 2018-06-15
    Zhiguang Wang, Cunzheng Dong, Xinjun Wang, Menghui Li, Tianxiang Nan, Xianfeng Liang, Huaihao Chen, Yuyi Wei, Haomiao Zhou, Mohsen Zaeimbashi, Syd Cash, Nian-Xiang Sun

    Flexible tactile sensor has been extensively investigated as a key component for emerging electronics applications such as robotics, wearable devices, computer hardware, and security systems. Tactile sensors based on various one-dimensional materials have been widely explored. However, precise control of the direction and distribution of these nanomaterials remains a great challenge, and it has been difficult to scale down the device. Here, we introduce highly sensitive integrated flexible tactile sensors based on uniform phase-change Ge2Sb2Te5 (GST) thin films that can scale device size down, at least, to micrometer range. Significant piezoresistive effect has been observed in GST-based sensors, showing a giant gauge factor of 338. A proof of concept 5 × 5 sensor array functioning as a touch panel has been demonstrated. Also, the flexible GST tactile sensor has been utilized for monitoring of radial artery pulse. In addition to the well-known tunable electrical and optical properties, the piezoresistive GST films provide a versatile platform for the integration of sensing, recording, and displaying functions.

    更新日期:2018-06-15
  • 360° omnidirectional, printable and transparent photodetectors for flexible optoelectronics
    npj Flex. Electron. Pub Date : 2018-06-08
    Der-Hsien Lien, Hsin-Ping Wang, Shih-Bin Chen, Yu-Chieh Chi, Chung-Lun Wu, Gong-Ru Lin, Ying-Chih Liao, Jr-Hau He

    Flexible optoelectronics that can be bent, wrapped, and stretched have attracted interest for wearable and mobile applications. In this work, we demonstrate a transparent 360° omnidirectional photodetector (PD) that can be stretched and wrapped around flexible or curved substrates. By embedding interlaced ZnO and Ag nanowires (NWs) in thermoplastic polyurethane via inkjet printing, the device featured > 75% transmittance in the visible region, showing high photoresponsivity and response time (10–30 A/W and 0.8 s, respectively). Moreover, the flexible PD performs well under deformation (only 9% decay in the photocurrent under 60% strain and 8% loss when the device is bent at a radius of 5 mm), which allows it to be readily applied on curved surfaces, such as skin or optical fibers. This study opens the door for the development of flexible optoelectronics that could be implemented in fiber optics, wearable electronics, self-powered systems, bio-signal monitors, and epidermal electronics.

    更新日期:2018-06-08
  • Multiscale nanowire-microfluidic hybrid strain sensors with high sensitivity and stretchability
    npj Flex. Electron. Pub Date : 2018-06-04
    Songjia Han, Chunrui Liu, Huihua Xu, Dongyuan Yao, Kanghong Yan, Huanliang Zheng, Hui-Jiuan Chen, Xuchun Gui, Sheng Chu, Chuan Liu

    Nanomaterials with low-dimensional morphology have been explored for enhancing the performance of strain sensors, but it remains difficult to achieve high stretchability and sensitivity simultaneously. In this work, a composite structure strain sensor based on nanomaterials and conductive liquid is designed, demonstrated, and engineered. The nanowire-microfluidic hybrid (NMH) strain sensor responds to multiscale strains from 4% to over 400%, with a high sensitivity and durability under small strain. Metal nanowires and carbon nanotubes are used to fabricate the NMH strain sensors, which simultaneously exhibit record-high average gauge factors and stretchability, far better than the conventional nanowire devices. Quantitative modeling of the electrical characteristics reveals that the effective conductivity percolation through the hybrid structures is the key to achieving high gauge factors for multiscale sensing. The sensors can operate at low voltages and are capable of responding to various mechanical deformations. When fixed on human skin, the sensors can monitor large-scale deformations (skeleton motion) and small-scale deformations (facial expressions and pulses). The sensors are also employed in multichannel, interactive electronic system for wireless control of robotics. Such demonstrations indicate the potential of the sensors as wearable detectors for human motion or as bionic ligaments in soft robotics.

