Void-free 3D Bioprinting for In-situ Endothelialization and Microfluidic Perfusion

Recent progress in ultraviolet photodetectors based on low-dimensional materials

Ultraviolet (UV) photodetectors (PDs) are crucial for various advanced applications, yet conventional technologies suffer from limitations like low sensitivity, slow response, and high costs. Low-dimensional materials (LDMs) have emerged as a promising alternative due to their unique optoelectronic properties, including quantum confinement, tunable bandgaps, and high carrier mobility. While existing reviews on UV-PDs often focus narrowly on specific materials or structures, this review offers a comprehensive overview of LDM-based UV-PDs, covering 0D, 1D, and 2D materials and their heterostructures. We highlight recent advances that enhance UV-PD performance across the full UV spectrum, addressing challenges such as limited spectral range and high dark current. The review also explores diverse applications, from medicine to space science, demonstrating the growing impact of LDM-based UV-PDs. By focusing on the latest developments and addressing research gaps, this review provides essential insights into the future of UV photodetection.

Two-Dimensional Transition Metal Dichalcogenides (2D TMDs) Coupled With Zero-Dimensional Nanomaterials (0D NMs) for Advanced Photodetection

The integration of 2D transition metal dichalcogenides (TMDs) with other materials presents a promising approach to overcome inherent limitations and enable the development of novel functionalities. In particular, 0D nanomaterials (0D NMs) offer notable advantages for photodetection, including broadband light absorption, size-dependent optoelectronic properties, high quantum efficiency, and good compatibility. Herein, the integration of 0D NMs with 2D TMDs to develop high-performance photodetectors is reviewed. The review provides a comprehensive overview of different types of 0D NMs, including plasma nanoparticles (NPs), up-conversion NPs, quantum dots (QDs), nanocrystals (NCs), and small molecules. The discussion starts with an analysis of the mechanism of 0D NMs on 2D TMDs in photodetection, exploring various strategies for improving the performance of hybrid 2D TMDs/0D NMs. Recent advancements in photodetectors combining 2D TMDs with 0D NMs are investigated, particularly emphasizing critical factors such as photosensitivity, photogain, specific detectivity, and photoresponse speed. The review concludes with a summary of the current status, highlighting the existing challenges and prospective developments in the advancement of 0D NMs/2D TMDs-based photodetectors.

Graphene/PtSe2/Ultra-Thin SiO2/Si Broadband Photodetector with Large Responsivity and Fast Response Time

Burgeoning two-dimensional (2D) materials provide more opportunities to overcome the shortcomings of silicon-based photodetectors. However, the inevitable carrier loss in the 2D material/Si heterojunction has seriously hindered further improvement in responsivity and detection speed. Here, we propose a graphene/PtSe2/ultra-thin SiO2/Si photodetector (PD) with multiple optimization mechanisms. Due to the fact that photo-generated carriers can travel in the graphene plane toward the Au electrode, the introduction of a top graphene contact with low sheet resistance provides a carrier collection path in the vertical direction and further restricts the carrier recombination behavior at the lateral grain boundary of PtSe2 film. The ultra-thin SiO2 passivation layer reduces the defects at the PtSe2/Si heterojunction interface. As compared to the counterpart device without the graphene top contact, the responsivity, specific detectivity, and response speed of graphene/PtSe2/ultra-thin SiO2/Si PD under 808 nm illumination are improved to 0.572 A/W, 1.50 × 1011 Jones, and 17.3/38.8 µs, respectively. The device can detect broad-spectrum optical signals as measured from 375 nm to 1550 nm under zero bias. The PD line array with 16-pixel units shows good near-infrared imaging ability at room temperature. Our study will provide guiding significance for how to improve the comprehensive properties of PDs based on 2D/Si heterostructure for practical applications.

Enhanced Ultra-narrowband Fast Response Ultraviolet Photodetector based on GaN Homojunction with a Carbon-Doped Semi-insulating Intermediate Layer

A narrowband detection photodetector (PD) serves as a rapid identifier of specific wavebands, holding immense significance in secure communication and spectral recognition. Herein, after carbon is doped into GaN, an acceptor energy level emerges in its band structure, which will compensate with donor states in GaN to reduce carrier concentration and make GaN semi-insulating, and it affected the dark current and electric field distribution of the GaN p-i-n PD. Operating at a bias of 0 V, the C-doped GaN p-i-n PD demonstrates an ultralow dark current density and a high light-to-dark current ratio compared to the undoped intrinsic i-layer GaN p-i-n PD. Moreover, the narrowband response's full width at half-maximum of the PD is only 8.11 nm and displays rapid signal feedback capabilities. Consequently, this prepared C-doped GaN p-i-n PD, which obviates the need for integrating optical filters or employing sophisticated processes, stands to be capable of accurately distinguishing UVA radiation.

High-Performance Broad-Spectrum UV Photodetectors with Uniform Response: Engineering β-Ga2O3:Si/GaN:Si Heterojunctions via Thermal Oxidation for Optoelectronic Logic Gate and Multispectral Imaging

Developing high-performance, broad-spectrum ultraviolet photodetectors (PDs) with uniform response is crucial for optoelectronic applications like spectral analysis, optoelectronic logic gates, and multispectral imaging. This study constructs n-n type β-Ga2O3:Si/GaN:Si heterojunction PDs using thermal oxidation, combining the advantages of β-Ga2O3:Si and GaN:Si for excellent broad-spectrum response (UV-A to UV-C). A proposed channel model for GaN:Si oxidation includes hole formation, vortex structure development, channel formation, and grain growth, providing a basis for understanding β-Ga2O3:Si/GaN:Si heterojunction formation. Uniform Si doping in the β-Ga2O3 layer, achieved through thermal oxidation, reduces resistivity, enhances the collection of photogenerated carriers from the underlying GaN layer, and hence enhances broad-spectrum response performance. The devices exhibit outstanding uniformity and sensitivity across the UV-A to UV-C range, with a peak responsivity of 2.44 × 104 A W-1 and a photocurrent-to-dark current ratio of 1.3 × 105. Applications include optoelectronic logic gates executing "OR gate" and "AND gate" logic operations with 254 and 365 nm UV light, and a single-pixel multispectral imaging system producing high-contrast, clear "CNU" images with 254, 295, and 365 nm UV light. This research advances the understanding of oxide heterojunction formation and offers a method for developing high-performance, uniformly responsive broad-spectrum UV photodetectors for optoelectronic applications.

