Touchless Thermosensation Enabled by Flexible Infrared Photothermoelectric Detector for Temperature Prewarning Function of Electronic Skin

High-performance Ag2Se-based thermoelectrics for wearable electronics

Flexible thermoelectric materials and devices hold enormous potential for wearable electronics but are hindered by inadequate material properties and inefficient assembly techniques, leading to suboptimal performance. Herein, we developed a flexible thermoelectric film, comprising Ag2Se nanowires as the primary material, a nylon membrane as a flexible scaffold, and reduced graphene oxide as a conductive network, achieving a record-high room-temperature ZT of 1.28. Hot-pressed Ag2Se nanowires exhibited strong (013) orientation, enhancing carrier mobility and electrical conductivity. Dispersed reduced graphene oxide further boosts electrical conductivity and induces an energy-filtering effect, decoupling electrical conductivity and the Seebeck coefficient to achieve an impressive power factor of 37 μW cm-1 K-2 at 300 K. The high-intensity between Ag2Se and reduced graphene oxide interfaces enhance phonon scattering, effectively reducing thermal conductivity to below 0.9 W m-1 K-1 and enabling the high ZT value. The nylon membrane endowed the film with exceptional flexibility. A large-scale out-of-plane device with 100 pairs of thermoelectric legs, assembled from these films, delivers an ultrahigh normalized power density of >9.8 μW cm-2 K-2, outperforming all reported Ag2Se-based flexible devices. When applied to the human body, the device generated sufficient power to operate a thermo-hygrometer and a wristwatch, demonstrating its practical potential for wearable electronics.

Biomimetic Flexible Capacitive Sensor with Loop Electrode and Snail Tentacle Structure for Enhanced Proximity and Pressure Sensing

Flexible electronics have garnered significant attention due to their promising applications in embodied intelligence, smart interaction, and human-machine interface (HMI). In particular, flexible sensors with a detectability of proximity and pressure hold great potential in areas such as touchless control, health monitoring, and robotic perception. Here, we present a biomimetic flexible capacitive sensor, called the loop electrode bioinspired snail tentacle sensor (LEBSTS). The loop-patterned electrode layer enhances proximity sensing via the fringing field effect, while the bioinspired snail tentacle-structured polydimethylsiloxane (PDMS) dielectric layer provides high sensitivity for pressure detection. The above design significantly improves sensing performance, achieving long-range proximity detection of 140 mm, a wide pressure-detection range from 0.9 Pa to 500 kPa, a high sensitivity of 2.844 kPa-1 (0-1 kPa), and a fast response time of 87.5 ms. Moreover, the sensor demonstrates good durability, maintaining stable performance over 4500 cycles. Furthermore, the potential application of the sensor was explored, including human motion monitoring, touchless HMI, Morse code transmission via LoRa wireless communication, and pressure visualization systems. This work provides insights into the development of a high-performance and multifunctional flexible sensor, offering a promising platform for advanced intelligent sensing applications.

Noncovalent Soft Composites with Superior Thermal Conductivity and Photothermal Efficiency for Advanced Thermal Management

Soft materials with elevated thermal conductivity are highly sought after for efficient, adaptable thermal management in contemporary electronics, yet their fabrication remains challenging. We describe a soft composite created by integrating tannic acid-mediated liquid metals and graphene nanosheets into a polyurethane matrix through a noncovalent assembly approach that involves multiple interfacial supramolecular interactions. This composite demonstrates remarkable toughness (90.39 MJ m-3) and stretchability (1050% strain) alongside superior through-plane thermal conductivity (18.69 W m-1 K-1) and in-plane thermal conductivity (8.05 W m-1 K-1). Additionally, the composite features excellent broadband light absorption (>85%) and a photothermal conversion efficiency of 84%, enabling heat generation. Our findings overcome the traditional trade-off between high thermal conductivity and mechanical compliance in a single material. We anticipate that our design strategy will pave the way for advanced thermal management materials that require functional integration.

Near-Sensor Neuromorphic Computing System Based on a Thermopile Infrared Detector and a Memristor for Encrypted Visual Information Transmission

Near-sensor neuromorphic computing systems that utilize photodetectors and memristors exhibit significant promise in the domains of visual information processing, transmission, and noise reduction recognition. In comparison to conventional photodetectors operating within the visible-light spectrum, thermopile infrared detectors offer distinct advantages in terms of concealment and security. This study proposes an integrated near-sensor computing system that combines a thermoelectric infrared detector with a memristor, which demonstrates a broad detection range (100-310 °C), rapid response time for sensing infrared signals, and excellent neuromorphic computing characteristics for information processing. Besides high-accuracy recognition of handwritten digits, near-infrared visual information recognition and voice recognition for double information encryption were demonstrated in the system. This neuromorphic computing system holds considerable potential for applications in the propagation, encryption, and recognition of security information within the infrared spectrum.