    更新日期:2018-06-04
  • Energy harvesting textiles for a rainy day: woven piezoelectrics based on melt-spun PVDF microfibres with a conducting core
    npj Flex. Electron. Pub Date : 2018-03-22
    Anja Lund, Karin Rundqvist, Erik Nilsson, Liyang Yu, Bengt Hagström, Christian Müller

    Recent advances in ubiquitous low-power electronics call for the development of light-weight and flexible energy sources. The textile format is highly attractive for unobtrusive harvesting of energy from e.g., biomechanical movements. Here, we report the manufacture and characterisation of fully textile piezoelectric generators that can operate under wet conditions. We use a weaving loom to realise textile bands with yarns of melt-spun piezoelectric microfibres, that consist of a conducting core surrounded by β-phase poly(vinylidene fluoride) (PVDF), in the warp direction. The core-sheath constitution of the piezoelectric microfibres results in a—for electronic textiles—unique architecture. The inner electrode is fully shielded from the outer electrode (made up of conducting yarns that are integrated in the weft direction) which prevents shorting under wet conditions. As a result, and in contrast to other energy harvesting textiles, we are able to demonstrate piezoelectric fabrics that do not only continue to function when in contact with water, but show enhanced performance. The piezoelectric bands generate an output of several volts at strains below one percent. We show that integration into the shoulder strap of a laptop case permits the continuous generation of four microwatts of power during a brisk walk. This promising performance, combined with the fact that our solution uses scalable materials and well-established industrial manufacturing methods, opens up the possibility to develop wearable electronics that are powered by piezoelectric textiles.

    更新日期:2018-06-03
  • Ultra-thin chips for high-performance flexible electronics
    npj Flex. Electron. Pub Date : 2018-03-14
    Shoubhik Gupta, William Taube Navaraj, Leandro Lorenzelli, Ravinder Dahiya

    Flexible electronics has significantly advanced over the last few years, as devices and circuits from nanoscale structures to printed thin films have started to appear. Simultaneously, the demand for high-performance electronics has also increased because flexible and compact integrated circuits are needed to obtain fully flexible electronic systems. It is challenging to obtain flexible and compact integrated circuits as the silicon based CMOS electronics, which is currently the industry standard for high-performance, is planar and the brittle nature of silicon makes bendability difficult. For this reason, the ultra-thin chips from silicon is gaining interest. This review provides an in-depth analysis of various approaches for obtaining ultra-thin chips from rigid silicon wafer. The comprehensive study presented here includes analysis of ultra-thin chips properties such as the electrical, thermal, optical and mechanical properties, stress modelling, and packaging techniques. The underpinning advances in areas such as sensing, computing, data storage, and energy have been discussed along with several emerging applications (e.g., wearable systems, m-Health, smart cities and Internet of Things etc.) they will enable. This paper is targeted to the readers working in the field of integrated circuits on thin and bendable silicon; but it can be of broad interest to everyone working in the field of flexible electronics.

    更新日期:2018-06-03
  • Printed microelectrode arrays on soft materials: from PDMS to hydrogels
    npj Flex. Electron. Pub Date : 2018-05-24
    Nouran Adly, Sabrina Weidlich, Silke Seyock, Fabian Brings, Alexey Yakushenko, Andreas Offenhäusser, Bernhard Wolfrum

    Microelectrode arrays (MEAs) provide promising opportunities to study electrical signals in neuronal and cardiac cell networks, restore sensory function, or treat disorders of the nervous system. Nevertheless, most of the currently investigated devices rely on silicon or polymer materials, which neither physically mimic nor mechanically match the structure of living tissue, causing inflammatory response or loss of functionality. Here, we present a new method for developing soft MEAs as bioelectronic interfaces. The functional structures are directly deposited on PDMS-, agarose-, and gelatin-based substrates using ink-jet printing as a patterning tool. We demonstrate the versatility of this approach by printing high-resolution carbon MEAs on PDMS and hydrogels. The soft MEAs are used for in vitro extracellular recording of action potentials from cardiomyocyte-like HL-1 cells. Our results represent an important step toward the design of next-generation bioelectronic interfaces in a rapid prototyping approach.

