This Review summarizes recent progress in the development of polymer solar cells. It covers the scientific origins and basic properties of polymer solar cell technology, material requirements and device operation mechanisms, while also providing a synopsis of major achievements in the field over the past few years. Potential future developments and the applications of this technology are also briefly discussed.

Polymer solar cells

Conventionally, engineers have employed rigid materials to fabricate precise, predictable robotic systems, which are easily modelled as rigid members connected at discrete joints. Natural systems, however, often match or exceed the performance of robotic systems with deformable bodies. Cephalopods, for example, achieve amazing feats of manipulation and locomotion without a skeleton; even vertebrates such as humans achieve dynamic gaits by storing elastic energy in their compliant bones and soft tissues. Inspired by nature, engineers have begun to explore the design and control of soft-bodied robots composed of compliant materials. This Review discusses recent developments in the emerging field of soft robotics.

/pdf/design-fabrication-and-control-of-soft-robots-51z07seyl1.pdf

Design, fabrication and control of soft robots

Wearable sensor technologies are essential to the realization of personalized medicine through continuously monitoring an individual's state of health. Sampling human sweat, which is rich in physiological information, could enable non-invasive monitoring. Previously reported sweat-based and other non-invasive biosensors either can only monitor a single analyte at a time or lack on-site signal processing circuitry and sensor calibration mechanisms for accurate analysis of the physiological state. Given the complexity of sweat secretion, simultaneous and multiplexed screening of target biomarkers is critical and requires full system integration to ensure the accuracy of measurements. Here we present a mechanically flexible and fully integrated (that is, no external analysis is needed) sensor array for multiplexed in situ perspiration analysis, which simultaneously and selectively measures sweat metabolites (such as glucose and lactate) and electrolytes (such as sodium and potassium ions), as well as the skin temperature (to calibrate the response of the sensors). Our work bridges the technological gap between signal transduction, conditioning (amplification and filtering), processing and wireless transmission in wearable biosensors by merging plastic-based sensors that interface with the skin with silicon integrated circuits consolidated on a flexible circuit board for complex signal processing. This application could not have been realized using either of these technologies alone owing to their respective inherent limitations. The wearable system is used to measure the detailed sweat profile of human subjects engaged in prolonged indoor and outdoor physical activities, and to make a real-time assessment of the physiological state of the subjects. This platform enables a wide range of personalized diagnostic and physiological monitoring applications.

/pdf/fully-integrated-wearable-sensor-arrays-for-multiplexed-in-4nphg673vl.pdf

Fully integrated wearable sensor arrays for multiplexed in situ perspiration analysis

Since the discovery of highly conducting polyacetylene by Shirakawa, MacDiarmid, and Heeger in 1977, π-conjugated systems have attracted much attention as futuristic materials for the development and production of the next generation of electronics, that is, organic electronics. Conceptually, organic electronics are quite different from conventional inorganic solid state electronics because the structural versatility of organic semiconductors allows for the incorporation of functionality by molecular design. This versatility leads to a new era in the design of electronic devices. To date, the great number of π-conjugated semiconducting materials that have either been discovered or synthesized generate an exciting library of π-conjugated systems for use in organic electronics. 11 However, some key challenges for further advancement remain: the low mobility and stability of organic semiconductors, the lack of knowledge regarding structure property relationships for understanding the fundamental chemical aspects behind the structural design, and realization of desired properties. Organic field-effect transistors (OFETs) are a kind of device consisting of an organic semiconducting layer, a gate insulator layer, and three terminals (drain, source, and gate electrodes). OFETs are not only essential building blocks for the next generation of cheap and flexible organic circuits, but they also provide an important insight into the charge transport of πconjugated systems. Therefore, they act as strong tools for the exploration of the structure property relationships of πconjugated systems, such as parameters of field-effect mobility (μ, the drift velocity of carriers under unit electric field), current on/off ratio (the ratio of the maximum on-state current to the minimum off-state current), and threshold voltage (the minimum gate voltage that is required to turn on the transistor). 17 Since the discovery of OFETs in the 1980s, they have attracted much attention. Research onOFETs includes the discovery, design, and synthesis of π-conjugated systems for OFETs, device optimization, development of applications in radio frequency identification (RFID) tags, flexible displays, electronic papers, sensors, and so forth. It is beyond the scope of this review to cover all aspects of π-conjugated systems; hence, our focus will be on the performance analysis of π-conjugated systems in OFETs. This should make it possible to extract information regarding the fundamental merit of semiconducting π-conjugated materials and capture what is needed for newmaterials and what is the synthesis orientation of newπ-conjugated systems. In fact, for a new science with many practical applications, the field of organic electronics is progressing extremely rapidly. For example, using “organic field effect transistor” or “organic field effect transistors” as the query keywords to search the Web of Science citation database, it is possible to show the distribution of papers over recent years as shown in Figure 1A. It is very clear

Semiconducting π-conjugated systems in field-effect transistors: a material odyssey of organic electronics.