Near Infrared Light-Based Non-Contact Sensing System for Robotics Applications

With the development of artificial intelligence and the Internet of Things, non-contact sensors are expected to realize complex human-computer interaction. However, current non-contact sensors are mainly limited by accuracy and stability. Herein, an intelligent infrared photothermal non-contact sensing system is developed that provides long-distance and high-accuracy non-contact sensing. A black phosphorus (BP)-based composite organogel is designed, which exhibits excellent photothermal properties and environmental stability, as the active material. This material can detect patterns created by near-infrared (NIR) light through various patterned masks monitored by an infrared thermal imager. The constructed non-contact sensing system is capable of accurately recognizing 26 letters with an impressive accuracy rate of 99.4%. Furthermore, even small size non-contact sensors can maintain high sensitivity and stability across a wide temperature range, at long working distances, and under different current intensities and dark conditions, demonstrating exceptional robustness. Combined with machine learning method, it is demonstrated that the non-contact sensing system excels in pattern recognition and human-computer interaction. These features highlight its potential applications in intelligent robotics and remote control systems.

A DMSO-modified porous organogel with breathability and degradability for wearable electronics

Wearable electronics for real-time monitoring of the physical status of the human body have been significantly developed recently. However, the substrates of wearable electronics still suffer from the challenge, including weak mechanical properties, low breathability and weak degradation capabilities. Herein, a dimethyl sulfoxide (DMSO)-modified agar organogel (DSAO) with porous microstructures has been reported as a breathable and degradable substrate for wearable electronics. The DSAO exhibits excellent mechanical properties, where the fracture strength is as high as 34.21 MPa. In addition, DSAO exhibits excellent moisture permeability due to many tiny pores inside and can be degraded in 30 days. The devices constructed on the basis of DSAO exhibit superior pressure resolution with a pressure response of 50 mN and respond well to different pressure levels and frequencies, which demonstrates potential applications in wearable healthcare monitoring and intelligent robots.

An Ultra-Thin Wearable Thermoelectric Paster Based on Structured Organic Ion Gel Electrolyte

Thermoelectric technology that utilizes thermodynamic effects to convert thermal energy into electrical energy has greatly expanded wearable health monitoring, personalized detecting, and communicating applications. Encouragingly, thermoelectric technology assisted by artificial intelligence exerts great development potential in wearable electronic devices that rely on the self-sustainable operation of human body heat. Ionic thermoelectric (i-TE) devices that possess high Seebeck coefficients and a constant and stable electrical output are expected to achieve an effective conversation of thermal energy harvesting. Herein, we developed an i-TE paster for thermal chargeable energy storage, temperature-triggered material recognition, contact/non-contact temperature detection, and photo thermoelectric conversion applications. An all-solid-state organic ionic gel electrolyte (PVDF-HFP-PEO gel) with onion epidermal cells-like structure was sandwiched between two electrodes, which take full advantage of a synergy between the Soret effect and the polymer thermal expansion effect, thus achieving the enhanced ZT value up to 900% compared with the PEO-free electrolyte. The i-TE device delivers a Seebeck coefficient of 28 mV K-1, a maximum energy conversion efficiency of 1.3% in performance, and ultra-thin and skin-attachable properties in wearability, which demonstrate the great potential and application prospect of the i-TE paster in self-sustainable wearable electronics.

Emerging Thermal Detectors Based on Low-Dimensional Materials: Strategies and Progress

Thermal detectors, owing to their broadband spectral response and ambient operating temperature capabilities, represent a key technological avenue for surpassing the inherent limitations of traditional photon detectors. A fundamental trade-off exists between the thermal properties and the response performance of conventional thermosensitive materials (e.g., vanadium oxide and amorphous silicon), significantly hindering the simultaneous enhancement of device sensitivity and response speed. Recently, low-dimensional materials, with their atomically thin thickness leading to ultralow thermal capacitance and tunable thermoelectric properties, have emerged as a promising perspective for addressing these bottlenecks. Integrating low-dimensional materials with metasurfaces enables the utilization of subwavelength periodic configurations and localized electromagnetic field enhancements. This not only overcomes the limitation of low light absorption efficiency in thermal detectors based on low-dimensional materials (TDLMs) but also imparts full Stokes polarization detection capability, thus offering a paradigm shift towards multidimensional light field sensing. This review systematically elucidates the working principle and device architecture of TDLMs. Subsequently, it reviews recent research advancements in this field, delving into the unique advantages of metasurface design in terms of light localization and interfacial heat transfer optimization. Furthermore, it summarizes the cutting-edge applications of TDLMs in wideband communication, flexible sensing, and multidimensional photodetection. Finally, it analyzes the major challenges confronting TDLMs and provides an outlook on their future development prospects.