    更新日期:2018-05-24
  • Controlled mechanical assembly of complex 3D mesostructures and strain sensors by tensile buckling
    npj Flex. Electron. Pub Date : 2018-05-14
    Xiaogang Guo, Xueju Wang, Dapeng Ou, Jilong Ye, Wenbo Pang, Yonggang Huang, John A. Rogers, Yihui Zhang

    Recent research establishes methods of controlled mechanical assembly as versatile routes to three-dimensional (3D) mesostructures from patterned 2D films, with demonstrated applicability to a broad range of materials (e.g., semiconductors, polymers, metals, and their combinations) and length scales (e.g., from sub-microscale to centimeter scale). Previously reported schemes use pre-stretched elastomeric substrates as assembly platforms to induce compressive buckling of 2D precursor structures, thereby enabling their controlled transformation into 3D architectures. Here, we introduce tensile buckling as a different, complementary strategy that bypasses the need for a pre-stretched platform, thereby simplifying the assembly process and opening routes to additional classes of 3D geometries unobtainable with compressive buckling. A few basic principles in mechanics serve as guidelines for the design of 2D precursor structures that achieve large out-of-plane motions and associated 3D transformations due to tensile buckling. Experimental and computational studies of nearly 20 examples demonstrate the utility of this approach in the assembly of complex 3D mesostructures with characteristic dimensions from micron to millimeter scales. The results also establish the use of nonlinear mechanics modeling as a mechanism for designing systems that yield desired 3D geometries. A strain sensor that offers visible readout and large detectable strain range through a collection of mechanically triggered electrical switches and LEDs serves as an application example.

    更新日期:2018-05-14
  • 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
  • Large-scale roll-to-roll printed, flexible and stable organic bulk heterojunction photodetector
    npj Flex. Electron. Pub Date : 2018-03-01
    Sichao Tong, Jun Yuan, Chujun Zhang, Chunhua Wang, Baoxing Liu, Jianqiang Shen, Huayan Xia, Yingping Zou, Haipeng Xie, Jia Sun, Si Xiao, Jun He, Yongli Gao, Junliang Yang

    A flexible and stable photodetector shows great potential applications in intelligent wearable devices, health monitoring, and biological sensing. The high-output fabrication of flexible and stable photodetector via the large-scale printing process would accelerate its commercialization. Herein, a high performance, flexible organic bulk heterojunction (BHJ) photodetector with good stability is designed and fabricated via a large-scale roll-to-roll (R2R) micro-gravure printing technique on polyethylene terephthalate (PET) or paper substrate, in which the organic BHJ active layer is structured with [6,6]-phenyl C61 butyric acid methyl ester (PCBM) and a donor–acceptor copolymer, i.e., employing 4,8-bis(2-ethylhexylthiophene) benzo[1,2-b;3,4-b′] dithiophene (BDTT) as the donor unit and 5,8-bis(5-thiophen-2-yl)-6,7-difluoro-2,3-bis(4-ethylhexyloxy-1-mata-luorophenyl) quinoxaline (ffQx) as the acceptor unit (PBDTT-ffQx). The PBDTT-ffQx/PCBM BHJ photodetector shows a broad photoresponse in ultraviolet and visible light, a high detectivity (D*) value up to 6.19 × 1011 Jones, and an excellent Iphoto/Idark as high as 5.6 × 102. It exhibits excellent flexibility and stability. Its performance parameters could maintain over 80% of original values after bending 10,000 cycles or exposing in ambient condition (humidity ~50%, temperature ~30 °C) for 50 days without any encapsulation. More importantly, the R2R micro-gravure printed PBDTT-ffQx/PCBM BHJ active layer is great homogeneous, and the responsivity (R) values of photodetector arrays show a very narrow distribution. The research results show that a high-performance PBDTT-ffQx/PCBM BHJ photodetector with well reliability and reproducibility can be fabricated via the R2R micro-gravure printing technique, which provides an available strategy for fabricating large-area and flexible electronic and optoelectronic devices.

