Low-cost writing method for self-powered paper-based UV photodetectors utilizing Te/TiO2 and Te/ZnO heterojunctions

Spatially Resolved Light-Induced Ferroelectric Polarization in α-In2Se3/Te Heterojunctions

Light-induced ferroelectric polarization in 2D layered ferroelectric materials holds promise in photodetectors with multilevel current and reconfigurable capabilities. However, translating this potential into practical applications for high-density optoelectronic information storage remains challenging. In this work, an α-In2Se3/Te heterojunction design that demonstrates spatially resolved, multilevel, nonvolatile photoresponsivity is presented. Using photocurrent mapping, the spatially localized light-induced poling state (LIPS) is visualized in the junction region. This localized ferroelectric polarization induced by illumination enables the heterojunction to exhibit enhanced photoresponsivity. Unlike previous reports that observe multilevel polarization enhancement in electrical resistance, the device shows nonvolatile photoresponsivity enhancement under illumination. After polarization saturation, the photocurrent increases up to 1000 times, from 10-12 to 10-9 A under the irradiation of a 520 nm laser with a power of 1.69 nW, compared to the initial state in a self-driven mode. The photodetector exhibits high detectivity of 4.6×1010 Jones, with a rise time of 27 µs and a fall time of 28 µs. Furthermore, the device's localized poling characteristics and multilevel photoresponse enable spatially multiplexed optical information storage. These results advance the understanding of LIPS in 2D ferroelectric materials, paving the way for optoelectronic information storage technologies.

Versatile Papertronics: Photo-Induced Synapse and Security Applications on Papers

Paper is a readily available material in nature. Its recyclability, eco-friendliness, portability, flexibility, and affordability make it a favored substrate for researchers seeking cost-effective solutions. Electronic devices based on solution process are fabricated on paper and banknotes using PVK and SnO2 nanoparticles. The devices manufactured on paper substrates exhibit photosynaptic behavior under ultraviolet pulse illumination, stemming from numerous interactions on the surface of the SnO2 nanoparticles. A light-modulated artificial synapse device is realized on a paper at a low voltage bias of -0.01 V, with an average recognition rate of 91.7% based on the Yale Face Database. As a security device on a banknote, 400 devices in a 20 × 20 array configuration exhibited random electrical characteristics owing to the local morphology of the SnO2 nanoparticles and differences in the depletion layer width at the SnO2/PVK interface. The security Physically Unclonable Functions (PUF) key based on the current distribution extracted at -1 V show unpredictable reproducibility with 50% uniformity, 48.7% inter-Hamming distance, and 50.1% bit-aliasing rates. Moreover, the device maintained its properties for more than 210 days under a curvature radius of 8.75 mm and bias and UV irradiation stress conditions.

Electrically Tunable Multiple-Effects Synergistic and Boosted Photoelectric Performance in Te/WSe2 Mixed-Dimensional Heterojunction Phototransistors

Mix-dimensional heterojunctions (MDHJs) photodetectors (PDs) built from bulk and 2D materials are the research focus to develop hetero-integrated and multifunctional optoelectronic sensor systems. However, it is still an open issue for achieving multiple effects synergistic characteristics to boost sensitivity and enrich the prospect in artificial bionic systems. Herein, electrically tunable Te/WSe2 MDHJs phototransistors are constructed, and an ultralow dark current below 0.1 pA and a large on/off rectification ratio of 106 is achieved. Photoconductive, photovoltaic, and photo-thermoelectric conversions are simultaneously demonstrated by tuning the gate and bias. By these synergistic effects, responsivity and detectivity respectively reach 13.9 A W-1 and 1.37 × 1012 Jones with 400 times increment. The Te/WSe2 MDHJs PDs can function as artificial bionic visual systems due to the comparable response time to those of the human visual system and the presence of transient positive and negative response signals. This work offers an available strategy for intelligent optoelectronic devices with hetero-integration and multifunctions.

