Showing papers by "Yang Yang published in 2017"

Polymer-modified halide perovskite films for efficient and stable planar heterojunction solar cells

Abstract: The solution processing of polycrystalline perovskite films introduces trap states that can adversely affect their optoelectronic properties. Motivated by the use of small-molecule surfactants to improve the optoelectronic performance of perovskites, we demonstrate the use of polymers with coordinating groups to improve the performance of solution-processed semiconductor films. The use of these polymer modifiers results in a marked change in the electronic properties of the films, as measured by both carrier dynamics and overall device performance. The devices grown with the polymer poly(4-vinylpyridine) (PVP) show significantly enhanced power conversion efficiency from 16.9 ± 0.7% to 18.8 ± 0.8% (champion efficiency, 20.2%) from a reverse scan and stabilized champion efficiency from 17.5 to 19.1% [under a bias of 0.94 V and AM (air mass) 1.5-G, 1-sun illumination over 30 min] compared to controls without any passivation. Treating the perovskite film with PVP enables a VOC of up to 1.16 V, which is among the best reported for a CH3NH3PbI3 perovskite solar cell and one of the lowest voltage deficits reported for any perovskite to date. In addition, perovskite solar cells treated with PVP show a long shelf lifetime of up to 90 days (retaining 85% of the initial efficiency) and increased by a factor of more than 20 compared to those without any polymer (degrading to 85% after ~4 days). Our work opens up a new class of chemical additives for improving perovskite performance and should pave the way toward improving perovskite solar cells for high efficiency and stability.

Make perovskite solar cells stable.

Abstract: still expensive to process, their manufacture produces toxic by-products and they are cumbersome to install. Perovskites could be a game-changer. These materials have crystal structures that are based on pyramid-like tetrahedral arrangements of atoms or molecules. Long explored as potential semiconductors, superconductors and for their optical and magnetic properties, perovskites are also efficient at absorbing light and transporting charges — ideal properties for capturing solar power. Perovskite photovoltaic cells are cheap and easy to assemble. Typically they combine common inorganic and organic components, often methylammonium or formamidinium, both compounds of carbon, hydrogen and nitrogen. In solution, they can be printed on glass or film over several square centimetres. They are also less sensitive to impurities than are expensive crystalline semiconductors such as gallium arsenide. In the past decade, research into perovskite solar cells has boomed. At least in the lab, the efficiency of perovskite devices is now more than a match for those based on silicon (see ‘Rising performance’). In 2006, the first perovskite photovoltaic converted 2.2% of photons into electrons; by 2016, that figure was 22.1%. Silicon rooftop panels have an efficiency of 16–20%; perovskite cells could in theory could reach 31%. And even higher efficiencies might be achieved by combining silicon and perovskite devices. But there are major challenges to using perovskites on a commercial scale. The main one is stability: the cells currently only last for months outdoors, whereas silicon solar panels are usually guaranteed to work for at least 25 years. Weather changes and extreme light levels, temperature and humidity all cause perovskite cells to decompose. Moisture is the worst problem. Reactions with water form hydrates that alter the structures of the crystals so that they cannot absorb visible light. In the past decade, cell lifetimes have extended from a few minutes to 6 months. But much more work is needed. Here we highlight five ways to improve the stability of perovskite solar cells. We believe that within two years, they could exceed efficiencies of 25%, while remaining stable for more than a year.

Low-bandgap conjugated polymers enabling solution-processable tandem solar cells

Abstract: The technology of polymer-based organic photovoltaic (OPV) cells has made great progress in the past decade, with the power conversion efficiency increasing from just a few per cent to around 12%, and the stability increasing from hours to years. One of the important milestones in this progress has been the invention of infrared-absorbing low-bandgap polymers, which allows the OPV cells to form effective tandem structures for harvesting near-infrared energy from the solar spectrum. In this Review, we focus on the progress in low-bandgap conjugated polymers and several tandem OPV cells enabled by these low-bandgap polymers. Specifically, we cover polymer-based tandem solar cells; hybrid tandem solar cells combining polymers with hydrogenated amorphous silicon; and unconventional solar cells. For each of these technologies, we address the challenges and offer our perspectives for future development. Low-bandgap (<1.6 eV) polymers enable polymer solar cells to form effective tandem structures for harvesting near-infrared solar energy as well as reducing thermal loss. This Review summarizes recent progress and provides a perspective on various low-bandgap polymer-containing tandem solar cells; namely, pure polymer–polymer tandem, hybrid polymer–amorphous silicon tandem and unconventional perovskite–polymer tandem solar cells.