On-Chip Full-UV-Band Photodetectors Enabled by Hot Hole Extraction

Achieving on-chip, full-UV-band photodetection across UV-A (315-400 nm), UV-B (280-315 nm), and UV-C (100-280 nm) bands remains challenging due to the limitations in traditional materials, which often have narrow detection ranges and require high operating voltages. In this study, we introduce a self-driven, on-chip photodetector based on a heterostructure of hybrid gold nanoislands (Au NIs) embedded in H-glass and cesium bismuth iodide (Cs3Bi2I9). The Au NIs act as catalytic nucleation sites, enhancing crystallinity and facilitating the vertical alignment of the interconnected Cs3Bi2I9 petal-like thin film. A built-in electric field developed at the heterojunction efficiently separates hot holes generated in the Au NIs under UV illumination, transferring them to the valence band of Cs3Bi2I9 and minimizing recombination losses. The device demonstrates an ultrahigh open-circuit voltage of 0.6 V, exceptional responsivity of 0.88 A/W, and a detection threshold of 90 nW/cm2, outperforming the existing thin film-based UV photodetectors under self-driven mode. Long-term stability tests confirmed robust operational reliability under ambient conditions for up to eight months. This architecture, driven by efficient hot hole dynamics, represents a significant advancement for full-UV-band optoelectronics with promising applications in environmental monitoring, flame detection, biomedical diagnostics, and secure communication systems.

Understanding the Role of Active Lattice Oxygen in CO Oxidation Catalyzed by Copper-Doped Mn2O3@MnO2

Although the hopcalite catalyst, primarily composed of manganese oxide and copper oxide, has been extensively studied for carbon monoxide (CO) elimination, there remains significant potential to optimize its structure and activity. Herein, Cu-doped Mn3O2@MnO2 catalysts featuring highly exposed interfacial regions were prepared. The correlation between interfacial exposure and catalytic activity indicates that the interfacial region serves as the active site for CO catalytic oxidation. The characteristic adsorption of CO by Cu species significantly enhances the catalytic activity of the catalyst. And XPS and ICP-OES analyses reveal that Cu ions coexist in both the interlayer and lattice of δ-MnO2. Furthermore, XPS analysis was employed to quantify the average oxidation state (AOS) of Mn and the molar ratios of oxygen species, demonstrating that both surface-adsorbed oxygen and surface lattice oxygen act as reactive oxygen species in the catalytic reaction, playing a crucial role in CO oxidation. Notably, the surface reactive oxygen species influence the adsorption of CO onto Cu species, and the replenishment of these reactive species is identified as the rate-limiting step in the CO catalytic oxidation process.

Crystal structure modulating performances for 213-nm GeO2 solar-blind photodetectors via DC reactive magnetron sputtering method

Owing to the ultra-wide bandgap energy, high thermal conductivity, and ambipolar capability, GeO2 films are receiving great attention for potential applications in power devices and solar-blind photodetectors. However, the precise control of the crystal structure and optical property is a huge challenge due to close free formation energies of multiple phases, inhibiting the GeO2 based practical device applications. Here, we have fabricated quartz and rutile-GeO2 thin films utilizing the magnetron sputtering based synthetic strategy, which exhibit ultra-wide bandgap energies of 5.51 and 5.88 eV. On the foundation of these ultra-wide bandgap semiconductors, obvious photoresponse characteristics have been achieved at 213 nm and the quartz-GeO2 device exhibits better performances including a short fall time of 148.5 ms, a high photo-dark current ratio of 86.65, large photoresponsivity of 4.56 A/W, and high detectivity of 6.78 × 1013 Jones, which can be attributed to the less oxygen defect exists in the quartz-GeO2 film due to the oxygen-rich growth condition and the better lattice matching with sapphire. Our findings suggest that the GeO2 thin film is a candidate material for optoelectronic device applications and will provide a facile and innovative strategy to develop the solar-blind photodetector.

High-Responsivity Self-Powered Photoelectrochemical UV Photodetector Based on Integrated Self-Supporting SiC/ZnS Heterojunction Nanowire Arrays

In the realm of photodetector (PD) technology, photoelectrochemical (PEC) PDs have garnered attention owing to their inherent advantages. Advances in this field depend on functional nanostructured materials, which are pivotal in improving the separation and transport of photogenerated electron-hole pairs to improve device efficiency. Herein, a highly photosensitive PEC UV PD is built using integrated self-supporting SiC/ZnS heterojunction nanowire array photoelectrodes through anodization and chemical deposition. Compared with the original SiC nanoarrays, the optimized SiC/ZnS-25 nanoarrays exhibit high photocurrent density (Dph, 809.2 µA cm-2), rapid rise/decay times (τr/τd, 4/21 ms), high responsivity (Rλ, 1.226 A W-1), remarkable detectivity (D*, 2.517 × 1011 Jones), and large external quantum efficiency (EQE, 40.57%) under 375 nm UV light with a bias voltage of 0.6 V. Furthermore, SiC/ZnS-25 delivers excellent self-powered performance, with Rλ, D*, and EQE reaching 0.91 A W-1, 1.69 × 1011 Jones, and 30.24%, respectively. In addition, the device exhibits excellent long-term operation and aging stability under a bias voltage of 0.6 V and under self-powered conditions. The excellent photodetection behaviors of the SiC/ZnS PEC PD are mainly ascribed to the synergistic effect of the novel well-aligned nanowire geometry, heterojunction with ZnS nanofilms of optimal thickness, and integrated self-supporting configuration of the photoelectrode.

In-Plane Adaptive Heteroepitaxy of 2D Cesium Bismuth Halides with Engineered Bandgaps on c-Sapphire

The heteroepitaxy of 2D materials with engineered bandgaps are crucial to broaden the spectral response for their integrated optoelectronic devices. However, it is a challenge to achieve the high-oriented epitaxy and integration of multicomponent 2D materials with varying lattice constants on the same substrate due to the limitation of lattice matching. Here, in-plane adaptive heteroepitaxy of a series of high-oriented 2D cesium bismuth halide (Cs3Bi2X9, X = I, Br, Cl) single crystals with varying lattice constants from 8.41 to 7.71 Å is achieved on c-plane sapphire with distinct lattice constant of 4.76 Å at a low temperature of 160 °C in an air ambient, benefiting from tolerable interfacial strain by switching compressive stress to tensile stress during a 30° rotation of crystal orientation. First-principles calculation demonstrates that those are all thermodynamically stable phases, deriving from multiple minima of interfacial energy between single crystals and sapphire substrate. The detectivity of Cs3Bi2I9 photodetector reaches up to 3.7 × 1012 Jones, deriving from high single-crystal quality. This work provides a promising experimental strategy and basic theory to boost the heteroepitaxy and integration of 2D single crystals with varying lattice constants on low-cost dielectric substrate, paving the way for their applications in integrated optoelectronics.

Two-Dimensional Phototransistors with van der Waals Superstructure Contacts for High-Performance Photosensing

Semiconducting transition metal dichalcogenides (TMDs) possess exceptional photoelectronic properties, rendering them excellent channel materials for phototransistors and holding great promise for future optoelectronics. However, the attainment of high-performance photodetection has been impeded by challenges pertaining to electrical contact. To surmount this obstacle, we introduce a phototransistor architecture, in which the WS2 channel is connected with an alternating WS2-WSe2 strip superstructure, strategically positioned alongside the source and drain contact regions. Illumination triggers efficient separation of photoexcited electrons and holes due to the type-II staggered band alignment within the superstructure. Consequently, the contact regions exhibit degenerately doped n+ WS2 and p+ WSe2 strips under light illumination, resulting in minimal contact resistivity with the metal electrodes. The resultant WS2 phototransistor exhibits a remarkable responsivity of 2.4 × 106 mA/W and an impressive detectivity of 2.6 × 1012 Jones. Furthermore, our time-resolved measurements reveal the absence of persistent photoconductance. This proposed phototransistor architecture provides a route for high-performance photodetection, effectively surpassing previous limitations associated with electrical contact.