Quantum enhanced efficiency and spectral performance of paper-based flexible photodetectors functionalized with two dimensional materials

Flexible photodetectors (PDs) have exotic significance in recent years due to their enchanting potential in future optoelectronics. Moreover, paper-based fabricated PDs with outstanding flexibility unlock new avenues for future wearable electronics. Such PD has captured scientific interest for its efficient photoresponse properties due to the extraordinary assets like significant absorptive efficiency, surface morphology, material composition, affordability, bendability, and biodegradability. Quantum-confined materials harness the unique quantum-enhanced properties and hold immense promise for advancing both fundamental scientific understanding and practical implication. Two-dimensional (2D) materials as quantum materials have been one of the most extensively researched materials owing to their significant light absorption efficiency, increased carrier mobility, and tunable band gaps. In addition, 2D heterostructures can trap charge carriers at their interfaces, leading increase in photocurrent and photoconductivity. This review represents comprehensive discussion on recent developments in such PDs functionalized by 2D materials, highlighting charge transfer mechanism at their interface. This review thoroughly explains the mechanism behind the enhanced performance of quantum materials across a spectrum of figure of merits including external quantum efficiency, detectivity, spectral responsivity, optical gain, response time, and noise equivalent power. The present review studies the intricate mechanisms that reinforce these improvements, shedding light on the intricacies of quantum materials and their significant capabilities. Moreover, a detailed analysis of the technical applicability of paper-based PDs has been discussed with challenges and future trends, providing comprehensive insights into their practical usage in the field of future wearable and portable electronic technologies.

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.

Quantum tailoring for polarization-discriminating Bi2S3 nanowire photodetectors and their multiplexing optical communication and imaging applications

In this study, cost-efficient atmospheric pressure chemical vapor deposition has been successfully developed to produce well-aligned high-quality monocrystalline Bi2S3 nanowires. By virtue of surface strain-induced energy band reconstruction, the Bi2S3 photodetectors demonstrate a broadband photoresponse across 370.6 to 1310 nm. Upon a gate voltage of 30 V, the responsivity, external quantum efficiency, and detectivity reach 23 760 A W-1, 5.55 × 106%, and 3.68 × 1013 Jones, respectively. The outstanding photosensitivity is ascribed to the high-efficiency spacial separation of photocarriers, enabled by synergy of the axial built-in electric field and type-II band alignment, as well as the pronounced photogating effect. Moreover, a polarization-discriminating photoresponse has been unveiled. For the first time, the correlation between quantum confinement and dichroic ratio is systematically explored. The optoelectronic dichroism is established to be negatively correlated with the cross dimension (i.e., width and height) of the channel. Specifically, upon 405 nm illumination, the optimized dichroic ratio reaches 2.4, the highest value among the reported Bi2S3 photodetectors. In the end, proof-of-concept multiplexing optical communications and broadband lensless polarimetric imaging have been implemented by exploiting the Bi2S3 nanowire photodetectors as light-sensing functional units. This study develops a quantum tailoring strategy for tailoring the polarization properties of (quasi-)1D material photodetectors whilst depicting new horizons for the next-generation opto-electronics industry.

Annealing effect on the physical properties of TiO2 thin films deposited by spray pyrolysis

Titanium dioxide (TiO2) thin films were deposited on glass substrates at 350 °C using the spray pyrolysis technique. As deposited and annealed thin films were characterized by X-ray diffraction, scanning electron microscopy, UV-VIS spectroscopy, and photodetection. Unlike the as deposited samples which were amorphous, annealed samples show an anatase phase. Films were absorbent in the UV region and the band gap energy decreases from 3.78 eV to 3.4 eV with annealing. The photoresponse of TiO2 photodetectors was recorded under UV (λ1 = 365 nm, λ2 = 254 nm) and visible light illumination by reversible switching (ON/OFF) cycles using DC electrical characterization. Photosensitive properties such as reproducible photosensitivity, responsivity, and detectivity were also studied.

High Performance GaN-Based Ultraviolet Photodetector via Te/Metal Electrodes

Photodetectors (PDs) based on two-dimensional (2D) materials have promising applications in modern electronics and optoelectronics. However, due to the intralayer recombination of the photogenerated carriers and the inevitable surface trapping stages of the constituent layers, the PDs based on 2D materials usually suffer from low responsivity and poor response speed. In this work, a distinguished GaN-based photodetector is constructed on a sapphire substrate with Te/metal electrodes. Due to the metal-like properties of tellurium, the band bending at the interface between Te and GaN generates an inherent electric field, which greatly reduces the carrier transport barrier and promotes the photoresponse of GaN. This Te-enhanced GaN-based PD show a promising responsivity of 4951 mA/W, detectivity of 1.79 × 10¹⁴ Jones, and an external quantum efficiency of 169%. In addition, owing to the collection efficiency of carriers by this Te-GaN interface, the response time is greatly decreased compared with pure GaN PDs. This high performance can be attributed to the fact that Te reduces the contact resistance of the metal electrode Au/Ti to GaN, forming an ohmic-like contact and promoting the photoresponse of GaN. This work greatly extends the application potential of GaN in the field of high-performance photodetectors and puts forward a new way of developing high performance photodetectors.

