CONSPECTUS: Infrared photodetectors are essential to many applications, including surveillance, communications, process monitoring, and biological imaging. The short-wave infrared (SWIR) spectral region (λ = 1−3 μm) is particularly powerful for health monitoring and medical diagnostics because biological tissues show low absorbance and minimal SWIR autofluorescence, enabling greater penetration depth and improved resolution in comparison with visible light. However, current SWIR photodetection technologies are largely based on epitaxially grown inorganic semiconductors, which are costly, require complex processing, and impose cooling requirements incompatible with wearable electronics. Solution-processable semiconductors are being developed for infrared detectors to enable low-cost direct deposition and facilitate monolithic integration and resolution not achievable using current technologies. In particular, organic semiconductors offer numerous advantages, including large-area and conformal coverage, temperature insensitivity, and biocompatibility, for enabling ubiquitous SWIR optoelectronics. This Account introduces recent efforts to advance the spectral response of organic photodetectors into the SWIR. High-performance visible to near-infrared (NIR) organic photodetectors have been demonstrated by leveraging the wealth of knowledge from organic solar cell research in the past decade. On the other hand, organic semiconductors that absorb in the SWIR are just emerging, and only a few organic materials have been reported that exhibit photocurrent past 1 μm. In this Account, we survey novel SWIR molecules and polymers and discuss the main bottlenecks associated with charge recombination and trapping, which are more challenging to address in narrow-band-gap photodetectors in comparison with devices operating in the visible to NIR. As we call attention to discrepancies in the literature regarding performance metrics, we share our perspective on potential pitfalls that may lead to overestimated values, with particular attention to the detectivity (signal-to-noise ratio) and temporal characteristics, in order to ensure a fair comparison of device performance. As progress is made toward overcoming challenges associated with losses due to recombination and increasing noise at progressively narrower band gaps, the performance of organic SWIR photodetectors is steadily rising, with detectivity exceeding 10 11 Jones, comparable to that of commercial germanium photodiodes. Organic SWIR photodetectors can be incorporated into wearable physiological monitors and SWIR spectroscopic imagers that enable compositional analysis. A wide range of potential applications include food and water quality monitoring, medical and biological studies, industrial process inspection, and environmental surveillance. There are exciting opportunities for low-cost organic SWIR technologies to be as widely deployable and affordable as today's ubiquitous cell phone cameras operating in the visible, which will serve as an empowering tool for users to...

This work examines an additive approach that increases dielectric screening to overcome performance challenges in organic shortwave infrared (SWIR) photodiodes. The role of the high-permittivity additive, camphoric anhydride, in the exciton dissociation and charge collection processes is revealed through measurements of transient photoconductivity and electrochemical impedance. Dielectric screening reduces the exciton binding energy to increase exciton dissociation efficiency and lowers trap-assisted recombination loss, in the absence of any morphological changes for two polymer variants. In the best devices, the peak internal quantum efficiency at 1100 nm is increased up to 66%, and the photoresponse extends to 1400 nm. The SWIR photodiodes are integrated into a 4 × 4 pixel imager to demonstrate tissue differentiation and estimate the fat-to-muscle ratio through noninvasive spectroscopic analysis.

simulation training, communication, and immersive entertainment. Yet, the utility of haptics is currently limited; moreover, it is challenging to produce the large-area, distributed signals required to mimic natural touch.It would be desirable for haptic actuators to generate large ranges of forces and displacements over short time scales, in a compact form factor in the case of wearable haptics. This dynamism is required because the structures such as the skin and elements of the musculoskeletal system are highly stretchable. Moreover, they are teeming with mechanosensory neurons that can perceive sub-micron surface features and macroscale displacements, with reaction times in milliseconds. [3,5] Thus, to accommodate this dynamism and sensitivity, an exceptionally versatile suite of materials and tools is required to realize the entire range of haptic perception.Haptic perception can be divided into two parts: the tactile and kinesthetic senses. [6][7][8] The tactile sense involves the nerve endings in the skin to detect contact, texture, and vibration. The kinesthetic sense is the awareness of the body position and involves structures located in the musculoskeletal system to sense force and motion. For example, to emulate the feeling of grasping a cup, a haptic system would need to trigger both tactile and kinesthetic senses. That is, pressure would be applied on the fingers to indicate contact, and other actuators located at the joints of the fingers would stiffen to produce resistance against moving into the space occupied by the cup. In comparison to visual or auditory inputs aiming at localized organs of eyes and ears, haptic systems require distributed inputs covering the body. The complexity involved to simulate haptic signals over large area, with sufficient spatial and temporal resolution and high dynamic range, has been a considerable challenge and thus presents exciting research opportunities.Conventional micro-electromechanical system (MEMS) has been used to implement vibrational feedback, which is the most common type of haptic effect in commercial devices today. However, fabrication techniques for MEMS are catered toward micrometer length scales and hence research is still needed to scale up MEMS assembly [9,10] for large, customized human interfaces. To realize many other promising haptic modalities, new materials and processing technologies are being explored to make devices that improve haptic realism and scalability for mass manufacturing.Haptic actuators generate touch sensations and provide realism and depth in human-machine interactions. A new generation of soft haptic interfaces is desired to produce the distributed signals over large areas that are required to mimic natural touch interactions. One promising approach is to combine the advantages of organic actuator materials and additive printing technologies. This powerful combination can lead to devices that are ergonomic, readily customizable, and economical for researchers to explore potential benefits and create new haptic applications...

An inkjet-printed inductor-capacitor (LC) resonator is demonstrated for wireless monitoring of pressure in aqueous environments. The sensing mechanism is based on a compressible capacitor that modulates the LC circuit resonant frequency depending on the applied pressure. The trace conductivity and geometric designs of inductors are improved to increase mutual inductive coupling between the sensor and the readout coil. The dielectric porosity in the capacitive sensors are tuned to enhance pressure sensitivity. The encapsulated sensor showed a linear response to pressure between 30 and 170 mmHg (4-23 kPa) with respect to atmospheric pressure and a resolution of 3 mmHg. The sensor temporal response is up to 6 Hz and capable of capturing typical heart-pulse waveforms as a proof-of-concept demonstration.

A biomimetic strategy of combining soft actuators with an exoskeleton is applied to create untethered, self‐sustained robots with high load capacity, applicable for transportation in unsupervised environments. The soft actuation components are based on liquid crystal elastomers formed into functionally graded structures by extrusion printing, which enables a high free strain of 45.5%. The robot design includes a self‐sustained oscillation mechanism incorporating a novel, highly elastic spring for energy storage and impulse release. The arthropod‐inspired exoskeleton structures are printed from polycarbonate with high strength to increase the load‐carrying capacity, or to increase moving speed by a lever mechanism that amplifies the stepping distance up to eight times. The robot achieves self‐sustained locomotion, harvesting constant infrared radiation for continual power. Leveraging the strength of the exoskeleton and the high stress of the actuator, the robot transports a load 22 times its body weight. It is capable of climbing up a slope of 40° and moving up to a quarter of its body length per minute with peripheral lever legs. The robot operation does not require external signaling controls or complex electronics, demonstrating the potential of this battery‐free, scalable, environment‐powered design with an unlimited range free from tethering constraints.