Dual-Response UV Radiation Detector Based on Color Switching and Photoresistance Response for UV Radiation Monitoring

Ultraviolet (UV) irradiation is dangerous and can cause serious skin diseases if skin is excessively exposed to it. Thus, it is highly desirable for human health to monitor the UV radiation intensity. In this report, a flexible and stretchable dual-response UV radiation detector is reported by integrating UV-responsive color-switchable WO3 quantum dots (QDs) with an electrical hydrogel. With the radiation intensity of UV increasing from 0.5 to 10 mW/cm2, the color of the hydrogel switched to dark blue gradually due to the excellent photochromic property of WO3 QDs to UV radiation. Furthermore, a linear relationship can be established between color difference and UV radiation intensity. Hence, the color difference of the hydrogel under solar UV irradiation can be used to estimate the solar UV radiation intensity in daily life. In addition, when the UV radiation intensity is greater than 10 mW/cm2, the photochromic hydrogel converts the colorimetric response into the electrical resistance change. Thus, due to its excellent photochromic and electrical resistance response properties for UV irradiation, the prepared hydrogel provides an idea for developing novel detection instruments.

Self-Powered Photodetectors with High Stability Based on Se Paper/P3HT:Graphene Heterojunction

Photodetectors based on selenium (Se) have attracted significant attention because of their outstanding optoelectronic characteristics, including their rapid reactivity and high photoconductivity. However, the poor responsivity of pure Se limits their further development. In this study, a novel Se-P/P3HT:G photodetector was designed and fabricated by combining an organic semiconductor made of poly-3-hexylthiophene mixed with graphene (P3HT:G) with self-supporting Se paper (Se-P) via spin-coating process. The device possesses a dark current of around 4.23 × 10-12 A and self-powered characteristics at 300-900 nm. At zero bias voltage and 548 nm illumination, the Se-P/P3HT:G photodetector demonstrates a maximum photocurrent of 1.35 × 10-9 A (745% higher than that of Se-P at 0.1 V), a quick response time (16.2/27.6 ms), an on/off ratio of 292, and a maximum detectivity and responsivity of 6.47 × 1011 Jones and 34 mA W-1, respectively. Moreover, Se-P/P3HT:G exhibits superior environmental stability. After one month, the photocurrent value of the Se-P/P3HT:G device held steady at 91.4% of its initial value, and even following pre-treatment at 140 °C, the on/off ratio still remained 17 (at a retention rate of about 5.9%). The excellent thermal stability, environmental reliability, and optoelectronic performance of this heterojunction structure offer a useful pathway for the future advancement of high-performance optoelectronic devices.

Effect of Ga Doping on the Stability and Optoelectronic Properties of ZnSnO Thin Film Transistor

The electrical, stability and optoelectronic properties of GZTO TFTs with different Ga doping concentrations were investigated. Active layers were prepared by co-sputtering GaO and ZTO targets with different sputtering powers. The experimental results show that the surface of GZTO films is smooth, which is favorable for stability. The off-state current is reduced by a factor of 10, the switching ratio is increased to 1.59 × 108, and the threshold voltage shift is reduced in PBS and NBS tests. In addition, the transmittance of all devices is greater than 80% in the visible range, and the optical bandgap of the TFTs is increased from 3.61 eV to 3.84 eV after Ga doping. The current enhancement of the GZTO TFTs is more pronounced under UV irradiation, with higher responsiveness and better-sustained photoconductivity. It is proved that Ga doped into ZTO as a carrier suppressor can better combine with oxygen vacancies and reduce the concentration of oxygen vacancies and oxygen defects compared with Zn and Sn atoms, thus improving stability. GaO, as a wide bandgap material, can improve the optical bandgap of GZTO TFTs so that they can better absorb the light in the UV wavelength band, and they can be used in the field of UV photodetection.

Plasma Metabolic Profiles via p-p Heterojunction-Assisted Laser Desorption/Ionization Mass Spectrometry for Advanced Warning and Diagnosis of Epidural-Related Maternal Fever

Epidural-related maternal fever (ERMF) heightens the risk of intrapartum fever, whereas effective prevention and treatment in clinical practice are currently lacking. Rapid and sensitive screening tools for ERMF are urgently needed to advance relevant research. In response to this challenge, we devise and craft porous Co3O4/CuO hollow polyhedral nanocages with p-p heterojunctions derived from metal-organic frameworks. We employ these p-p heterojunctions in conjunction with high-throughput mass spectrometry to conduct metabolic analysis of substantial plasma samples, with only about 0.03 μL per sample. Leveraging these p-p heterojunctions, metabolic signals from complex plasma can be amplified, with great reproducibility. By harnessing the power of machine learning on these metabolic signals, we are able to achieve advanced warning of ERMF with an area under the curve (AUC) of 0.887-0.975 by the differentially metabolic analysis of plasma samples collected upon admission. Furthermore, we can accurately diagnose ERMF with an AUC of 0.850-1.000 by analyzing plasma samples collected at the time of delivery from individuals who have received epidural analgesia. These breakthroughs offer invaluable insights for clinical decision making during labor and have the potential to significantly reduce the incidence of ERMF.

Recent Advances in the Growth and Compositional Modelling of III-V Nanowire Heterostructures

Nanowire heterostructures offer almost unlimited possibilities for the bandgap engineering and monolithic integration of III-V photonics with Si electronics. The growth and compositional modelling of III-V nanowire heterostructures provides new insight into the formation mechanisms and assists in the suppression of interfacial broadening and optimization of optical properties. Different models have been proposed in the past decade to calculate the interfacial profiles in axial nanowire heterostructures mainly grown by molecular beam epitaxy and metal-organic vapour phase epitaxy. Based on various assumptions, existing models have different sets of parameters and can yield varying results and conclusions. By focusing on deterministic models based on classical nucleation theory and kinetic growth theory of III-V ternary monolayers in nanowires, we summarize recent advancements in the modelling of axial heterostructures in III-V nanowires, describe and classify the existing models, and determine their applicability to predictive modelling and to the fitting of the available experimental data. In particular, we consider the coordinate-dependent generalizations of the equilibrium, nucleation-limited, kinetic, and regular growth models to make interfacial profiles across axial heterostructures in different III-V nanowires. We examine the factors influencing the interfacial abruptness, discuss the governing parameters, limitations, and modelling of particular material systems, and highlight the areas that require further research.

