Thermal Localization Enhanced Fast Photothermoelectric Response in a Quasi-One-Dimensional Flexible NbS3 Photodetector

Lattice-guided assembly of optoelectronically active π-conjugated peptides on 1D van der Waals single crystals

The deployment of organic molecules in high-performance devices strongly relies on the formation of well-ordered domains, which is often complicated by the dynamic and sensitive nature of supramolecular interactions. Here, we engineered the assembly of water-processable, optoelectronic π-conjugated peptides into well-defined organic-inorganic heterointerfaced assemblies by leveraging the long-range anisotropic ordering of 1D van der Waals (vdW) crystals composed of subnanometer-thick transition metal sulfide chains (MS3; M = Nb, Ta) as assembly templates. We found that the monomers can readily form 1D supramolecular assemblies onto the underlying crystal surface, owing to the structural correspondence between the π-π interactions of the quaterthiophene (4T)-based peptide units (DDD-4T) and sulfur atom ordering along the NbS3 (100) surface. The heterointerfaced assemblies exhibited substantially red-shifted photoluminescence and enhanced visible-range photocurrent generation compared to solution-assembled films. Our results underscore the role of lattice matching in forming ordered supramolecular assemblies, offering an emergent approach to assembling organic building blocks endowed with improved physical properties.

Recent Advances in Broadband Photodetectors from Infrared to Terahertz

The growing need for the multiband photodetection of a single scene has promoted the development of both multispectral coupling and broadband detection technologies. Photodetectors operating across the infrared (IR) to terahertz (THz) regions have many applications such as in optical communications, sensing imaging, material identification, and biomedical detection. In this review, we present a comprehensive overview of the latest advances in broadband photodetectors operating in the infrared to terahertz range, highlighting their classification, operating principles, and performance characteristics. We discuss the challenges faced in achieving broadband detection and summarize various strategies employed to extend the spectral response of photodetectors. Lastly, we conclude by outlining future research directions in the field of broadband photodetection, including the utilization of novel materials, artificial microstructure, and integration schemes to overcome current limitations. These innovative methodologies have the potential to achieve high-performance, ultra-broadband photodetectors.

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

Artificial skin, endowed with the capability to perceive thermal stimuli without physical contact, will bring innovative interactive experiences into smart robotics and augmented reality. The implementation of touchless thermosensation, responding to both hot and cold stimuli, relies on the construction of a flexible infrared detector operating in the long-wavelength infrared range to capture the spontaneous thermal radiation. This imposes rigorous requirements on the photodetection performance and mechanical flexibility of the detector. Herein, a flexible and wearable infrared detector is presented, on basis of the photothermoelectric coupling of the tellurium-based thermoelectric multilayer film and the infrared-absorbing polyimide substrate. By suppressing the optical reflection loss and aligning the destructive interference position with the absorption peak of polyimide, the fabricated thermopile detector exhibits high sensitivity to the thermal radiation over a broad source temperature range from -50 to 110 °C, even capable of resolving 0.05 °C temperature change. Spatially resolved radiation distribution sensing is also achieved by constructing an integrated thermopile array. Furthermore, an established temperature prewarning system is demonstrated for soft robotic gripper, enabling the identification of noxious thermal stimuli in a contactless manner. A feasible strategy is offered here to integrate the infrared detection technique into the sensory modality of electronic skin.

High-Performance Flexible Broadband Photothermoelectric Photodetectors Based on Tellurium Films

Mid- and far-infrared photodetectors that can operate at room temperature are essential for both civil and military applications. However, the widespread use of mid-to-far-infrared photonic technology faces challenges due to the need for low-temperature cooling of existing commercial semiconductors and the limited optical absorption efficiency of two-dimensional materials. We have utilized the photothermoelectric effect to fabricate a self-powered, broadband, and high-performance photodetector based on a one-dimensional tellurium nanorod array film. The device surpasses energy band gap limitations, functioning even at wavelengths up to approximately 10,600 nm. In particular, the detectivity of the device can reach 4.8 × 109 Jones at 4060 nm under room-temperature conditions, which is an order of magnitude higher than that of commercially available photodetectors. It demonstrates fast response and recovery times of 8.3 and 8.8 ms. Furthermore, the device demonstrates outstanding flexibility withstanding over 300 bending cycles and environmental stability. These results suggest a viable approach for designing and developing high-performance, room-temperature, wearable optoelectronic devices.