A two-dimensional Te/ReS2 van der Waals heterostructure photodetector with high photoresponsivity and fast photoresponse

Two-dimensional (2D) semiconductors are the building blocks for high-performance optoelectronic devices. However, the performance of photoconductive photodetectors based on 2D semiconductors is hampered by low photoresponsivity and large dark current. Herein, a van der Waals heterostructure (vdWH) composed of rhenium disulfide (ReS₂) and tellurium (Te) is fabricated. The Te/ReS₂ vdWH photodetector exhibits a sensitive and broadband photoresponse and has high photoresponse on/off ratios under ultraviolet and visible light illumination, especially over 10² in visible light. The Te/ReS₂ vdWH photodetector achieves the responsivity of 7.9 A W^-1 at 365 nm, 3.02 A W^-1 at 450 nm, 2.37 A W^-1 at 532 nm, and 2.45 A W^-1 at 660 nm. In addition, the device achieves a high specific detectivity of 10¹¹ Jones and a fast photoresponse speed of 11.9 μs. Such high responsivity could be attributed to the efficient absorption of phonons by the Te/ReS₂ vdWH and the high-quality heterostructure interfaces with a small amount of trap states. The highly crystalline structure of Te/ReS₂ with a low density of defects reduces the grain boundary scattering, leading to the rapid diffusion of charge carriers. Moreover, the Te/ReS₂ vdWH device exhibits a photovoltaic effect and can be employed as a self-powered photodetector (SPPD), which is sensitive to visible light of 450 nm, 532 nm, and 660 nm. Our findings demonstrate that the Te/ReS₂ vdWH photodetector is an ideal building block for the next-generation electronic and optoelectronic devices in practical applications.

Emerging Trends in 2D TMDs Photodetectors and Piezo-Phototronic Devices

The piezo-phototronic effect shows promise with regards to improving the performance of 2D semiconductor-based flexible optoelectronics, which will potentially open up new opportunities in the electronics field. Mechanical exfoliation and chemical vapor deposition (CVD) influence the piezo-phototronic effect on a transparent, ultrasensitive, and flexible van der Waals (vdW) heterostructure, which allows the use of intrinsic semiconductors, such as 2D transition metal dichalcogenides (TMD). The latest and most promising 2D TMD-based photodetectors and piezo-phototronic devices are discussed in this review article. As a result, it is possible to make flexible piezo-phototronic photodetectors, self-powered sensors, and higher strain tolerance wearable and implantable electronics for health monitoring and generation of piezoelectricity using just a single semiconductor or vdW heterostructures of various nanomaterials. A comparison is also made between the functionality and distinctive properties of 2D flexible electronic devices with a range of applications made from 2D TMDs materials. The current state of the research about 2D TMDs can be applied in a variety of ways in order to aid in the development of new types of nanoscale optoelectronic devices. Last, it summarizes the problems that are currently being faced, along with potential solutions and future prospects.

Paper-based broadband flexible photodetectors with van der Waals materials

Layered metal chalcogenide materials are exceptionally appealing in optoelectronic devices thanks to their extraordinary optical properties. Recently, their application as flexible and wearable photodetectors have received a lot of attention. Herein, broadband and high-performance paper-based PDs were established in a very facile and inexpensive method by rubbing molybdenum disulfide and titanium trisulfide crystals on papers. Transferred layers were characterized by SEM, EDX mapping, and Raman analyses, and their optoelectronic properties were evaluated in a wavelength range of 405–810 nm. Although the highest and lowest photoresponsivities were respectively measured for TiS₃ (1.50 mA/W) and MoS₂ (1.13 μA/W) PDs, the TiS₃–MoS₂ heterostructure not only had a significant photoresponsivity but also showed the highest on/off ratio (1.82) and fast response time (0.96 s) compared with two other PDs. This advantage is due to the band offset formation at the heterojunction, which efficiently separates the photogenerated electron–hole pairs within the heterostructure. Numerical simulation of the introduced PDs also confirmed the superiority of TiS₃–MoS₂ heterostructure over the other two PDs and exhibited a good agreement with the experimental results. Finally, MoS₂ PD demonstrated very high flexibility under applied strain, but TiS₃ based PDs suffered from its fragility and experience a remarkable drain current reduction at strain larger than ± 0.33%. However, at lower strains, all PDs displayed acceptable performances.