Localized Surface Plasmon Resonance-Enhanced Photocatalytic Antibacterial of In Situ Sprayed 0D/2D Heterojunction Composite Hydrogel for Treating Diabetic Wound

Chronic diabetic wounds pose significant challenges due to uncontrolled bacterial infections, prolonged inflammation, and impaired angiogenesis. The rapid advancement of photo-responsive antibacterial therapy shows promise in addressing these complex issues, particularly utilizing 2D heterojunction materials, which offer unique properties. Herein, an in situ sprayed Bi/BiOCl 0D/2D heterojunction composite fibrin gel with the characteristics of rapid formation and effective near-infrared activation is designed for the treatment of non-healing diabetes-infected wounds. The sprayed composite gel can provide protective shielding for skin tissues and promote endothelial cell proliferation, vascularization, and angiogenesis. The Bi/BiOCl 0D/2D heterojunction, with its localized surface plasmon resonance (LSPR), can overcome the wide bandgap limitation of BiOCl, enhancing the generation of local heat and reactive oxygen species under near-infrared irradiation. This facilitates bacterial elimination and reduced inflammation, supporting the accelerated healing of diabetes-infected wounds. This study underscores the potential of LSPR-enhanced heterojunctions as advanced wound therapies for chronic diabetic wounds.

Highly Emissive Lanthanide-Based 0D Metal Halide Nanocrystals for Efficient Ultraviolet Photodetector

Recently, lanthanide-based 0D metal halides have attracted considerable attention for their applications in X-ray imaging, light-emitting diodes (LEDs), sensors, and photodetectors. Herein, lead-free 0D gadolinium-alloyed cesium cerium chloride (Gd3+-alloyed Cs3CeCl6) nanocrystals (NCs) are introduced as promising materials for optoelectronic application owing to their unique optical properties. The incorporation of Gd3+ in Cs3CeCl6 (CCC) NCs is proposed to increase the photoluminescence quantum yield (PLQY) from 57% to 96%, along with significantly enhanced phase and chemical stability. The structural analysis is performed by density functional theory (DFT) to confirm the effect of Gd3+ in Cs3Ce1- xGdxCl6 (CCGC) alloy system. Moreover, the CCGC NCs are applied as the active layer in UVPDs with different Gd3+ concentration. The excellent device performance is shown at 20% of Gd3+ in CCGC NCs with high detectivity (7.938 × 1011 Jones) and responsivity (0.195 A W-1) at -0.1 V at 310 nm. This study paves the way for the development of lanthanide-based metal halide NCs for next-generation UVPDs and other optoelectronic applications.

Filter-Free UV Photodetectors Based on Unipolar Barrier Van der Waals α-In2Se3/h-BN Heterostructures

Visible-blind ultraviolet (UV) light detection has a wide application range in scenes like space environment monitoring and medical imaging. To realize miniaturized UV detectors with high performance and high integration ability, new device structures without bulky light filters need to be developed based on advanced mechanisms. Here the unipolar barrier van der Waals heterostructure (UB-vdWH) photodetector is reported that realizes filter-free visible-blind UV detection with good stability, robustness, selectivity, and high detection performance. The UB-vdWH shows a responsivity of 2452 A W-1, a photo on-off ratio of 2.94 × 105 and a detectivity of 1.26 × 1015 Jones as a UV detector, owing to the intentionally designed barrier height that suppresses dark current and photoresponse to visible light during the transport process. The good performance remains intact during 104 test cycles or even under high temperatures, which proves the stability, and robustness of the UB-vdWH, thus shows the huge potential for a wider application range.

All-Optic Logical Operations Based on the Visible-Near Infrared Bipolar Optical Response

The burgeoning need for extensive data processing has sparked enthusiasm for the development of a novel optical logic gate platform. In this study, junction field-effect phototransistors based on molybdenum disulfide/Germanium (MoS2/Ge) heterojunctions are constructed as optical logic units. This device demonstrates a positive photoresponse that is attributed to the photoconductivity effect occurring upon irradiation with visible (Vis) light. Under the illumination of near-infrared (NIR) optics with wavelengths within the communication band, the device shows a negative photoresponse, which is associated with the interlayer Coulomb interactions. The current state of the device can be effectively modulated as different logical states by precisely tuning the wavelength and power density of the optical. Within a 3 × 3 MoS2/Ge phototransistor array, five essentially all-optical logic gates ("AND," "OR," "NAND," "NOT," and "NOR") can be achieved in every signal unit. Furthermore, three complex all-optical logical operations are demonstrated by integrating two MoS2/Ge phototransistors in series. Compared to electronic designs, these all-optical logic devices offer a significant reduction in transistor number, with savings of 50-94% when implementing the above-mentioned functions. These results present opportunities for the development of photonic chips with low power consumption, high fidelity, and large volumes.

3D printed UV-sensing optical fiber probes: manufacturing, properties, and performance

UV sensing 3D printed optical fiber hydrogels provide a flexible and precise method of remotely of detecting exposure to UV radiations. The optical fibers were created using digital light processing 3D printing technique with hydrogel composites, including micro-sized photochromic dyes (pink, blue and their combination). When exposed to ultraviolet (UV) radiation, these dyes exhibited specific absorption characteristics, resulting in significant decreases in both reflection and transmittance mode spectra at 560 nm, 620 nm, and 590 nm. Optical fibers of lengths 1, 2, and 3 cm were manufactured in two orientations: vertical and horizontal. Scanning electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction were utilized to characterize the printed fiber probes. The optical performance of the fibers was tested using customized measurement setups. The reflection and transmission of the printed fibers reduced as the length increased due to optical losses. Reflection and transmisson loss of 20-40% can be observed when the length is increased from 1 to 3 cm. The maximum loss in reflection is observed for pink fiber in the presence of UV irradiation. Also, the type of powder used impacted the response and retraction time, whereas the mixed fiber showed the highest response time of 12-20 s under various conditions. The pink dye added fiber probes shows quick response to UV radiation. An increase in the response time is observed with increasing fiber length. The impact of printing orientation on the transmission and reflectance mode operations of optical fibers was assessed. In addition, the stability of the fiber probes are assesed using a green laser having wavelength 532 nm. This work comprehensively examines the optical properties, manufacturing procedures, and sensing capacities of UV-sensitive photochromic optical fiber sensors.

Wafer-Scale Fabrication of Wearable All-Carbon Nanotube Photodetector Arrays

With electronic devices evolving toward portable and high-performance wearables, the constraints of complex and wet processing technologies become apparent. This study presents a scalable photolithography/chemical-free method for crafting wearable all-carbon nanotube (CNT) photodetector device arrays. Laser-assisted patterning and dry deposition techniques directly assemble gas-phase CNTs into flexible devices without any lithography or lift-off processes. The resulting wafer-scale all-CNT photodetector arrays showcase excellent uniformity, wearability, environmental stability, and notable broadband photoresponse, boasting a high responsivity of 44 AW-1 and a simultaneous detectivity of 1.9 × 109 Jones. This research provides an efficient, versatile, and scalable strategy for manufacturing wearable all-CNT device arrays, allowing widespread adoption in wearable optoelectronics and multifunctional sensors.