Transparent films of carbon nanotubes can accommodate strains of up to 150% and demonstrate conductivities as high as 2,200 S cm−1 in the stretched state.

Skin-like pressure and strain sensors based on transparent elastic films of carbon nanotubes

Wound healing is a dynamic process with multiple phases. Rapid profiling and quantitative characterization of inflammation and infection remain challenging. We report a paper-like battery-free in situ AI-enabled multiplexed (PETAL) sensor for holistic wound assessment by leveraging deep learning algorithms. This sensor consists of a wax-printed paper panel with five colorimetric sensors for temperature, pH, trimethylamine, uric acid, and moisture. Sensor images captured by a mobile phone were analyzed by neural network–based machine learning algorithms to determine healing status. For ex situ detection via exudates collected from rat perturbed wounds and burn wounds, the PETAL sensor can classify healing versus nonhealing status with an accuracy as high as 97%. With the sensor patches attached on rat burn wound models, in situ monitoring of wound progression or severity is demonstrated. This PETAL sensor allows early warning of adverse events, which could trigger immediate clinical intervention to facilitate wound care management.

https://www.science.org/doi/pdf/10.1126/sciadv.adg6670?download=true

Battery-free and AI-enabled multiplexed sensor patches for wound monitoring

Ambipolar organic field‐effect transistors (OFETs) are promising candidates for compact organic complementary circuits. High and balanced ambipolar mobilities that facilitate high operation speed and simplifying layout designs, as well as symmetric electrodes that minimize fabrication complexity are critical integrities for state‐of‐art ambipolar OFETs. Organic single crystals with intrinsic ambipolar characteristics are ideal active layer materials because of the high molecular ordering and low density of defects, whereas the generally low electron mobility hindered their further implantation. In this work, the highly crystallized 6,13‐bis(triisopropylsilylethynyl) pentacene single crystals are employed and successfully unveiled the intrinsic high electron mobility by a facile alcohol treatment approach. The resulting ambipolar OFETs showed averaged hole and electron mobilities both higher than 1 cm2 V−1 s−1 by a single type of metal electrode. The presented ambipolar OFETs not only improved the static and dynamic performance of ambipolar OFET‐based complementary inverters and ring oscillators by showing a high voltage gain of 186 and a short stage delay time of 0.7 ms, but they also allowed one logic gate to show two logic functions and potentially benefit the design and functionalities of future OFET‐based complementary circuits as well.

Ambipolar Organic Field‐Effect Transistors and Complementary Circuits Based on Single Crystals with Alcohol Treatment

Inhomogeneous swelling of polymer films in liquid environments may find applications in soft actuators and sensors. Among them, fluoroelastomer based films bend up spontaneously once they are placed on an acetone-soaked filter paper. The stretchability and dielectric properties of a fluoroelastomer is attractive in the fields of soft actuators and sensors, making in-depth studies on and understanding of fluoroelastomer bending behaviors important. Here, we report an abnormal size-dependent bending phenomenon of rectangular fluoroelastomer films, which transform the bending direction from the long-side bending to the short-side bending as their length or width increases or the thickness decreases. By using finite element analysis and an analytical expression obtained using a bilayer model, we reveal the key role of gravity in determining the size-dependent bending behavior. In the bilayer model, an energy quantity is obtained to characterize the role of each material and geometrical parameters in determining the size-dependent bending behavior. We further construct phase diagrams to correlate the bending modes and the film sizes based on the finite element results, which are in good agreement with experimental results. These findings can be useful for the design of future swelling-based polymer actuators and sensors.

/pdf/size-dependent-bending-of-a-rectangular-polymer-film-qdo5ok2q.pdf

Benjamin C. K. Tee

Papers

Battery-free and AI-enabled multiplexed sensor patches for wound monitoring

Ambipolar Organic Field‐Effect Transistors and Complementary Circuits Based on Single Crystals with Alcohol Treatment

Size-dependent bending of a rectangular polymer film.

Implant-to-implant wireless networking with metamaterial textiles