Te/SnS2 tunneling heterojunctions as high-performance photodetectors with superior self-powered properties

The tunneling heterojunctions made of two-dimensional (2D) materials have been explored to have many intriguing properties, such as ultrahigh rectification and on/off ratio, superior photoresponsivity, and improved photoresponse speed, showing great potential in achieving multifunctional and high-performance electronic and optoelectronic devices. Here, we report a systematic study of the tunneling heterojunctions consisting of 2D tellurium (Te) and Tin disulfide (SnS₂). The Te/SnS₂ heterojunctions possess type-II band alignment and can transfer to type-III one under reverse bias, showing a reverse rectification ratio of about 5000 and a current on/off ratio over 10⁴. The tunneling heterojunctions as photodetectors exhibit an ultrahigh photoresponsivity of 50.5 A W^-1 in the visible range, along with a dramatically enhanced photoresponse speed. Furthermore, due to the reasonable type-II band alignment and negligible band bending at the interface, Te/SnS₂ heterojunctions at zero bias exhibit excellent self-powered performance with a high responsivity of 2.21 A W^-1 and external quantum efficiency of 678%. The proposed heterostructure in this work provides a useful guideline for the rational design of a high-performance self-powered photodetector.

Vertically oriented SnS2 on MoS2 nanosheets for high-photoresponsivity and fast-response self-powered photoelectrochemical photodetectors

Van der Waals heterostructures have great potential for the emerging self-powered photoelectrochemical photodetectors due to their outstanding photoelectric conversion capability and efficient interfacial carrier transportation. By considering the band alignment, structural design, and growth optimization, the heterostructures of vertically oriented SnS₂ with different densities on MoS₂ nanosheets are designed and fabricated using a two-step epitaxial growth method. Compared with SnS₂, MoS₂, and low density-vertical SnS₂/MoS₂ heterostructure, the high density-vertical SnS₂/MoS₂ heterostructure exhibits largely enhanced self-powered photodetection performances, such as a giant photocurrent density (∼932.8 μA cm^-2), an excellent photoresponsivity (4.66 mA W^-1), and an ultrafast response/recovery time (3.6/6.4 ms) in the ultraviolet-visible range. This impressive enhancement of high density-vertical SnS₂/MoS₂ photodetectors is mainly ascribed to the essentially improved charge transfer and carrier transport of type-II band alignment heterostructures and the efficient light absorption from the unique light-trapping structure. In addition, the photoelectrocatalytic water splitting performance of the high density-vertical SnS₂/MoS₂ heterostructure also benefits from the type-II band alignment and the light-trapping structure. This work provides valuable inspiration for the design of two-dimensional optoelectronic and photoelectrochemical devices with improved performance by the morphology and heterostructure design.

A tellurium short-wave infrared photodetector with fast response and high specific detectivity

Two-dimensional (2D) elementary tellurium (Te) has attracted intensive attention due to its potential applications in short-wave infrared photodetector devices. Here, we report hydrothermally synthesized 2D Te nanoflakes for short-wave infrared photodetectors with high performance. A Te-based photodetector exhibits a peak responsivity of 51.85 A W^-1 at a 1550 nm wavelength, attributed to the efficient absorption of the phonons of 2D Te nanoflakes. Besides, the rising and decay time of the Te photodetector is calculated to be ∼19 μs and ∼21 μs, respectively, due to the rapid diffusion of charge carriers. In addition, Te-photodetectors exhibit a high specific detectivity (D*) of 1.88 × 10¹⁰ Jones and a superior external quantum efficiency (EQE) of 4148%. Our findings have demonstrated the development of high-performance short-wave infrared photodetectors with fast responses based on 2D Te nanoflakes.