Tailoring the Interfacial Chemical Interaction for High-Efficiency Perovskite Solar Cells.

Abstract: The ionic nature of perovskite photovoltaic materials makes it easy to form various chemical interactions with different functional groups. Here, we demonstrate that interfacial chemical interactions are a critical factor in determining the optoelectronic properties of perovskite solar cells. By depositing different self-assembled monolayers (SAMs), we introduce different functional groups onto the SnO2 surface to form various chemical interactions with the perovskite layer. It is observed that the perovskite solar cell device performance shows an opposite trend to that of the energy level alignment theory, which shows that chemical interactions are the predominant factor governing the interfacial optoelectronic properties. Further analysis verifies that proper interfacial interactions can significantly reduce trap state density and facilitate the interfacial charge transfer. Through use of the 4-pyridinecarboxylic acid SAM, the resulting perovskite solar cell exhibits striking improvements to the reach t...

New Wide Band Gap Donor for Efficient Fullerene-Free All-Small-Molecule Organic Solar Cells

Abstract: A new organic small molecule, DRTB-T, that incorporates a two-dimensional trialkylthienyl-substituted benzodithiophene core building block was designed and synthesized. DRTB-T has a band gap (Egopt) of 2.0 eV with a low-lying highest occupied molecular orbital (HOMO) level of −5.51 eV. Nonfullerene small-molecule solar cells consisting of DRTB-T and a nonfullerene acceptor (IC-C6IDT-IC) were constructed, and the morphology of the active layer was fine-tuned by solvent vapor annealing (SVA). The device showed a record 9.08% power conversion efficiency (PCE) with a high open-circuit voltage (Voc = 0.98 V). This is the highest PCE for a nonfullerene small-molecule organic solar cell (NFSM-OSC) reported to date. Our notable results demonstrate that the molecular design of a wide band gap (WBG) donor to create a well-matched donor–acceptor pair with a low band gap (LBG) nonfullerene small-molecule acceptor, as well as subtle morphological control, provides great potential to realize high-performance NFSM-OSCs.

High-Brightness Blue and White LEDs based on Inorganic Perovskite Nanocrystals and their Composites

Abstract: Inorganic metal halide perovskite nanocrystals (NCs) have been employed universally in light-emitting applications during the past two years. Here, blue-emission (≈470 nm) Cs-based perovskite NCs are derived by directly mixing synthesized bromide and chloride nanocrystals with a weight ratio of 2:1. High-brightness blue perovskite light-emitting diodes (PeLEDs) are obtained by controlling the grain size of the perovskite films. Moreover, a white PeLED is demonstrated for the first time by blending orange polymer materials with the blue perovskite nanocrystals as the active layer. Exciton transfer from the blue nanocrystals to the orange polymers via Forster or Dexter energy transfer is analyzed through time resolved photoluminescence. By tuning the ratio between the perovskite nanocrystals and polymers, pure white light is achieved with the a CIE coordinate at (0.33,0.34).

The Interplay between Trap Density and Hysteresis in Planar Heterojunction Perovskite Solar Cells.

Abstract: Anomalous current–voltage (J–V) hysteresis in perovskite (PSK) solar cell is open to dispute, where hysteresis is argued to be due to electrode polarization, dipolar polarization, and/or native defects. However, a correlation between those factors and J–V hysteresis is hard to be directly evaluated because they usually coexist and are significantly varied depending on morphology and crystallinity of the PSK layer, selective contacts, and device architecture. In this study, without changing morphology and crystallinity of PSK layer in a planar heterojunction structure employing FA0.9Cs0.1PbI3, a correlation between J–V hysteresis and trap density is directly evaluated by means of thermally induced PbI2 regulating trap density. Increase in thermal annealing time at a given temperature of 150 °C induces growth of PbI2 on the PSK grain surface, which results in significant reduction of nonradiative recombination. Hysteresis index is reduced from 0.384 to 0.146 as the annealing time is increased from 5 to 100 ...