Epitaxial Growth of the Large-Scale, Highly-Ordered 3D GaN-Truncated Pyramid Array Toward an Ultrahigh Rejection Ratio and Responsivity Visible-Blind Ultraviolet Photodetection

The micro- and nanostructures of III-nitride semiconductors captivate strong interest owing to their distinctive properties and myriad potential applications. Nevertheless, challenges endure in managing the damage inflicted on crystals through top-down processes or achieving extensive control over the large-area growth of these microstructures via bottom-up methods, thereby impacting their optical and electronic properties. Here, we present novel epitaxially grown 3D GaN truncated pyramid arrays (TPAs) on patterned Si substrates, devoid of any catalyst. These GaN TPAs feature highly ordered, large-scale structures, attributed to the utilization of 3D Si substrates and thin AlN interlayers to alleviate epitaxial strains and limit dislocation formation. Comprehensive characterization via scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and cathodoluminescence attests to the superior structural and optical attributes of these crystals. Furthermore, photoluminescence and ultraviolet (UV)-visible diffuse reflectance spectroscopy reveal sharp band-edge emission and significant light trapping in the UV bands. Employing these GaN TPAs, we constructed metal-semiconductor-metal visible-blind UV photodetectors (PDs) incorporating Ti3C2 MXene as Schottky electrodes. These PDs display exceptional responsivity, achieving 5.32 × 103 mA/W at 255 nm and an ultrahigh UV/visible rejection ratio (R255nm/R450nm) approaching 106, which are 1-2 orders of magnitude higher than most recently reported works. This exploration showcases novel GaN-based microstructures characterized by uniformity, ordered geometry, and exemplary crystalline integrity, paving the way for developing optoelectronic applications.

Self-Powered Visible-Blind Ultraviolet Photodetector Based on Organic-Inorganic Hybrid Copper Halide [N(C2H5)4]2[Cu2Br4]

Organic-inorganic hybrid ternary copper halides offer a broader spectrum of structural possibilities for finely tuning their optoelectronic properties. Herein, we demonstrate for the first time the potential of [N(C2H5)4]2[Cu2Br4], a zero-dimensional hybrid copper halide [(TEA)2Cu2Br4], for ultraviolet (UV) photodetection. A self-powered, visible-blind UV photodetector based on a (TEA)2Cu2Br4/GaN heterojunction architecture is developed, exhibiting a high responsivity, a high detectivity, and fast response speeds. The device demonstrates exceptional stability against environmental oxygen/moisture, heat, and UV light illumination, surpassing the stability of reported copper-based UV photodetectors. Our work highlights the significant potential of (TEA)2Cu2Br4 as a lead-free, stable, and efficient material for next-generation UV photodetection technology.

Recent progress of group III-V materials-based nanostructures for photodetection

Due to the suitable bandgap structure, efficient conversion rates of photon to electron, adjustable optical bandgap, high electron mobility/aspect ratio, low defects, and outstanding optical and electrical properties for device design, III-V semiconductors have shown excellent properties for optoelectronic applications, including photodiodes, photodetectors, solar cells, photocatalysis, etc. In particular, III-V nanostructures have attracted considerable interest as a promising photodetector platform, where high-performance photodetectors can be achieved based on the geometry-related light absorption and carrier transport properties of III-V materials. However, the detection ranges from Ultraviolet to Terahertz including broadband photodetectors of III-V semiconductors still have not been more broadly development despite significant efforts to obtain the high performance of III-V semiconductors. Therefore, the recent development of III-V photodetectors in a broad detection range from Ultraviolet to Terahertz, and future requirements are highly desired. In this review, the recent development of photodetectors based on III-V semiconductor with different detection range is discussed. First, the bandgap of III-V materials and synthesis methods of III-V nanostructures are explored, subsequently, the detection mechanism and key figures-of-merit for the photodetectors are introduced, and then the device performance and emerging applications of photodetectors are provided. Lastly, the challenges and future research directions of III-V materials for photodetectors are presented.

Integrating ultraviolet sensing and memory functions in gallium nitride-based optoelectronic devices

Optoelectronic devices present a promising avenue for emulating the human visual system. However, existing devices struggle to maintain optical image information after removing external stimuli, preventing the integration of image perception and memory. The development of optoelectronic memory devices offers a feasible solution to bridge this gap. Simultaneously, the artificial vision for perceiving and storing ultraviolet (UV) images is particularly important because UV light carries information imperceptible to the naked eye. This study introduces a multi-level UV optoelectronic memory based on gallium nitride (GaN), seamlessly integrating UV sensing and memory functions within a single device. The embedded SiO2 side-gates around source and drain regions effectively extend the lifetime of photo-generated carriers, enabling dual-mode storage of UV signals in terms of threshold voltage and ON-state current. The optoelectronic memory demonstrates excellent robustness with the retention time exceeding 4 × 104 s and programming/erasing cycles surpassing 1 × 105. Adjusting the gate voltage achieves five distinct storage states, each characterized by excellent retention, and efficiently modulates erasure times for rapid erasure. Furthermore, the integration of the GaN optoelectronic memory array successfully captures and stably stores specific UV images for over 7 days. The study marks a significant stride in optoelectronic memories, showcasing their potential in applications requiring prolonged retention.

Wide Bandgap Semiconductors for Ultraviolet Photodetectors: Approaches, Applications, and Prospects

Ultraviolet (UV) light, invisible to the human eye, possesses both benefits and risks. To harness its potential, UV photodetectors (PDs) have been engineered. These devices can convert UV photons into detectable signals, such as electrical impulses or visible light, enabling their application in diverse fields like environmental monitoring, healthcare, and aerospace. Wide bandgap semiconductors, with their high-efficiency UV light absorption and stable opto-electronic properties, stand out as ideal materials for UV PDs. This review comprehensively summarizes recent advancements in both traditional and emerging wide bandgap-based UV PDs, highlighting their roles in UV imaging, communication, and alarming. Moreover, it examines methods employed to enhance UV PD performance, delving into the advantages, challenges, and future research prospects in this area. By doing so, this review aims to spark innovation and guide the future development and application of UV PDs.

Achieving water-floatable photocatalyst on recycled bamboo chopsticks

Disposable bamboo chopsticks (DBCs) are difficult to recycle, which inevitably cause secondary pollution. Based on energy and environmental issues, we propose a facile strategy to fabricate floatable photocatalyst (fPC) coated onto DBCs, which can be flexibly used in water purification. The photocatalyst of titania and titanium carbide on bamboo (TiO2/TiC@b) was successfully constructed from TiC-Ti powders and DBCs using a coating technique followed heat treatment in carbon powder, and the fPC exhibited excellent photocatalytic activity under visible light irradation. The analysis results indicate that rutile TiO2 forms on TiC during heat treatment, achieving a low-density material with an average value of approximately 0.5233 g/cm3. The coatings of TiO2/TiC on the bamboo are firm and uniform, with a particle size of about 20-50 nm. XPS results show that a large amount of oxygen vacancies is generated, due to the reaction atmosphere of more carbon and less oxygen, further favoring to narrowing the band gap of TiO2. Furthermore, TiO2 formed on residual TiC would induce the formation of a heterojunction, which effectively inhibits the photogenerated electron-hole recombination via the charge transfer effect. Notably, the degradation of dye Rhodamine B (Rh.B) is 62.4% within 3 h, while a previous adsorption of 36.0% for 1 h. The excellent photocatalytic performance of TiO2/TiC@b can be attributed to the enhanced reaction at the water/air interface due to the reduced light loss in water, improved visible-light response, increased accessible area and charge transfer effect. Our findings show that the proposed strategy achieves a simple, low-cost, and mass-producible method to fabricate fPC onto the used DBCs, which is expected to applied in multiple fields, especially in waste recycling and water treatment.