Application of Nanostructured TiO2 in UV Photodetectors: A Review

As a wide-bandgap semiconductor material, titanium dioxide (TiO₂ ), which possesses three crystal polymorphs (i.e., rutile, anatase, and brookite), has gained tremendous attention as a cutting-edge material for application in the environment and energy fields. Based on the strong attractiveness from its advantages such as high stability, excellent photoelectric properties, and low-cost fabrication, the construction of high-performance photodetectors (PDs) based on TiO₂ nanostructures is being extensively developed. An elaborate microtopography and device configuration is the most widely used strategy to achieve efficient TiO₂ -based PDs with high photoelectric performances; however, a deep understanding of all the key parameters that influence the behavior of photon-generated carriers, is also highly required to achieve improved photoelectric performances, as well as their ultimate functional applications. Herein, an in-depth illustration of the electrical and optical properties of TiO₂ nanostructures in addition to the advances in the technological issues such as preparation, microdefects, p-type doping, bandgap engineering, heterojunctions, and functional applications are presented. Finally, a future outlook for TiO₂ -based PDs, particularly that of further functional applications is provided. This work will systematically illustrate the fundamentals of TiO₂ and shed light on the preparation of more efficient TiO₂ nanostructures and heterojunctions for future photoelectric applications.

Enhancement of the thermoelectric performance of Cu3SbSe4 particles by controlling morphology using exfoliated selenium nanosheets

Copper antimony selenide (Cu₃SbSe₄), a ternary Cu-based material, is a promising p-type thermoelectric material. In this study, the morphology of Cu₃SbSe₄ particles was controlled using the shape of Se during the synthesis process. To this end, Se particles with a size of 20 μm were exfoliated to form nanosheets through an ultrasonication process without the oxidation of Se. The variation in the morphology of Cu₃SbSe₄ nanoparticles and nanosheets affected their grain size, thus affecting their electrical conductivity and lattice thermal conductivity owing to the phonon and electron scattering at the interface of the grains. By combining the effects of the morphological variation with the electrical and lattice thermal conductivity, the Cu₃SbSe₄ synthesized using Se nanosheets exhibited improved thermoelectric performance. The synthesized Cu₃SbSe₄ nanosheets achieved a maximum thermoelectric figure of merit value of 0.40, which was 1.41 times higher than that of Cu₃SbSe₄ nanoparticles.

In situ construction of a Te/CsPbBr3 heterojunction for self-powered photodetector

In this study, CsPbBr3 particles were prepared by a simple solvent evaporation method in ambient environment; the p-n heterojunction formed by CsPbBr3 particles on the surface of a single long Te wire was used to construct a high-performance Te/CsPbBr3 photodetector. Compared with CsPbBr3 PDs, the Te/CsPbBr3 photodetector showed improved photocurrent, and exhibited characteristics of excellent self-powered performance, broad-spectrum response (UV-visible), and ultra-fast response speed (t rise = 0.09 ms). In addition, under zero bias and upon 540 nm light irradiation, the device had good responsivity (0.35 mA W-1), high photosensitivity (up to 100 on/off ratio), and a detectivity of 1.42 × 1010 Jones. This study provides insight into the possibility of manufacturing high-performance self-powered photodetectors through a simple in situ construction of heterojunctions.

A transparent, self-powered photodetector based on p-CuI/n-TiO2heterojunction film with high on-off ratio

Ultraviolet(UV) photodetectors(PDs) can monitor UV radiation, enabling it to be effective for many applications, such as communication, imaging and sensing. The rapid progress on portable and wearable optoelectronic devices places a great demand on self-powered PDs. However, high-performance self-powered PDs are still limited. Herein we display a transparent and self-powered PD based on a p-CuI/n-TiO₂heterojunction, which exhibits a high on-off ratio (∼10⁴at 310 nm) and a fast response speed (rise time/decay time = 0.11 ms/0.72 ms) without bias. Moreover, the device shows an excellent UV-selective sensitivity as a solar-blind UV PD with a high UV/visible rejection ratio (R_{300 nm}/R_{400 nm}= 5.3 × 10²), which can be ascribed to the wide bandgaps of CuI and TiO₂. This work provides a feasible route for the construction of transparent, self-powered PDs based on p-n heterojunctions.

Sensing of ultraviolet light: a transition from conventional to self-powered photodetector

Clouds in the sky pass almost 80% of ultraviolet (UV) radiation to the earth's surface, which has a significant impact on humankind. Conventional UV photodetectors (PDs) require an external battery, which not only increases the device size but also has a limited life span and maintenance costs can be prohibitively expensive. An alternative and more technically-sound solution would be the use of self-powered UV PDs that can operate independently, eliminating the need for an external source. Although many exciting studies have been done and state-of-the-art research is underway to successfully fabricate self-powered UV PDs, periodic reviews on this topic are deemed essential so that the technology's readiness can be properly evaluated and critical challenges can be addressed in a timely manner. In this article, the key issues and most exciting developments made in recent years on built-in electric field assisted self-powered UV PDs based on p-n homojunctions, p-n heterojunctions, and Schottky junctions followed by energy harvester integrated UV PDs are extensively reviewed. Finally, a summary and comparison of different types of self-powered UV PDs as well as future challenges that need to be addressed are discussed. This review sets a foundation providing essential insights into the present status of self-powered UV PDs with which researchers can engage and deal with the major challenges.