Research Process on Photodetectors based on Group-10 Transition Metal Dichalcogenides

Rapidly evolving group-10 transition metal dichalcogenides (TMDCs) offer remarkable electronic, optical, and mechanical properties, making them promising candidates for advanced optoelectronic applications. Compared to most TMDCs semiconductors, group-10-TMDCs possess unique structures, narrow bandgap, and influential physical properties that motivate the development of broadband photodetectors, specifically infrared photodetectors. This review presents the latest developments in the fabrication of broadband photodetectors based on conventional 2D TMDCs. It mainly focuses on the recent developments in group-10 TMDCs from the perspective of the lattice structure and synthesis techniques. Recent progress in group-10 TMDCs and their heterostructures with different dimensionality of materials-based broadband photodetectors is provided. Moreover, this review accounts for the latest applications of group-10 TMDCs in the fields of nanoelectronics and optoelectronics. Finally, conclusions and outlooks are summarized to provide perspectives for next-generation broadband photodetectors based on group-10 TMDCs.

System design of large-area vertical photothermoelectric detectors based on carbon nanotube forests with MXene electrodes

Photothermoelectric (PTE) detectors that combine photothermal and thermoelectric conversion have emerged in recent years. They can overcome bandgap limitations and achieve effective infrared detection. However, the development of PTE detectors and the related system design are in the early phases. Herein, we present vertical PTE detectors utilizing the active layer of carbon nanotube forests with MXenes acting as top electrodes. The detector demonstrates its capacity for sensitive infrared detection and rapid infrared response. We also investigated the relationship between photoresponse and different MXene electrode types as well as their thickness, which guides the PTE detector configuration design. Furthermore, we packed the PTE detectors with a polytetrafluoroethylene (PTFE, Teflon) cavity. The photoresponse is improved and the degradation is significantly delayed. We also applied this PTE detector system for non-destructive tracking (NDT) applications, where the photovoltage mapping pattern proves the viability of the imaging track. This work paves the way toward infrared energy harvesters and customized industrial NDT measurement.

Quasi-One-Dimensional van der Waals Transition Metal Trichalcogenides

The transition metal trichalcogenides (TMTCs) are quasi-one-dimensional (1D) MX3-type van der Waals layered semiconductors, where M is a transition metal element of groups IV and V, and X indicates chalcogen element. Due to the unique quasi-1D crystalline structures, they possess several novel electrical properties such as variable bandgaps, charge density waves, and superconductivity, and highly anisotropic optical, thermoelectric, and magnetic properties. The study of TMTCs plays an essential role in the 1D quantum materials field, enabling new opportunities in the material research dimension. Currently, tremendous progress in both materials and solid-state devices has been made, demonstrating promising applications in the realization of nanoelectronic devices. This review provides a comprehensive overview to survey the state of the art in materials, devices, and applications based on TMTCs. Firstly, the symbolic structure, current primary synthesis methods, and physical properties of TMTCs have been discussed. Secondly, examples of TMTC applications in various fields are presented, such as photodetectors, energy storage devices, catalysts, and sensors. Finally, we give an overview of the opportunities and future perspectives for the research of TMTCs, as well as the challenges in both basic research and practical applications.

Recent Progress in Development of Carbon-Nanotube-Based Photo-Thermoelectric Sensors and Their Applications in Ubiquitous Non-Destructive Inspections

The photo-thermoelectric (PTE) effect in electronic materials effectively combines photo-absorption-induced local heating and associated thermoelectric conversion for uncooled and broadband photo-detection. In particular, this work comprehensively summarizes the operating mechanism of carbon nanotube (CNT)-film-based PTE sensors and ubiquitous non-destructive inspections realized by exploiting the material properties of CNT films. Formation of heterogeneous material junctions across the CNT-film-based PTE sensors, namely photo-detection interfaces, triggers the Seebeck effect with photo-absorption-induced local heating. Typical photo-detection interfaces include a channel-electrode boundary and a junction between P-type CNTs and N-type CNTs (PN junctions). While the original CNT film channel exhibits positive Seebeck coefficient values, the material selections of the counterpart freely govern the intensity and polarity of the PTE response signals. Based on these operating mechanisms, CNT film PTE sensors demonstrate a variety of physical and chemical non-destructive inspections. The device aggregates broad multi-spectral optical information regarding the targets and reconstructs their inner composite or layered structures. Arbitrary deformations of the device are attributed to the macroscopic flexibility of the CNT films to further monitor targets from omni-directional viewing angles without blind spots. Detection of blackbody radiation from targets using the device also visualizes their behaviors and associated changes.