Multi-Frequency mmWave Massive MIMO Channel Measurements and Characterization for 5G Wireless Communication Systems

Abstract: Most millimeter wave (mmWave) channel measurements are conducted with different configurations, which may have large impacts on propagation channel characteristics. In addition, the comparison of different mmWave bands is scarce. Moreover, mmWave massive multiple-input multiple-output (MIMO) channel measurements are absent, and new propagation properties caused by large antenna arrays have rarely been studied yet. In this paper, we carry out mmWave massive MIMO channel measurements at 11-, 16-, 28-, and 38-GHz bands in indoor environments. The space-alternating generalized expectation-maximization algorithm is applied to process the measurement data. Important statistical properties, such as average power delay profile, power azimuth profile, power elevation profile, root mean square delay spread, azimuth angular spread, elevation angular spread, and their cumulative distribution functions and correlation properties, are obtained and compared for different bands. New massive MIMO propagation properties, such as spherical wavefront, cluster birth-death, and non-stationarity over the antenna array, are validated for the four mmWave bands by investigating the variations of channel parameters. Two channel models are used to verify the measurements. The results indicate that massive MIMO effects should be fully characterized for mmWave massive MIMO systems.

Carbon Quantum Dots/TiOx Electron Transport Layer Boosts Efficiency of Planar Heterojunction Perovskite Solar Cells to 19%

Abstract: In planar n-i-p heterojunction perovskite solar cells, the electron transport layer (ETL) plays important roles in charge extraction and determine the morphology of the perovskite film. Here, we report a solution-processed carbon quantum dots (CQDs)/TiO2 composite that has negligible absorption in the visible spectral range, a very attractive feature for perovskite solar cells. Using this novel CQDs/TiO2 ETL in conjunction with a planar n-i-p heterojunction, we achieved an unprecedented efficiency of ∼19% under standard illumination test conditions. It was found that a CQDs/TiO2 combination increases both the open circuit voltage and short-circuits current density as compared to using TiO2 alone. Various advanced spectroscopic characterizations including ultrafast spectroscopy, ultraviolet photoelectron spectroscopy, and electronic impedance spectroscopy elucidate that the CQDs increases the electronic coupling between the CH3NH3PbI3–xClx and TiO2 ETL interface as well as energy levers that contribute to ...

Pt-like electrocatalytic behavior of Ru–MoO2 nanocomposites for the hydrogen evolution reaction

Abstract: The design and development of inexpensive highly efficient electrocatalysts are critically important for their practical applications in the hydrogen evolution reaction (HER). Plain Ru and MoO2 are not very active for the HER under alkaline conditions. In this work, we report the preparation of Ru–MoO2 nanocomposites via a facile in situ carburization of a Ru modified Mo-based metal–organic framework. The nanocomposites exhibited very low overpotential and superior stability to achieve 10 mA cm−2 under both acidic and alkaline conditions (55 mV in 0.5 M H2SO4 and 29 mV in 1 M KOH). Their excellent performance under alkaline conditions was even better than that of 20% Pt/C. Our experimental and computational (DFT) results reveal that the remarkable activity stems from the synergistic interplay produced by strong electronic interactions between MoO2 and Ru nanoparticles. This modulated electronic structure accompanying enhanced electrical conductivity would significantly improve the catalytic activity. This strategy provides an insight into the design and synthesis of a low-cost and high performance alternative to Pt-based catalysts for the HER.

5G-Enabled Cooperative Intelligent Vehicular (5GenCIV) Framework: When Benz Meets Marconi

Abstract: As one of the most popular social media platforms today, Twitter provides people with an effective way to communicate and interact with each other Through these interactions, influence among users gradually emerges and changes people's opinions Although previous work has studied interpersonal influence as the probability of activating others during information diffusion, they ignore an important fact that information diffusion is the result of influence, while dynamic interactions among users produce influence In this article, the authors propose a novel temporal influence model to learn users' opinion behaviors regarding a specific topic by exploring how influence emerges during communications The experiments show that their model performs better than other influence models with different influence assumptions when predicting users' future opinions, especially for the users with high opinion diversity

Pure Formamidinium-Based Perovskite Light-Emitting Diodes with High Efficiency and Low Driving Voltage

Abstract: A formamidinium(FA)-based perovskite showns superior optoelectronic properties including better stability than methylammonium-based counterparts. Pure FA-perovskite-based light-emitting diodes (LEDs) with high efficiency are reported. Interestingly, the LED clearly shows a sub-bandgap emission at 1.7 V (bandgap 2.3 eV). This important discovery provides further insights of the charge transport mechanism in perovskite-based optoelectronic devices.