A Broadband Photodetector Based on Non-Layered MnS/WSe2 Type-I Heterojunctions with Ultrahigh Photoresponsivity and Fast Photoresponse

The separation of photogenerated electron-hole pairs is crucial for the construction of high-performance and wide-band responsive photodetectors. The type-I heterojunction as a photodetector is seldomly studied due to its limited separation of the carriers and narrow optical response. In this work, we demonstrated that the high performance of type-I heterojunction as a broadband photodetector can be obtained by rational design of the band alignment and proper modulation from external electric field. The heterojunction device is fabricated by vertical stacking of non-layered MnS and WSe2 flakes. Its type-I band structure is confirmed by the first-principles calculations. The MnS/WSe2 heterojunction presents a wide optical detecting range spanning from 365 nm to 1550 nm. It exhibits the characteristics of bidirectional transportation, a current on/off ratio over 103, and an excellent photoresponsivity of 108 A W-1 in the visible range. Furthermore, the response time of the device is 19 ms (rise time) and 10 ms (fall time), which is much faster than that of its constituents MnS and WSe2. The facilitation of carrier accumulation caused by the interfacial band bending is thought to be critical to the photoresponse performance of the heterojunction. In addition, the device can operate in self-powered mode, indicating a photovoltaic effect.

Enabling Broadband Solar-Blind UV Photodetection by a Rare-Earth Doped Oxyfluoride Transparent Glass-Ceramic

Oxyfluoride transparent glass-ceramics (GC) are widely used as the matrix for rare-earth (RE) ions due to their unique properties such as low phonon energy, high transmittance, and high solubility for RE ions. Tb3+ doped oxyfluoride glasses exhibit a large absorption cross section for ultraviolet (UV) excitation, high stability, high photoluminescence quantum efficiency, and sensitive spectral conversion characteristics, making them promising candidate materials for use as the spectral converter in UV photodetectors. Herein, a Tb3+ doped oxyfluoride GC is developed by using the melt-quenching method, and the microstructure and optical properties of the GC sample are carefully investigated. By combining with a Si-based photo-resistor,a solar-blind UV detector is fabricated, which exhibits a significant photoelectric response with a broad detection range from 188 to 400 nm. The results indicate that the designed UV photodetector is of great significance for the development of solar-blind UV detectors.

Air-Stable Self-Driven UV Photodetectors on Controllable Lead-Free CsCu2I3 Microwire Arrays

The rapid evolution of the Internet of Things has engendered increased requirements for low-cost, self-powered UV photodetectors. Herein, high-performance self-driven UV photodetectors are fabricated by designing asymmetric metal-semiconductor-metal structures on the high-quality large-area CsCu2I3 microwire arrays. The asymmetrical depletion region doubles the photocurrent and response speed compared to the symmetric structure device, leading to a high responsivity of 233 mA/W to 355 nm radiation. Notably, at 0 V bias, the asymmetric device produces an open-circuit voltage of 356 mV and drives to a short-circuit current of 372 pA; meanwhile, the switch ratio (Iph/Idark) reaches up to 103, indicating its excellent potential for detecting weak light. Furthermore, the device maintains stable responses throughout 10000 UV-light switch cycles, with negligible degradation even after 90-day storage in air. Our work establishes that CsCu2I3 is a good candidate for self-powered UV detection and thoroughly demonstrates its potential as a passive device.

Wide Response Range Photoelectrochemical UV Detector Based on Anodized TiO2-Nanotubes@Ti@quartz Structure

Conventional sandwich structure photoelectrochemical UV detectors cannot detect UV light below 300 nm due to UV filtering problems. In this work, we propose to place the electron collector inside the active material, thus avoiding the effect of electrodes on light absorption. We obtained a TiO2-nanotubes@Ti@quartz photoanode structure by precise treatment of a commercial Ti mesh by anodic oxidation. The structure can absorb any light in the near-UV band and has superior stability to other metal electrodes. The final encapsulated photoelectrochemical UV detectors exhibit good switching characteristics with a response time below 100 ms. The mechanism of the oxidation conditions on the photovoltaic performance of the device was investigated by the electrochemical impedance method, and we obtained the optimal synthesis conditions. Response tests under continuous spectroscopy confirm that the response range of the device is extended from 300-400 nm to 240-400 nm. This idea of a built-in collector is an effective way to extend the response range of a photoelectrochemical detector.

Dipole Field-Driven Organic-Inorganic Heterojunction for Highly Sensitive Ultraviolet Photodetector

Developing high-performance organic-inorganic ultraviolet (UV) photodetectors (PDs) has attracted considerable attention. However, this development has been hindered due to poor directional charge-transfer ratios in transport layers, excessive costs, and an ambiguous underlying mechanism. To tackle these challenges, we constructed a heterojunction of economic Mg-doped ZnO (MgZnO) nanorods and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) [PEDOT:PSS (P:P)] that utilizes dipole field-driven spontaneous polarization to enhance photogenerated charge kinetics. As a result, the proposed heterojunction has an improved noise equivalent power of 3.16 × 10-11 W Hz-1/2), a normalized detection rate (D*) of 8.96 × 109 jones, and external quantum efficiency comparable to other ZnO-based devices. Notably, the prepared PDs showed a photocurrent of 4.8 × 10-3 μA under a faint UV light having an intensity of 1 × 10-5 W cm-2, exceeding the performance of the most state-of-the-art ZnO-based UV sensors. The introduction of Mg into ZnO is responsible for the high performance, as it causes a lattice mismatch and distortion of the Mg-doped ZnO unit cell. It results in improved dipole movement and the creation of a dipole field, accelerating the directional electron-transfer process. Using a dipole field to manipulate the migration and transport of photogenerated carriers represents a promising approach for achieving outstanding performance in UV PDs.