    更新日期:2018-03-01
  • Polymer nanofibre composite nonwovens with metal-like electrical conductivity
    npj Flex. Electron. Pub Date : 2018-02-14
    Steffen Reich, Matthias Burgard, Markus Langner, Shaohua Jiang, Xueqin Wang, Seema Agarwal, Bin Ding, Jianyong Yu, Andreas Greiner

    Bendable and breathable polymer nanofibre nonwovens with metal-like electrical conductivity are required for lightweight electrodes and electric shielding design with applications in batteries, functional textiles, sensors, cars, aerospace, constructions, mobile phones, and medical devices. Metal-like conductivity in polymer nonwovens has not been achieved till now due to the limitation of the existing processing techniques. We show here, the metal-like electrical conductivity of 750,000 S/m in polyacrylonitrile (PAN), poly(ε-caprolactone) (PCL) nonwoven using very low content of silver nanowires (AgNW; 3.35 vol%). The key to the high conductivity was the homogenous distribution of AgNW in nonwoven made by wet-laid process using short electrospun fibre and AgNW dispersion. Above a threshold of 0.36 vol% AgNW, the conductivity of the nonwoven increased by seven orders of magnitude, which we attribute to the onset of percolation of the AgNW. Our nonwoven-AgNW composites show fast heating and cooling within a few seconds at a voltage of 1.1 V, which is in the range of portable devices. These composites are also breathable and bendable. The electrical conductivity was independent of the bending angle of the composite, which is important for applications mentioned above and would help other scientists to design new conductive materials in the future.

    更新日期:2018-02-14
  • Low-cost, μm-thick, tape-free electronic tattoo sensors with minimized motion and sweat artifacts
    npj Flex. Electron. Pub Date : 2018-02-13
    Youhua Wang, Yitao Qiu, Shideh Kabiri Ameri, Hongwoo Jang, Zhaohe Dai, YongAn Huang, Nanshu Lu

    Electronic tattoos (e-tattoos), also known as epidermal electronics, are ultra-thin and ultra-soft noninvasive but skin-conformable devices with capabilities including physiological sensing and transdermal stimulation and therapeutics. The fabrication of e-tattoos out of conventional inorganic electronic materials used to be tedious and expensive. Recently developed cut-and-paste method has significantly simplified the process and lowered the cost. However, existing cut-and-paste method entails a medical tape on which the electronic tattoo sensors should be pasted, which increases tattoo thickness and degrades its breathability. To address this problem, here we report a slightly modified cut-and-paste method to fabricate low-cost, open-mesh e-tattoos with a total thickness of just 1.5 μm. E-tattoos of such thinness can be directly pasted on human skin and conforms to natural skin texture. We demonstrate that this ultra-thin, tape-free e-tattoo can confidently measure electrocardiogram (ECG), skin temperature, and skin hydration. Heart rate and even respiratory rate can be extracted from the ECG signals. A special advantage of such ultra-thin e-tattoo is that it is capable of high-fidelity sensing with minimized motion artifacts under various body movements. Effects of perspiration are found to be insignificant due to the breathability of such e-tattoos.

    更新日期:2018-02-14
  • Asymmetric photocurrent extraction in semitransparent laminated flexible organic solar cells
    npj Flex. Electron. Pub Date : 2018-02-05
    Jonas Bergqvist, Thomas Österberg, Armantas Melianas, Luis Ever Aguirre, Zheng Tang, Wanzhu Cai, Zaifei Ma, Martijn Kemerink, Desta Gedefaw, Mats R. Andersson, Olle Inganäs