A polarization-sensitive photothermoelectric photodetector based on mixed-dimensional SWCNT-MoS2 heterostructures

Mixed-dimensional van der Waals (vdW) integration has been demonstrated to be effective for the modulation of the physical properties of homogeneous materials. Herein, we reported the enhancement of photothermal conversion and decrease of thermal conductivity in metallic single-walled carbon nanotube (SWCNT) films with the integration of chemical vapor deposition-grown monolayer MoS₂ films. The induced temperature gradient in SWCNT-MoS₂ hybrid films drives carrier diffusion to generate photocurrent via the photothermoelectric (PTE) effect, and a self-powered photodetector working in the visible band range from 405 to 785 nm was demonstrated. The maximum responsivity of the device increases by 6 times compared to that of the SWCNT counterpart. More importantly, the mixed-dimensional device exhibits polarization-dependent photogeneration, showing a large anisotropy ratio of 1.55. This work paves a way for developing high-performance, polarization-sensitive photodetectors by mixed-dimensional integration.

SrTiO3 /CuNi-Heterostructure-Based Thermopile for Sensitive Human Radiation Detection and Noncontact Human-Machine Interaction

Noncontact interactive technology provides an intelligent solution to mitigate public health risks from cross-infection in the era of COVID-19. The utilization of human radiation as a stimulus source is conducive to the implementation of low-power, robust noncontact human-machine interaction. However, the low radiation intensity emitted by humans puts forward a high demand for photodetection performance. Here, a SrTiO_3-x /CuNi-heterostructure-based thermopile is constructed, which features the combination of high thermoelectric performance and near-unity long-wave infrared absorption, to realize the self-powered detection of human radiation. The response level of this thermopile to human radiation is orders of magnitude higher than those of low-dimensional-materials-based photothermoelectric detectors and even commercial thermopiles. Furthermore, a touchless input device based on the thermopile array is developed, which can recognize hand gestures, numbers, and letters in real-time. This work offers a reliable strategy to integrate the spontaneous human radiation into noncontact human-machine interaction systems.

High-Performance Ultrabroadband Photodetector Based on Photothermoelectric Effect

Ultrabroadband photodetectors (PDs) working in the frequency range from the UV to THz regions of the spectrum play a crucial role in integrated multifunction photoelectric detection. Even so, a shortage of high-performance PDs has seriously restricted the overall development of this field. The present work demonstrates a high-performance, ultrabroadband PD with a composite nanostructure comprising a suspended carbon nanotube (CNT) film on which titanium and palladium are deposited. The application of titanium and palladium to the CNT film in this device provides n-doping and p-doping, respectively, and the deposited metal nanoparticles also ensure enhanced thermal localization. This device exhibits short response time, high responsivity, large linear dynamic range, and small noise equivalent power over the ultrabroadband spectrum based on a strong photothermoelectric effect. Numerical simulation results also confirm the effective doping and enhanced thermal localization in this PD resulting from the deposited metals. A theoretical analysis shows that the thermal conductivity of the composite film is no longer independent of the temperature over a wide temperature range. This work provides a simple but novel strategy for the design of high-performance ultrabroadband PDs.

Stretchable broadband photo-sensor sheets for nonsampling, source-free, and label-free chemical monitoring by simple deformable wrapping

Chemical monitoring communicates diverse environmental information from industrial and biological processes. However, promising and sustainable systems and associated inspection devices that dynamically enable on-site quality monitoring of target chemicals confined inside transformable and opaque channels are yet to be investigated. This paper designs stretchable photo-sensor patch sheets for nonsampling, source-free, and label-free on-site dynamic chemical monitoring of liquids flowing inside soft tubes via simple deformable surface wrapping. The device integrates carbon nanotube-based broadband photo-absorbent thin films with multilayer-laminated stretchable electrodes and substrates. The patterned rigid-soft structure of the proposed device provides durability and optical stability against mechanical deformations with a stretchability range of 70 to 280%, enabling shape-conformable attachments to transformable objects. The effective use of omnidirectional and transparent blackbody radiation from free-form targets themselves allows compact measurement configuration and enhances the functionality and simplicity of this scheme, while the presenting technology monitors concentrations of arbitrary water-soluble chemicals.

High-Performance, Polarization-Sensitive, Long-Wave Infrared Photodetection via Photothermoelectric Effect with Asymmetric van der Waals Contacts

Long-wavelength infrared (LWIR) photodetection is important for heat-seeking technologies, such as thermal imaging, all-weather surveillance, and missile guidance. Among various detection techniques, photothermoelectric (PTE) detectors are promising in that they can realize ultra-broadband photodetection at room temperature without an external power supply. However, their performance in terms of speed, responsivity, and noise level in the LWIR regime still needs further improvement. Here, we demonstrated a high-performance PTE photodetector based on low-symmetry palladium selenide (PdSe₂) with asymmetric van der Waals contacts. The temperature gradient induced by asymmetric van der Waals contacts even under global illumination drives carrier diffusion to produce a photovoltage via the PTE effect. A responsivity of over 13 V/W, a response time of ∼50 μs, and a noise equivalent power of less than 7 nW/Hz^1/2 are obtained in the 4.6-10.5 μm regime at room temperature. Furthermore, due to the anisotropic absorption of PdSe₂, the detector exhibits a linear polarization angle sensitive response with an anisotropy ratio of 2.06 at 4.6 μm and 1.21 at 10.5 μm, respectively. Our proposed device architecture provides an alternative strategy to design high-performance photodetectors in the LWIR regime by utilizing van der Waals layered materials.