A biomass-derived multifunctional conductive coating with outstanding electromagnetic shielding and photothermal conversion properties for integrated wearable intelligent textiles and skin bioelectronics

Intelligent electronic textiles have important application value in the field of wearable electronics due to their unique structure, flexibility, and breathability. However, the currently reported electronic textiles are still challenged by issues such as their biocompatibility, photothermal conversion, and electromagnetic wave contamination. Herein, a multifunctional biomass-based conductive coating was developed using natural carboxymethyl starch (CMS), dopamine and polypyrrole (PPy) and then further employed for constructing multifunctional intelligent electronic textiles. The prepared textiles had excellent water resistance, breathability, antioxidant and antibacterial activities, electromagnetic shielding (33 dB) as well as photothermal conversion performance, and stability. Notably, the fabricated textile could be heated from room temperature to 55 °C within 10 s under infrared radiation, and then the surface temperature of the textile could be reduced to 40 °C (τs = 42.05 s) within 20 s, holding great significance for research on new wearable photothermal textiles. Furthermore, the textile was utilized as a skin strain sensor, demonstrating high sensitivity to temperature, strain, photothermal and bioelectric signals and motion detection. It could monitor the physiological signal, motion control, and body temperature change of the human body in real time, offering significant potential to be applicable to integrated wearable intelligent textiles and skin bioelectronics.

Electric-Ray-Inspired Universal Island-Bridge Structure for Transforming Nonpyroelectric Substrates into Pyroelectric Sensors

Large-area, flexible pyroelectric sensors have received increasing attention in a range of applications including electronic skin, robotics, and military. However, existing flexible pyroelectric sensors struggle to achieve both high pyroelectric performance and excellent mechanical properties simultaneously. Here, we propose a universal island-bridge percolation structure inspired by the electric organ of the electric ray that can enable flexible nonpyroelectric substrates with excellent mechanical properties to generate a pyroelectric effect. The island-bridge percolation network structure made of pyroelectric particles (island) and carboxyl-functionalized multiwalled carbon nanotubes (bridge) achieved the transmission and superposition of the pyroelectric effect through the film polarization and percolation effect. The pyroelectric sensor based on the island-bridge percolation network structure not only inherits the pyroelectric properties of the pyroelectric particles but also inherits the excellent mechanical properties of the nonpyroelectric substrates. The flexible pyroelectric sensors fabricated from polydimethylsiloxane (PDMS) substrates exhibit a good pyroelectric effect and excellent mechanical reliability even under 30% tensile rate and 5,000 tensile-retraction cycles, and those made from polyimide (PI) substrates can serve as electronic skin for robots to detect heat sources and possess infrared sensing properties with a maximum distance of 8 cm. This study provides ideas to fabricate flexible pyroelectric sensors with highly flexible and high-performance properties.

Unveiling van Hove Singularity-Boosted Photothermoelectric Response for Wearable Human-Radiation Detection

Van Hove singularity (vHs), the singularity point of density of states (DOS) in crystalline solids, is a research hotspot in emerging phenomena such as light-matter interaction, superconducting, and quantum anomalous Hall effect. Although the significance of vHs in photothermoelectric (PTE) effect has been recognized, its integral role in electron excitation and thermoelectric effect is still unclear, particularly in the mid-infrared band that suffers from Pauli blockade in semimetals. Here, we unveil the Fermi-level-modulated PTE behavior in the vicinity of vHs in carbon nanotubes, employing ionic-liquid gating. The concurrent enhancement of optical absorption and thermoelectric effect effectively improves the overall photoresponse by tens of folds at the vHs point. Generally applicable to strongly correlated systems such as metallic 1D nanomaterials and 2D Moiré systems, a quantitative correlation between PTE photodetectivity and electronic DOS is derived in the vicinity of the vHs point. Finally, chemically doped PTE mid-infrared detectors with graded doping levels are demonstrated to exhibit human-radiation sensitivity, high flexibility, and high transparency, paving the way for wearable sensor networks in healthcare systems and the Internet of Things.