    Scalable production methods and low-cost materials with low embodied energy are key to success for organic solar cells. PEDOT(PSS) electrodes meet these criteria and allow for low-cost and all solution-processed solar cells. However, such devices are prone to shunting. In this work we introduce a roll-to-roll lamination method to construct semitransparent solar cells with a PEDOT(PSS) anode and an polyethyleneimine (PEI) modified PEDOT(PSS) cathode. We use the polymer:PCBM active layer coated on the electrodes as the lamination adhesive. Our lamination method efficiently eliminates any shunting. Extended exposure to ambient degrades the laminated devices, which manifests in a significantly reduced photocurrent extraction when the device is illuminated through the anode, despite the fact that the PEDOT(PSS) electrodes are optically equivalent. We show that degradation-induced electron traps lead to increased trap-assisted recombination at the anode side of the device. By limiting the exposure time to ambient during production, degradation is significantly reduced. We show that lamination using the active layer as the adhesive can result in device performance equal to that of conventional sequential coating.

    更新日期:2018-02-05
  • Room-temperature processing of silver submicron fiber mesh for flexible electronics
    npj Flex. Electron. Pub Date : 2018-01-25
    Xiaopeng Bai, Sen Lin, Haolun Wang, Yi Zong, Haiyang Wang, Ziyun Huang, Donglai Li, Chang Wang, Hui Wu

    Ultrathin, patterned, conducting metallic fibers have been extensively studied as building blocks in flexible electronics. However, their scalable processing and attainment of patterns at room temperature is challenging. In this paper, we report on the patterning of ultra-long silver submicron fibers as woven mesh through the process of continuous draw spinning in the presence of ultraviolet (UV) treatment. The silver fibers can be directly intertwined on flexible substrates, such as polyethylene terephthalate (PET) and polyimide (PI). The as obtained silver submicron fiber mesh present excellent photoelectric properties (T = 90%, R = 9 Ω sq−1) and outstanding flexibility and can be easily transferred on other surfaces. To demonstrate its application, flexible electrochromic smart window and infrared stealth film have been prepared.

    更新日期:2018-01-25
  • Curvy surface conformal ultra-thin transfer printed Si optoelectronic penetrating microprobe arrays
    npj Flex. Electron. Pub Date : 2018-01-18
    Kyoseung Sim, Zhoulyu Rao, Yanbin Li, Dong Yang, Cunjiang Yu

    Penetrating neural probe arrays are powerful bio-integrated devices for studying basic neuroscience and applied neurophysiology, underlying neurological disorders, and understanding and regulating animal and human behavior. This paper presents a penetrating microprobe array constructed in thin and flexible fashion, which can be seamlessly integrated with the soft curvy substances. The function of the microprobes is enabled by transfer printed ultra-thin Si optoelectronics. As a proof-of-concept device, microprobe array with Si photodetector arrays are demonstrated and their capability of mapping the photo intensity in space are illustrated. The design strategies of utilizing thin polyimide based microprobes and supporting substrate, and employing the heterogeneously integrated thin optoelectronics are keys to accomplish such a device. The experimental and theoretical investigations illustrate the materials, manufacturing, mechanical and optoelectronic aspects of the device. While this paper primarily focuses on the device platform development, the associated materials, manufacturing technologies, and device design strategy are applicable to more complex and multi-functionalities in penetrating probe array-based neural interfaces and can also find potential utilities in a wide range of bio-integrated systems.

    更新日期:2018-01-18
  • Enhanced power conversion efficiency in iridium complex-based terpolymers for polymer solar cells
    npj Flex. Electron. Pub Date : 2018-01-11
    Zhongyuan Xue, Shifan Wang, Jie Yang, Yu Zhong, Min Qian, Cheng Li, Zhiguo Zhang, Guichuan Xing, Sven Huettner, Youtian Tao, Yongfang Li, Wei Huang

    By introducing various low concentrations of Iridium complexes to the famous donor polymer of PTB7-Th backbone, new heavy metal containing terpolymers have been demonstrated. When blended with PC71BM, an obvious increase of power conversion efficiency (PCE) is obtained in 1 mol% Ir containing polymer for different photovoltaic devices either using Ca or PDIN as cathode interface layers. The impact of molecular weight on the photovoltaic performance has been particularly considered by using three batches of control polymer PTB7-Th to ensure a fair and more convincing comparison. At similar molecular weight conditions (Mn: ~60 kg mol−1, Mw: 100–110 kg mol−1), the 1 mol% Ir containing PTB7-ThIr1/PC71BM blends exhibits enhanced PCE to 9.19% compared with 7.92% of the control PTB7-Th. Through a combination of physical measurement, such as optoelectrical characterization, GIWAXS and pico-second time-resolved photoluminescence, the enhancement are contributed from comprehensive factors of higher hole mobility, less bimolecular recombination and more efficient slow process of charge separation.