MoS2/WSe2nanohybrids for flexible paper-based photodetectors

Flexible photodetectors functionalized by transition metal dichalcogenides have attracted great attention due to their excellent photo-harvesting efficiency. However, the field of optoelectronics still requires advancement in the production of large-area, broad band and flexible photodetectors. Here we report a flexible, stable, broad band and fast photodetector based on a MoS₂/WSe₂heterostructure on ordinary photocopy paper with pencil-drawn graphite electrodes. Ultrathin MoS₂/WSe₂nanohybrids have been synthesized by an ultrahigh yield liquid-phase exfoliation technique. The thin sheets of WSe₂, and MoS₂contain two to four layers with a highly c-oriented crystalline structure. Subsequently, the photodetector was exploited under ultra-broad spectral range from 400 to 780 nm. The photodetector exhibits excellent figure of merit such as on/off ratio of the order of 10³, photoresponsivity of 124 mA W^-1and external quantum efficiency of 23.1%. Encouragingly, rise/decay time of about 0.1/0.3 s was realized, which is better than in previous reports on paper-based devices.

Fabrication of 1D Te/2D ReS2 Mixed-Dimensional van der Waals p-n Heterojunction for High-Performance Phototransistor

The superior optical and electronic properties of the two-dimensional (2D) rhenium disulfide (ReS₂) makes it suitable for nanoelectronic and optoelectronic applications. However, the internal defects coupled with with the low mobility and light-absorbing capability of ReS₂ impede its utilization in high-performance photodetectors. Fabrication of mixed-dimensional heterojunctions is an alternative method for designing high-performance hybrid photodetectors. This study proposes a mixed-dimensional van der Waals (vdW) heterojunction photodetector, containing high-performance one-dimensional (1D) p-type tellurium (Te) and 2D n-type ReS₂, developed by depositing Te nanowires on ReS₂ nanoflake using the dry transfer method. It can improve the injection and separation efficiency of photoexcited electron-hole pairs due to the type II p-n heterojunction formed at the ReS₂ and Te interface. The proposed heterojunction device is sensitive to visible-light sensitivity (632 nm) with an ultrafast photoresponse (5 ms), high responsivity (180 A/W), and specific detectivity (10⁹), which is superior to the pristine Te and ReS₂ photodetectors. As compared to the ReS₂ device, the responsivity and response speed is better by an order of magnitude. These results demonstrate the fabrication and application potential of Te/ReS₂ mixed-dimensional heterojunction for high-performance optoelectronic devices and sensors.

Room-temperature fabrication of SiC microwire photodetectors on rigid and flexible substrates via femtosecond laser direct writing

Flexible ultraviolet (UV) photodetectors (PDs) have gained increasing demand because of their widespread applications in wearable devices. However, difficulties associated with complicated fabrication technologies significantly limit their scope of application. Herein, via the development of a femtosecond laser direct writing (FsLDW) strategy, silicon carbide (SiC) nanoparticles are found to be assembled in a single microwire within 30 s. The surface of the deposited SiC microwire presents a three-dimensional porous structure, which is conducive to improving the responsivity of the device. The responsivity of a SiC-based microwire PD to UV light at 365 nm is found to be 55.89 A W-1 at a 1 V bias. The as-fabricated SiC microwire PDs on a glass substrate exhibit thermal stability at 350 °C, and the response speed of the PDs becomes notably faster at high temperatures, suggesting their promising applications in harsh conditions. Due to the low-temperature processing characteristics of this process, they can be prepared not only on glass substrates, but also on thermosensitive polymer substrates without an extra transfer process. Moreover, the SiC microwires prepared via FsLDW are directly deposited on the flexible substrate, and the prepared flexible SiC-based PDs can still work stably after being bent 2000 times. This research unveils a feasible way to fabricate a PD with excellent thermal stability and mechanical flexibility.