60-GHz Millimeter-Wave Channel Measurements and Modeling for Indoor Office Environments

Abstract: The millimeter-wave (mmWave) band will be used for the fifth-generation communication systems. In this paper, 60-GHz mmWave channel measurements and modeling are carried out for indoor office environments. The rotated directional antenna-based method and uniform virtual array-based method are adopted and compared to investigate the 60-GHz channel in a 3-D space, simultaneously covering azimuth and coelevation domains. The multipath component parameters including power, delay, azimuth, and elevation angles are estimated with the space-alternating generalized expectation–maximization estimation algorithm, and then processed with the K-means clustering algorithm. An extended Saleh–Valenzuela model with both delay and angular cluster features is used to characterize the measured channel, and the intercluster and intracluster parameters are extracted. We find that the azimuth departure angles are diverse and highly related to the antenna position and measurement environment, while the elevation departure angles are more related to the antenna height difference and confined in a relatively small direction range. The azimuth angle spread is much larger than the elevation angle spread either in global level or in cluster level. The results agree with the studies in the literature and channel models in IEEE standards.

Dual-Band Dual-Mode Textile Antenna on PDMS Substrate for Body-Centric Communications

Abstract: A dual-band antenna for off- and on-body communications in the 2.45- and 5.8-GHz Industrial, Scientific, and Medical bands is presented. The two radiation characteristics, i.e., patch-like radiation for the off-body link and monopole-like radiation for the on-body link, are achieved by utilizing inherently generated TM $_{11}$ and TM $_{02}$ modes of a circular patch antenna. A shorting pin and two arc-shaped slots are employed to tune both modes to the desired operating frequencies. This approach allows a realization of a dual-band dual-mode antenna with a very simple structure, i.e., a single radiator with a simple feed. A further advantage of the proposed antenna is its realization using a silver fabric integrated onto a flexible polydimethylsiloxane substrate that makes it more practical for wearable applications. An experimental investigation of the antenna performance has been carried out in free space and on a semisolid human muscle equivalent phantom, which shows a robust performance against the human body loading effect. When placed on the phantom, the measured bandwidths of 84 and 247 MHz in the 2.45- and 5.8-GHz bands, respectively, are achieved with the corresponding peak gains of 4.16 and 4.34 dBi, indicating a promising candidate for body-centric communications.

Controlled synthesis of Mo-doped Ni3S2 nano-rods: an efficient and stable electro-catalyst for water splitting

Abstract: Fabrication of stable, efficient, and inexpensive bifunctional electro-catalysts for water splitting has become increasingly attractive. Herein, for the first time, the direct growth of Mo-doped Ni3S2 on Ni foams using sodium molybdate as the Mo source at different temperatures is demonstrated. Effects of temperature on the morphology and water splitting performance of Mo-doped Ni3S2 were discussed in detail. It is found that the atomic stoichiometric ratios of Mo and Ni can be controlled by the adjusting of reaction temperature, while the obtained electro-catalysts demonstrate various morphologies, capacitances and chemisorption free energies of hydrogen, which lead to different current densities and hydrogen evolution efficiencies. The electro-catalyst synthesized at 200 °C (200-SMN/NF) demonstrates the best regular morphology and electrochemical properties. When employed in oxygen evolution reactions, 200-SMN/NF demonstrates a low over-potential of 180 mV at 100 mA cm−2. Adapting it as a bifunctional electro-catalyst, a current density of 10 mA cm−2 at a very low cell voltage of 1.53 V and cycling lifespan of more than 15 h was delivered. Further results indicated elevated hydrogen evolution reaction activity, consisting of a moderate 278 mV over-potential at a 100 mA cm−2 hydrogen production current density, a small 72.9 mV dec−1 Tafel slope, and a superior current density compared to that of precious catalyst Pt/C (40%) after −0.53 V. These results underscore the fact that 200-SMN/NF is a high-performance, precious-metal-free electro-catalyst, and provide the foundation for exciting opportunities in water splitting applications.