    更新日期:2018-01-11
  • On the unipolarity of charge transport in methanofullerene diodes
    npj Flex. Electron. Pub Date : 2017-12-18
    Ardalan Armin, Safa Shoaee, Qianqian Lin, Paul L Burn, Paul Meredith

    Fullerenes are electron transporting organic semiconductors with a wide range of applications. In particular, methanofullerenes have been the preferred choice for solution-processed solar cells and photodiodes. The wide applicability of fullerenes as both ‘n-type’ transport materials and electron acceptors is clear. However, what is still a matter of debate is whether the fullerenes can also support efficient transport of holes, particularly in diode geometries. In this letter, we utilize a number of recently developed experimental methods for selective electron and hole mobility measurements. We show for the two most widely used solution processable fullerenes, PC70- and-PC60BM, that whilst both exhibit electron mobilities as high as 10−3 cm2/Vs, their hole mobilities are < 10−9 cm2/Vs. Thus charge transport in these fullerenes can be considered predominantly unipolar in diode configurations.

    更新日期:2017-12-18
  • Solution-based polycrystalline silicon transistors produced on a paper substrate
    npj Flex. Electron. Pub Date : 2017-12-13
    Miki Trifunovic, Paolo Maria Sberna, Tatsuya Shimoda, Ryoichi Ishihara

    Printing of electronics is pursued as a low-cost alternative to conventional manufacturing processes. In addition, owing to relatively low process temperatures, flexible substrates can be used enabling novel applications. Among flexible substrates, paper was found to be a particularly interesting candidate, since it has an order of magnitude lower price than low-cost polymer alternatives, and is biodegradable. As ink materials, organic and metal-oxide semiconductors are thoroughly being investigated; however, they lack in electric performance compared to silicon in terms of device mobility, reliability, and energy efficiency. In recent years, liquid precursors for silicon were found and used to create polycrystalline silicon (poly-Si). However, fabrication of transistors on top of low-cost flexible substrates such as paper has remained an outstanding challenge. Here we demonstrate both p-channel and n-channel poly-Si thin-film transistors (TFTs) fabricated directly on top of paper with field-effect mobilities of 6.2 and 2.0 cm2/V s, respectively. Many fabrication challenges have been overcome by limiting the maximum process temperature to approximately 100 °C, and avoiding liquid chemicals commonly used for etching and cleaning. Patterning of poly-Si has been achieved by additive selective crystallization of the precursor film using an excimer laser. This work serves as a proof of concept, and has the potential to further improve device performance. Owing to the low-cost, biodegradable nature of paper, and the high performance, reliability, and energy efficiency of poly-Si TFTs, this work opens a pathway toward truly low-cost, low-power, recyclable applications including smart packages, biodegradable health monitoring units, flexible displays, and disposable sensor nodes.

    更新日期:2017-12-14
  • Enhanced thermal stability of organic solar cells comprising ternary D-D-A bulk-heterojunctions
    npj Flex. Electron. Pub Date : 2017-12-04
    Dominik Landerer, Adrian Mertens, Dieter Freis, Robert Droll, Tobias Leonhard, Alexander Deniz Schulz, Daniel Bahro, Alexander Colsmann

    Ternary absorber blends have recently been identified as promising concepts to spectrally broaden the absorption of organic bulk-heterojunction solar cells and hence to improve their power conversion efficiencies. In this work, we demonstrate that D-D-A ternary blends comprising two donor polymers and the acceptor PC61BM can also significantly enhance the thermal stability of the solar cell. Upon harsh thermal stress at 120 °C for 2 h, the ternary solar cells show only a minor relative deterioration of 10%. Whereas the polymer/fullerene blend PTB7-Th:PC61BM is rather unstable under these conditions, its degradation was efficiently suppressed by incorporating the near infrared-absorbing polymer PDTP–DFBT. Spectroscopic ellipsometry investigations and an effective medium analysis of the ternary absorber blend revealed that the domain conformation in presence of PDTP–DFBT remains stable whereas the domain conformation changes in its absence. The ternary PTB7-Th:PDTP–DFBT:PC61BM solar cells yield thermally stable power conversion efficiencies of up to 6%.