Electron Acceptors Co-Regulated Self-Powered Photoelectrochemical Strategy and Its Application for Circulating Tumor Nucleic Acid Detection Coupled with Recombinase Polymerase Amplification

Biosensor working in a self-powered mode has been widely concerned because it produces a signal when the bias potential is 0 V. However, the self-powered mode is used only when the materials have self-powered properties. Conversion of non-self-powered to self-powered through molecular regulation can solve this problem effectively. Here, we fabricated a self-powered photoelectrochemical mode based on co-regulation of electron acceptors methylene blue (MB) and p-nitrophenol (p-NP). AuNPs@ZnSe nanosheet-modified gold electrode (AuNPs@ZnSeNSs/GE) gave a small photocurrent at 0 V. In the presence of MB and p-NP, AuNPs@ZnSeNSs/GE gave the strongest photocurrent at 0 V. Accordingly, an electron acceptor co-regulated self-powered photoelectrochemical assay was fabricated. As proof-of-concept demonstrations, this assay was applied for prostate cancer circulating tumor nucleic acid biomarker, KLK2 and PCA3, detection combined with in situ recombinase polymerase amplification strategy. This assay generated a strong photocurrent and was sensitive to the variation of KLK2 and PCA3 concentration. The limits of detection were 30 and 32 aM, respectively. We anticipate this electron acceptor co-regulated self-powered photoelectrochemical mode to pave a new way for the development of self-powered sensing.

Paper-Based Sensors for Gas, Humidity, and Strain Detections: A Review

Paper, as a flexible, low-cost, lightweight, tailorable, environmental-friendly, degradable, and renewable material, is emerging in electronic devices. Especially, many kinds of paper-based (PB) sensors have been reported for wearable applications in recent years. Among them, the PB gas, humidity, and strain sensors are widely studied for monitoring gas, humidity, and strain from the human body and the environment. However, gas, humidity, and strain often coexist and interact, and the paper itself is hydrophilic and flexible, resulting in that it is still challenging to develop high-performance PB sensors specialized for gas, humidity, and strain detections. Therefore, it is necessary to summarize and discuss them systematically. In this review, we focus on summarizing the state-of-art studies of the PB gas, humidity, and strain sensors. Specifically, the fabrications (electrodes and sensing materials) and applications of PB gas, humidity, and strain sensors are summarized and discussed. The current challenges and the potential trends of PB sensors for gas, humidity, and strain detections are also outlined. This review not only can help readers to understand the development status of the PB gas, humidity, and strain sensors but also is helpful for readers to find out and solve the problems in this field through comparative reading.

Graphdiyne-Based Flexible Photodetectors with High Responsivity and Detectivity

Graphdiyne (GDY), a newly emerging 2D carbon allotrope, has been widely explored in various fields owing to its outstanding electronic properties such as the intrinsic bandgap and high carrier mobility. Herein, GDY-based photoelectrochemical-type photodetection is realized by spin-coating ultrathin GDY nanosheets onto flexible poly(ethylene terephthalate) (PET) substrates. The GDY-based photodetectors (PDs) demonstrate excellent photo-responsive behaviors with high photocurrent (P_ph , 5.98 µA cm^{- 2} ), photoresponsivity (R_ph , 1086.96 µA W^{- 1} ), detectivity (7.31 × 10¹⁰ Jones), and excellent long-term stability (more than 1 month). More importantly, the PDs maintain an excellent P_ph after 1000 cycles of bending (4.45 µA cm^{- 2} ) and twisting (3.85 µA cm^{- 2} ), thanks to the great flexibility of the GDY structure that is compatible with the flexible PET substrate. Density functional theory (DFT) calculations are adopted to explore the electronic characteristics of GDY, which provides evidence for the performance enhancement of GDY in alkaline electrolyte. In this way, the GDY-based flexible PDs can enrich the fundamental study of GDY and pave the way for the exploration of GDY heterojunction-based photodetection.