The Emergence of the Mixed Perovskites and Their Applications as Solar Cells

Abstract: The halide perovskite (PVSK) materials (with ABX3 formulation) have emerged as “dream materials” for photovoltaic (PV) applications due to their remarkable physical properties such as high optical absorption coefficient, carrier mobility, long carrier diffusion lengths, etc. These properties have enabled the PV devices to reach higher than 20% power conversion efficiencies (PCE) in record time. The further pursuit of higher PCE and improved stability brings forth increasing interests in so-called “mixed composition” PVSK materials, consisting of partial substitution of the A, B, and/or X-sites with alternative elements/molecules of similar size. Herein, we highlight the recent advances in developing mixed PVSK for PVs and their relevant optoelectronic properties. We mainly focus on mixed PVSK materials in the form of polycrystalline thin films, but also discuss nanostructured and two-dimensional (2D) PVSK materials due to the increasing interest of broad readership. Efforts are exerted to elucidate the design principles of mixed PVSK and fabrication techniques for high performance optoelectronic devices, which help deepen our fundamental understanding of mixed PVSK systems. We hope this review will shed light onto the design and synthesis of mixed PVSK materials to further the progress of PVSK photovoltaics towards higher efficiencies and longer lifetimes.

Controlled Electrodeposition Synthesis of Co–Ni–P Film as a Flexible and Inexpensive Electrode for Efficient Overall Water Splitting

Abstract: Synthesis of highly efficient and robust catalysts with earth-abundant resources for overall water splitting is essential for large-scale energy conversion processes. Herein, a series of highly active and inexpensive Co–Ni–P films were fabricated by a one-step constant current density electrodeposition method. These films were demonstrated to be efficient bifunctional catalysts for both H2 and O2 evolution reactions (HER and OER), while deposition time was deemed to be the crucial factor governing electrochemical performance. At the optimal deposition time, the obtained Co–Ni–P-2 catalyst performed remarkably for both HER and OER in alkaline media. In particular, it requires −103 mV overpotential for HER and 340 mV for OER to achieve the current density of 10 mA cm–2, with corresponding Tafel slopes of 33 and 67 mV dec–1. Moreover, it outperforms the Pt/C//RuO2 catalyst and only needs −160 mV (430 mV) overpotential for HER (OER) to achieve 200 mA cm–2 current density. Co–Ni–P electrodes were also conducte...

Substrate Integrated Waveguide Cavity-Backed Slot Array Antenna Using High-Order Radiation Modes for Dual-Band Applications in $K$ -Band

Abstract: A novel compact dual-band cavity-backed substrate integrated waveguide (SIW) array antenna using high-order radiation modes has been proposed in this paper. The first high-order hybrid mode (superposition of TM310 and TM130) and the second high-order mode (TM320) of K-band in the SIW cavity are excited by an inductive window for dual-band application. The operation mechanism of high-order modes is analyzed and then verified through simulations by inserting metallic vias in different positions of the resonant SIW cavity. The designed subarray antenna has the advantages of high gain, high front-to-back ratio, and low cross-polarization level. To further validate the design idea, a dual-frequency band $2 \times 2$ array antenna has been fabricated and measured including reflection coefficients, realized gains, and radiation patterns. The measured results show that the 10-dB impedance bandwidths at resonant frequencies of 21 and 26 GHz are 800 MHz (3.7%) and 700 MHz (2.6%), and the realized gains at boresight direction are around 16 and 17.4 dBi, respectively. Moreover, the proposed array antenna also possesses both advantages of metallic cavity-backed antennas and planar patch antennas, such as low cost, easy fabrication with the printed circuit board technology, and integration with other planar circuits.

Combining Energy Transfer and Optimized Morphology for Highly Efficient Ternary Polymer Solar Cells