    更新日期:2017-12-14
  • Triboelectric nanogenerators as flexible power sources
    npj Flex. Electron. Pub Date : 2017-11-22
    Yang Wang, Ya Yang, Zhong Lin Wang

    The triboelectric nanogenerator (TENG) as a new power-generation technology was reported by Wang and co-workers in 2012. Because of its great potential for scavenging mechanical energy from living environment and sustainably driving portable devices, many researchers have developed various methods to improve output performances of TENG. In this paper, we review the progress in TENG made as flexible power sources by integrating flexible materials and stretching structures, especially for the applications of flexible electronics. For optimizing performances of TENG, the structural designs, material selections, and hybrid energy cells are presented. The reported TENG as flexible power sources has the potential applications in lighting up light emitting diodes (LEDs), powering sensors, and monitoring biomechanical motions.

    更新日期:2017-12-14
  • Research on flexible display at Ulsan National Institute of Science and Technology
    npj Flex. Electron. Pub Date : 2017-11-13
    Jihun Park, Sanghyun Heo, Kibog Park, Myoung Hoon Song, Ju-Young Kim, Gyouhyung Kyung, Rodney Scott Ruoff, Jang-Ung Park, Franklin Bien

    Displays represent information visually, so they have become the fundamental building block to visualize the data of current electronics including smartphones. Recently, electronics have been advanced toward flexible and wearable electronics that can be bent, folded, or stretched while maintaining their performance under various deformations. Here, recent advances in research to demonstrate flexible and wearable displays are reviewed. We introduce these results by dividing them into several categories according to the components of the display: active-matrix backplane, touch screen panel, light sources, integrated circuit for fingerprint touch screen panel, and characterization tests; and we also present mechanical tests in nano-meter scale and visual ergonomics research.

    更新日期:2017-12-14
  • Reconfigurable systems for multifunctional electronics
    npj Flex. Electron. Pub Date : 2017-11-02
    Jia Zhu, Michael Dexheimer, Huanyu Cheng

    Reconfigurable systems complement the existing efforts of miniaturizing integrated circuits to provide a new direction for the development of future electronics. Such systems can integrate low dimensional materials and metamaterials to enable functional transformation from the deformation to changes in multiple physical properties, including mechanical, electric, optical, and thermal. Capable of overcoming the mismatch in geometries and forms between rigid electronics and soft tissues, bio-integrated electronics enabled by reconfigurable systems can provide continuous monitoring of physiological signals. The new opportunities also extend beyond to human-computer interfaces, diagnostic/therapeutic platforms, and soft robotics. In the development of these systems, biomimicry has been a long lasting inspiration for the novel yet simple designs and technological innovations. As interdisciplinary research becomes evident in such development, collaboration across scientists and physicians from diverse backgrounds would be highly encouraged to tackle grand challenges in this field.

    更新日期:2017-12-14
  • Flexible and biocompatible high-performance solid-state micro-battery for implantable orthodontic system
    npj Flex. Electron. Pub Date : 2017-10-25
    Arwa T. Kutbee, Rabab R. Bahabry, Kholod O. Alamoudi, Mohamed T. Ghoneim, Marlon D. Cordero, Amani S. Almuslem, Abdurrahman Gumus, Elhadj M. Diallo, Joanna M. Nassar, Aftab M. Hussain, Niveen M. Khashab, Muhammad M. Hussain