A mixed-dimensional 1D Se-2D InSe van der Waals heterojunction for high responsivity self-powered photodetectors

Mixed-dimension van der Waals (vdW) p-n heterojunction photodiodes have inspired worldwide efforts to combine the excellent properties of 2D materials and traditional semiconductors without consideration of lattice mismatch. However, owing to the scarcity of intrinsic p-type semiconductors and insufficient optical absorption of the few layer 2D materials, a high performance photovoltaic device based on a vdW heterojunction is still lacking. Here, a novel mixed-dimension vdW heterojunction consisting of 1D p-type Se nanotubes and a 2D flexible n-type InSe nanosheet is proposed by a facile method, and the device shows excellent photovoltaic characteristics. Due to the superior properties of the hybrid p-n junction, the mix-dimensional van der Waals heterojunction exhibited high on/off ratios (103) at a relatively weak light intensity of 3 mW cm-2. And a broadband self-powered photodetector ranging from the UV to visible region is achieved. The highest responsivity of the device could reach up to 110 mA W-1 without an external energy supply. This value is comparable to that of the pristine Se device at 5 V and InSe device at 0.1 V, respectively. Furthermore, the response speed is enhanced by one order of magnitude over the single Se or InSe device even at a bias voltage. This work paves a new way for the further development of high performance, low cost, and energy-efficient photodetectors by using mixed-dimensional vdW heterostructures.

Van der Waals Integration of Bismuth Quantum Dots-Decorated Tellurium Nanotubes (Te@Bi) Heterojunctions and Plasma-Enhanced Optoelectronic Applications

Van der Waals (vdW)-integrated heterojunctions have been widely investigated in optoelectronics due to their superior photoelectric conversion capability. In this work, 0D bismuth quantum dots (Bi QDs)-decorated 1D tellurium nanotubes (Te NTs) vdW heterojunctions (Te@Bi vdWHs) are constructed by a facile bottom-up assembly process. Transient absorption spectroscopy suggests that Te@Bi vdWH is a promising candidate for new-generation optoelectronic devices with fast response properties. The subsequent experiments and density functional theory calculations demonstrate the vdW interaction between Te NTs and Bi QDs, as well as the enhanced optoelectronic characteristics owing to the plasma effects at the interface between Te NTs and Bi QDs. Moreover, Te@Bi vdWHs-based photodetectors show significantly improved photoresponse behavior in the ultraviolet region compared to pristine Te NTs or Bi QDs-based photodetectors. The proposed integration of vdWHs is expected to pave the way for constructing new nanoscale heterodevices.

Generation of magnetoelectric photocurrents using toroidal resonances: a new class of infrared plasmonic photodetectors

The detection of photons by plasmonic subwavelength devices underpins spectroscopy, low-power wavelength division multiplexing for short-distance optical communication, imaging, and time-gated distance measurements. In this work, we demonstrate infrared light-sensing using toroidal dipole-resonant plasmonic multipixel meta-atoms. As a key factor, the toroidal dipolar mode is an extremely localized electromagnetic excitation independent of the conventional multipoles. The exquisite behavior of this mode enables significant enhancements in the localized electromagnetic field and absorption cross-section, which boost the field confinement at the metal-dielectric interfaces. The proposed novel approach offers an advanced photodetection of the incident light based on substantial confinement of electromagnetic fields in a tiny spot, giving rise to the generation of hot carriers and a large photocurrent. Using both n- and p-type silicon (Si) substrates, we exploited the free-carrier absorption advantage of p-type Si to devise a high-responsivity device. Our findings show an unprecedented performance for infrared plasmonic photodetectors with low noises, high detectivity and remarkable internal quantum efficiency (IQE). Moreover, the tailored photodetection device provides a significant linear dynamic range of 46 dB and a fast operation speed. Our narrowband infrared light sensing photodevice offers a promising approach for further research studies over the optoelectronic and plasmonic tools and paves a viable route for low-dimensional photonic systems.

Zinc oxide ultraviolet photodetectors: rapid progress from conventional to self-powered photodetectors

Currently, the development of ultraviolet (UV) photodetectors (PDs) has attracted the attention of the research community because of the vast range of applications of photodetectors in modern society. A variety of wide-band gap nanomaterials have been utilized for UV detection to achieve higher photosensitivity. Specifically, zinc oxide (ZnO) nanomaterials have attracted significant attention primarily due to their additional properties such as piezo-phototronic and pyro-phototronic effects, which allow the fabrication of high-performance and low power consumption-based UV PDs. This article primarily focuses on the recent development of ZnO nanostructure-based UV PDs ranging from nanomaterials to architectural device design. A brief overview of the photoresponse characteristics of UV PDs and potential ZnO nanostructures is presented. Moreover, the recent development in self-powered PDs and implementation of the piezo-phototronic effect, plasmonic effect and pyro-phototronic effect for performance enhancement is highlighted. Finally, the research perspectives and future research direction related to ZnO nanostructures for next-generation UV PDs are summarized.