Self-powered, wide spectral UV response out-of-plane photodetector based on ZnO/porous silicon heterostructure

The photoresponse of the ZnO/porous silicon (p-Si) heterojunction is studied in an out-of-plane contact configuration. p-Si substrate is fabricated by anodic etching followed by the electrochemical deposition of ZnO NR film, forming ZnO/p-Si heterojunction. XRD study is done to understand the effect of the substrate on ZnO film growth in terms of strain and crystal size. UV-vis absorbance spectrum shows a broad absorption for wavelengths from 230 to 380 nm. The PL emission shows two narrow and prominent electron transition peaks at 263 and 383 nm and a peak of ∼550 nm corresponding to defects. The 263 nm wavelength responsivity of the photodetector from UV-vis and PL data suggests the presence of a defective SiOxas an intermediate layer between ZnO and p-Si. The photodetector is measured for its spectral selectivity and responsivity for both 266 and 370 nm. Under self-powered conditions, the device shows a low dark current of a few nA and enhancement of ∼100 nA and ∼1.37μA for both wavelengths. A responsivity of 527 mA W-1and 10.5μA W-1and detectivity of 2.5 × 1010and 2.9 × 107Jones at 1 V bias under 266 and 370 nm UV illumination are observed. The fast rise/decay time of 67/65 ms and 29/18 ms is observed for the self-powered condition of the device under both wavelengths respectively. The photoresponse of the modified ZnO/SiOx/p-Si heterojunction for both wavelengths is analyzed for the electron transfer mechanism using the heterojunction band bending model. The short circuit current and open circuit voltage of the photodetector is estimated to be 293 nA, 56.33 mV, and 13.63μA, 124.8 mV for 266 and 370 nm, respectively. It is concluded that the 266 nm responsivity comes from the defects in SiOxintermediate layer, and the photocurrent generated in the device is due to tunneling across the junction.

Recent Advances in Low-Dimensional Nanomaterials for Photodetectors

New emerging low-dimensional such as 0D, 1D, and 2D nanomaterials have attracted tremendous research interests in various fields of state-of-the-art electronics, optoelectronics, and photonic applications due to their unique structural features and associated electronic, mechanical, and optical properties as well as high-throughput fabrication for large-area and low-cost production and integration. Particularly, photodetectors which transform light to electrical signals are one of the key components in modern optical communication and developed imaging technologies for whole application spectrum in the daily lives, including X-rays and ultraviolet biomedical imaging, visible light camera, and infrared night vision and spectroscopy. Today, diverse photodetector technologies are growing in terms of functionality and performance beyond the conventional silicon semiconductor, and low-dimensional nanomaterials have been demonstrated as promising potential platforms. In this review, the current states of progress on the development of these nanomaterials and their applications in the field of photodetectors are summarized. From the elemental combination for material design and lattice structure to the essential investigations of hybrid device architectures, various devices and recent developments including wearable photodetectors and neuromorphic applications are fully introduced. Finally, the future perspectives and challenges of the low-dimensional nanomaterials based photodetectors are also discussed.

Enhancing Visible-Light Absorption of 2D Carbon Nitride by Constructing 2D/2D van der Waals Heterojunctions of Carbon Nitride/Nitrogen-Superdoped Graphene

Carbon nitride sheets (CNs) down to the two-dimensional (2D) limit have been widely used in photoelectric conversion due to their inherent band gap and extremely short charge-carrier diffusion distance. However, the utilization of visible light remains low due to the rapid recombination of photogenerated electron-hole pairs and enlarged band gap. Here, atomically thin 2D/2D van der Waals heterojunctions (vdWHs) of N-superdoped graphene (NG) and CNs (CNs/NG) are fabricated via a facile electrostatic self-assembly method. Our results revealed that the vdWHs can increase the visible-light absorption of CNs by extending the absorption edge from 455 to up to 490 nm. The recombination of photogenerated electron-hole pairs is inhibited because superdoped N in CNs/NG facilitates the transmission of photogenerated carriers in the melon chain. This study opens a new avenue for narrowing the band gap and promoting photoexcited carrier separation in carbon-nitride-based materials.

The van der Waals interaction and absorption and electron circular dichroism spectra of two-dimensional bilayer stacked structures

van der Waals (vdW) heterojunctions based on two-dimensional (2D) materials, graphene and transition metal dichalcogenides (TMDs), are a research hotspot for future optoelectronic and exciton devices. Bond-free vdW interactions are key to 2D material heterojunction device reliability and stability. However, most of the current research on 2D stacked materials heterostructures mainly focuses on optical properties and electronic structure. Furthermore, vdW interaction in 2D heterostructures is studied and understood on the basis of qualitative description and energy ranges from the literature. There are few studies on the nature of vdW interaction based on practical calculations of the quantitative strength and microscopic mechanism of vdW interaction between 2D stacked materials. Therefore, this paper explores the vdW interaction between 2D material stacked bilayer structures, including bilayer graphene, graphene/MoS2 and graphene/WS2 heterostructures, focusing on quantitative analysis of the energy components of the vdW interaction. We first visually observed the weak interactions in the three stacked bilayer structures through noncovalent interaction (NCI) analysis, and found that the interactions are concentrated in the binding region between the two-layer structures. We mainly decomposed the weak interaction energy in the three 2D material bilayer heterostructures through energy decomposition analysis based on the force field (EDA-FF) method and obtained the energy values and proportions of the three components-electrostatic energy, exchange repulsion energy and dispersion energy of the total binding energy between the 2D stacked bilayer structures. The vdW interaction energy is the sum of the exchange repulsion energy and dispersion energy, and the dispersion energy of the vdW interaction accounts for more than 60% of the binding energy of the weak interaction between the 2D bilayer stacked structures. The vdW strengths in the bilayer structures are on the order of 177.07, 123.85, and 133.93 kJ/mol, approxmately 1-2 orders of magnitude larger than the classically defined vdW energies of 0.1-10 kJ/mol. Furthermore, we calculate the density of states of the three 2D stacked structures, and further obtained HOMO-LOMO information; to further understand the electronic structures of the graphene/MoS2 and graphene/WS2 heterostructures, we calculated their optical absorption spectra and electron circular dichroism (ECD) spectra. According to the calculation results, the two heterostructures have strong absorption peaks in the visible region, and the charge transfer forms at the strong absorption peak can be determined according to the charge transfer diagram. The ECD spectra indicate that the configurations of the graphene/MoS2 and graphene/WS2 heterostructures have large chirality. Our work contributes to a deeper understanding of the nature of the weak interactions and optical properties in 2D stacked materials, which plays a fundamental role in promoting the construction of stable 2D heterostructure configurations and the development of multifunctional 2D devices. The research is conducive to further promoting the basic research and practical development of strong optoelectronic and excitonic 2D heterojunctions devices.

Polarization-sensitive UV photodetector based on ReSe2/GaN mixed-dimensional heterojunction

Polarization-sensitive photodetectors in the ultraviolet (UV) region have been favored for their great meaning in the field of military and civilian. UV photodetectors based on GaN have aroused much attention due to high photocurrent and high sensitivity. However, the dependence on external power sources and the limited sensitivity to polarized UV light significantly impede the practical application of these photodetectors in UV-polarized photodetection. Herein, a polarization-sensitive UV photodetector based on ReSe2/GaN mixed-dimensional van der Waals (vdWs) heterojunction is proposed. Owing to the high-quality junction and type-II band alignment, the responsivity and specific detectivity reach values of 870 mA/W and 6.8 × 1011 Jones, under 325 nm illumination, respectively. Furthermore, thanks to the strong in-plane anisotropy of ReSe2, the device is highly sensitive to polarized UV light with a photocurrent anisotropic ratio up to 6.67. The findings are expected to bring new opportunities for the development of highly sensitive, high-speed and energy-efficient polarization-sensitive photodetectors.