    To augment the quality of our life, fully compliant personalized advanced health-care electronic system is pivotal. One of the major requirements to implement such systems is a physically flexible high-performance biocompatible energy storage (battery). However, the status-quo options do not match all of these attributes simultaneously and we also lack in an effective integration strategy to integrate them in complex architecture such as orthodontic domain in human body. Here we show, a physically complaint lithium-ion micro-battery (236 μg) with an unprecedented volumetric energy (the ratio of energy to device geometrical size) of 200 mWh/cm3 after 120 cycles of continuous operation. Our results of 90% viability test confirmed the battery’s biocompatibility. We also show seamless integration of the developed battery in an optoelectronic system embedded in a three-dimensional printed smart dental brace. We foresee the resultant orthodontic system as a personalized advanced health-care application, which could serve in faster bone regeneration and enhanced enamel health-care protection and subsequently reducing the overall health-care cost.

    更新日期:2017-12-14
  • Ultrasensitive flexible broadband photodetectors achieving pA scale dark current
    npj Flex. Electron. Pub Date : 2017-10-16
    Xiao Luo, Feiyu Zhao, Lili Du, Wenli Lv, Kun Xu, Yingquan Peng, Ying Wang, Feiping Lu

    Organolead halide perovskite is a newly emerging low-cost, solution-processable material with a broadband absorption from the ultraviolet (UV) to visible (Vis) region, which has attracted a great deal of interest in high-performance optoelectronic devices. However, some practicable applications need a cover of UV–Vis–NIR region for photoelectric conversion, a task that remains a significant challenge for further extending the absorption toward the near-infrared radiation (NIR) region. Here, to the best of our knowledge, we prove for the first time an ultrasensitive flexible broadband photodetector based on porous organolead perovskite-phthalocyanine heterostructure, which combines the synergetic properties of high UV–Vis absorbance of perovskite with enhanced NIR absorption for triclinic lead phthalocyanine. The photosensitivity of the as-prepared devices reaches up to 104 at a low intensity of 10 mW cm−2, which is among the largest values reported for broadband photodetectors. Significantly, performed at room temperature, the device achieves a pA scale dark current along with an ultrafast response speed of less than 0.6 ms for as-adopted full spectra. Our results provide an easy and promising route to develop low-cost, flexible and highly sensitive UV–Vis–NIR photodetectors.

    更新日期:2017-12-14
  • Buckling analysis in stretchable electronics
    npj Flex. Electron. Pub Date : 2017-10-05
    Bo Wang, Siyuan Bao, Sandra Vinnikova, Pravarsha Ghanta, Shuodao Wang

    In the last decade, stretchable electronics evolved as a class of novel systems that have electronic performances equal to established semiconductor technologies, but can be stretched, compressed, and twisted like a rubber band. The compliance and stretchability of these electronics allow them to conform and mount to soft, elastic biological organs and tissues, thereby providing attractive opportunities in health care and bio-sensing. Majority of stretchable electronic systems use an elastomeric substrate to carry an ultrathin circuit mesh that consists of sparsely distributed stiff, thin-film electronic components interconnected by various forms of stretchable metal strips or low-dimension materials. During the fabrication processes and application of stretchable electronics, the thin-film components or nanomaterials undergo different kinds of in-plane deformation that often leads to out-of-plane or lateral buckling, in-surface buckling, or a combination of all. A lot of creative concepts and ideas have been developed to control and harness buckling behaviors, commonly regarded as pervasive occurrences in structural designs, to facilitate fabrication of stretchable structures, or to enhance stretchability. This paper provides a brief review of recent progresses on buckling analysis in stretchable electronics. Detailed buckling mechanics reveals important correlations between the geometric/material properties and system performance (e.g., mechanical robustness, deformability, structural architecture, and control). These mechanics models and analysis provide insights to design and optimize stretchable electronics for a wide range of important applications.

    更新日期:2017-12-14
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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上海交通大学化学化工学院陈刚课题组招聘启事
南方科技大学招聘电子信息材料与器件方向博士后和研究助理教授
【问答】请问在THF、氢氧化钠的条件下,图中自由基中间体能否继续裂解?
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