New Type of Thermoelectric CdSSe Nanowire Chip

Facing the increasingly serious problem of environmental pollution and energy waste, the thermoelectric generator has been attracting more and more attention owing to its advantages including low cost, no pollution, and good stability. The family of thermoelectric material is constantly extended with enhanced performance. Note that nanostructuring can enhance thermoelectric performance. However, the most recent excellent material with effective thermoelectric transformation reported from bulk materials has definite benefits to the practical application compared to nanomaterials. In this work, a nanostructure integrated macroscale thermoelectric chip, that is an alloyed band gap gradient macroscale chip (1.0 cm × 2.0 cm) composed of CdSSe nanowires, has been proven as an excellent thermoelectric generator for the first time. A high Seebeck coefficient of -152.4 μV/K and the average output voltage of 10.8 mV are obtained after optimizing the electrode patterns and distance between electrodes. More interestingly, upon illumination by white light from a xenon lamp, a photo-thermoelectric output voltage is greatly elevated to 45 mV due to the high concentration of photogenerated carriers. The CdSSe thermoelectric chip also shows good repeatability and high stability with a relative error of <6%. No study on the thermoelectric performance of such an alloyed band gap gradient macroscale chip is mentioned before. The results illustrate a bright avenue to realize a type of light-modulated macroscale thermoelectric chips by nanostructure, allowing such kinds of CdSSe chips to be used to generate electric energy in the near future.

Robot-assisted, source-camera-coupled multi-view broadband imagers for ubiquitous sensing platform

Multi-functional photo-imaging garners attention towards the development of universal safety-net sensor networks. Although there are urgent needs to comprehensively address the optical information from arbitrarily structured and located targets, investigations on multi-view sensitive broadband monitoring, being independent of the operating environment, are yet to be completed. This study presents a robot-assisted, photo-source and imager implanted, multi-view stereoscopic sensitive broadband photo-monitoring platform with reflective and transmissive switchable modes. A multifaceted photo-thermoelectric device design based on flexible carbon nanotube films facilitates the prototype demonstrations of non-destructive, target-structure-independent, free-form multi-view examinations on actual three-dimensional industrial components. Further functionalisation, namely, a portable system utilising three-dimensional printing and ultraviolet processing, achieves the unification of freely attachable photo-imagers and miniature photo-sources, enabling location-independent operation. Consequently, the non-destructive unmanned, remote, high-speed, omni-directional testing of a defective aerial miniature model winding road-bridge with a robot-assisted photo-source imager built into a multi-axis movable photo-thermoelectric monitor arm is demonstrated.

The use of imager devices to supplement broadband photo-monitoring technology has enabled multi-functional sensing capability relevant to internet of things-related applications. Here, the authors report a robotassisted imager-implanted broadband photo-monitoring sensing platform.

Anisotropic quasi-one-dimensional layered transition-metal trichalcogenides: synthesis, properties and applications

The strong in-plane anisotropy and quasi-1D electronic structures of transition-metal trichalcogenides (MX3; M = group IV or V transition metal; X = S, Se, or Te) have pronounced influence on moulding the properties of MX3 materials. In particular, the infinite trigonal MX6 prismatic chains running parallel to the b-axis are responsible for the manifestation of anisotropy in these materials. Several marvellous properties, such as inherent electronic, optical, electrical, magnetic, superconductivity, and charge density wave (CDW) transport properties, make transition-metal trichalcogenides (TMTCs) stand out from other 2D materials in the fields of nanoscience and materials science. In addition, with the assistance of pressure, temperature, and tensile strain, these materials and their exceptional properties can be tuned to a superior extent. The robust anisotropy and incommensurable properties make the MX3 family fit for accomplishing quite a lot of compelling applications in the areas of field effect transistors (FETs), solar and fuel cells, lithium-ion batteries, thermoelectricity, etc. In this review article, a precise audit of the distinctive crystal structures, static and dynamic properties, efficacious synthesis schemes, and enthralling applications of quasi-1D MX3 materials is made.