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  • 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.

  • 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.

  • 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.

  • 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.

  • 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%.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

  • 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.

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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