Abstract: Aimed at achieving ideal morphology, illuminating morphology–performance relationship, and further improving the power conversion efficiency (PCE) of ternary polymer solar cells (TSCs), a ternary system is designed based on PTB7-Th:PffBT4T-2OD:PC71BM in this work. The PffBT4T-2OD owns large absorption cross section, proper energy levels, and good crystallinity, which enhances exciton generation, charge dissociation and transport and suppresses charge recombination, thus remarkably increasing the short-circuit current density (Jsc) and fill factor (FF). Finally, a notable PCE of 10.72% is obtained for the TSCs with 15% weight ratio of PffBT4T-2OD. As for the working mechanism, it confirmed the energy transfer from PffBT4T-2OD to PTB7-Th, which contributes to the improved exciton generation. And morphology characterization indicates that the devices with 15% PffBT4T-2OD possess both appropriate domain size (25 nm) and enhanced domain purity. Under this condition, it affords numerous D/A interface for exciton dissociation and good bicontinuous nanostructure for charge transport simultaneously. As a result, the device with 15% PffBT4T-2OD exhibits improved exciton generation, enhanced charge dissociation possibility, elevated hole mobility and inhibited charge recombination, leading to elevated Jsc (19.02 mA cm−2) and FF (72.62%) simultaneously. This work indicates that morphology optimization as well as energy transfer plays a significant role in improving TSC performance.

An On-Chip Bandpass Filter Using a Broadside-Coupled Meander Line Resonator With a Defected-Ground Structure

Abstract: An on-chip bandpass filter (BPF) is designed and fabricated in a 0.13- $\mu \text{m}$ SiGe (Bi)-CMOS technology. This BPF consists of a broadside-coupled meander-line resonator (BCMLR) in conjunction with a defected-ground structure (DGS). By simply grounding a BCMLR, the resonator can be converted into a BPF. Further applying a DGS to this BPF, an additional transmission zero can be generated in the high-frequency band. To understand the fundamentals of this design, an $LC$ -equivalent circuit is given for investigation of the transmission zeros and poles. The measured results show that the BPF has a center frequency at 33 GHz with a bandwidth of 18%. The minimum insertion loss is 2.6 dB, while the maximum stopband attenuation is 44 dB. The chip size, excluding the pads, is only 0.038 mm2 ( $0.126\times0.3$ mm $^{2}$ ).

Unraveling the High Open Circuit Voltage and High Performance of Integrated Perovskite/Organic Bulk-Heterojunction Solar Cells.

Abstract: We have demonstrated high-performance integrated perovskite/bulk-heterojunction (BHJ) solar cells due to the low carrier recombination velocity, high open circuit voltage (VOC), and increased light absorption ability in near-infrared (NIR) region of integrated devices. In particular, we find that the VOC of the integrated devices is dominated by (or pinned to) the perovskite cells, not the organic photovoltaic cells. A Quasi-Fermi Level Pinning Model was proposed to understand the working mechanism and the origin of the VOC of the integrated perovskite/BHJ solar cell, which following that of the perovskite solar cell and is much higher than that of the low bandgap polymer based organic BHJ solar cell. Evidence for the model was enhanced by examining the charge carrier behavior and photovoltaic behavior of the integrated devices under illumination of monochromatic light-emitting diodes at different characteristic wavelength. This finding shall pave an interesting possibility for integrated photovoltaic dev...

Quasi-Two-Dimensional Metal Oxide Semiconductors Based Ultrasensitive Potentiometric Biosensors.

Abstract: Ultrasensitive field-effect transistor-based biosensors using quasi-two-dimensional metal oxide semiconductors were demonstrated. Quasi-two-dimensional low-dimensional metal oxide semiconductors were highly sensitive to electrical perturbations at the semiconductor–bio interface and showed competitive sensitivity compared with other nanomaterial-based biosensors. Also, the solution process made our platform simple and highly reproducible, which was favorable compared with other nanobioelectronics. A quasi-two-dimensional In2O3-based pH sensor showed a small detection limit of 0.0005 pH and detected the glucose concentration at femtomolar levels. Detailed electrical characterization unveiled how the device’s parameters affect the biosensor sensitivity, and lowest detectable charge was extrapolated, which was consistent with the experimental data.

Interface Engineering of Metal Oxide Semiconductors for Biosensing Applications

Abstract: In the last decade, there has been considerable development in the area of oxide semiconductors, owing to their superior electrical properties as compared to a-Si:H, and lower cost and better uniformity over large areas as compared to poly-Si. On the other hand, multi-functional sensing systems play a significant role in building a bridge across bio/electronic interface and require advanced thin-film transistors (TFT) as sensing components and signal processing circuits. High-performance oxide TFTs are constructed based on material design, advanced processing and device architecture and provide higher sensitivity when compared with other active thin-film transistor platforms. Their versatile configurations and integration with functional materials make oxide TFT the focal point of sensing systems, including wearable and implantable electronics.