Delaminated MnPS3 with Multiple Layers Coupled with Si Featuring Ultrahigh Detectivity and Environmental Stability for UV Photodetection

Silicon (Si), the dominant semiconductor in microelectronics yet lacking optoelectronic functionalities in UV regions, has been researched extensively to make revolutionary changes. In this study, the inherent drawback of Si on optoelectronic functionalities in UV regions is potentially overcome through heterostructure coupling of delaminated p-type MnPS3, having bulk, multiple-layer, and few-layer features, with n-type Si. By artificially mimicking the architectures of shrubs with unique UV shading phenomena, the revolutionary multiple-layer MnPS3 structures with staggered stacking configurations trigger outstanding UV photosensing performances, displaying an average EQE value of 1.1 × 103%, average photoresponsivity of 3.1 × 102 A/W, average detectivity of 1.9 × 1014 cm Hz1/2W1-, and average on/off ratio of 1.8 × 103 under 365 nm light. To the best of our knowledge, this is the first attempt toward realizing gate-free MnPS3-based UV photodetectors, while all of the photodetection outcomes are better than those of more sophisticated field-effect transistor (FET) designs, which have remarkable impacts on the practicality and functionality of next-generation UV optoelectronics.

Ideal Vacuum-Based Efficient and High-Throughput Computational Screening of Type II Heterojunctions

Heterojunctions featuring a type II band alignment play a crucial role in a wide range of devices, particularly in the realm of solar cells. However, the design of such heterojunctions with a specific type of band alignment poses a substantial challenge due to the immense number of potential combinations of bulk semiconductors and their relative orientations. In this study, we propose an efficient, high-throughput computational screening method tailored for heterojunctions. Our approach, using the ideal vacuum level as a reference energy, eliminates the need for explicit electronic structure calculations for junctions. Through this protocol, we identify 1041 type II heterojunctions out of 2692 structures constructed from 86 selected inorganic compounds with appropriate band gaps sourced from the Inorganic Crystal Structure Database. For potential application in solar cells, we assess these heterojunctions, and remarkably, 58 of them exhibit a power conversion efficiency (PCE) exceeding 15%, with 13 surpassing the 20% threshold. Test calculations with expensive interface models confirm the reliability of PCE predictions based on ideal vacuums. These predictions will be of benefit in assessing the material applicability for solar cell applications. Furthermore, the versatility of our proposed screening method extends beyond solar cells, making it a valuable theoretical design tool that can be applied to a wide range of heterojunction devices.

Over 5 × 103-Fold Enhancement of Responsivity in Ga2O3-Based Solar Blind Photodetector via Acousto-Photoelectric Coupling

The emergence of the wide-band-gap semiconductor Ga2O3 has propelled it to the forefront of solar blind detection activity owing to its key features. Although various architectures and designs of Ga2O3-based solar blind photodetectors have been proposed, their performance still falls short of commercial standards. In this study, we demonstrate a method to enhance the performance of a simple metal-semiconductor-metal-structured Ga2O3-based solar blind photodetector by exciting acoustic surface waves. Specifically, we demonstrate that under a bias voltage of 100 mV and a radio frequency signal of 20 dBm, the responsivity and detectivity can increase from 2.78 to 1.65 × 104 A/W and from 8.35 × 1014 to 2.66 × 1016 jones, respectively, rivaling a commercial photomultiplier tube. The over 5 × 103-fold enhancement in responsivity could be attributed to the acousto-photoelectric coupling mechanism. Furthermore, since surface acoustic waves can also serve as signal receivers, such photodetectors offer the prospect of dual-mode detection. Our findings reveal a promising pathway for achieving high-performance Ga2O3-based electronics and optoelectronics.

Ferroelectric polarization reversals in C2N/α-In2Se3 van der Waals heterostructures: a conversion from the traditional type-II to S-scheme

Introduction: Ferroelectric substances, characterized by inherent spontaneous polarization, can boost photocatalytic efficiency by facilitating the separation of photogenerated carriers. However, conventional photocatalysts with perovskite-class ferroelectricity are generally constrained by their 3D arrangement, leading to less accessible active sites for catalysis and a smaller specific surface area compared to a 2D layout. Methods: In my research, I developed a 2D ferroelectric heterostructure consisting of C2N/α-In2Se3. I performed first-principle calculations on the 2D C2N/α-In2Se3 heterostructure, specifically varying the out-of-plane ferroelectric polarization directions. I primarily focused on C2N/α-In2Se3 (I) and C2N/α-In2Se3 (II) heterostructures. Results: My findings revealed that reversing the ferroelectric polarization of the 2D α-In2Se3 layer in the heterostructures led to a transition from the conventional type-II [C2N/α-In2Se3 (I)] to an S-scheme [C2N/α-In2Se3 (II)]. The S-scheme heterostructure [C2N/α-In2Se3 (II)] demonstrated a high optical absorption rate of 17% in visible light, marking it as a promising photocatalytic material. Discussion: This research underscores the significance of ferroelectric polarization in facilitating charge transfer within heterogeneous structures. It provides a theoretical perspective for developing enhanced S-scheme photocatalysts, highlighting the potential of 2D ferroelectric heterostructures in photocatalytic applications.

Metal-semiconductor-metal solar-blind ultraviolet photodetector based on Al0.55Ga0.45N/Al0.4Ga0.6N/Al0.65Ga0.35N heterostructures

We have designed a metal-semiconductor-metal (MSM) solar-blind ultraviolet (UV) photodetector (PD) by utilizing Al0.55Ga0.45N/Al0.4Ga0.6N/Al0.65Ga0.35N heterostructures. The interdigital Ni/Au metal stack is deposited on the Al0.55Ga0.45N layer to form Schottky contacts. The AlGaN hetero-epilayers with varying Al content contribute to the formation of a two-dimensional electron gas (2DEG) conduction channel and the enhancement of the built-in electric field in the Al0.4Ga0.6N absorption layer. This strong electric field facilitates the efficient separation of photogenerated electron-hole pairs. Consequently, the fabricated PD exhibits an ultra-low dark current of 1.6 × 10-11 A and a broad spectral response ranging from 220 to 280 nm, with a peak responsivity of 14.08 A/W at -20 V. Besides, the PD demonstrates an ultrahigh detectivity of 2.28 × 1013 Jones at -5 V. Furthermore, to investigate the underlying physical mechanism of the designed solar-blind UV PD, we have conducted comprehensive two-dimensional device simulations.

Boosting Charge Utilization in Self-Powered Photodetector for Real-Time High-Throughput Ultraviolet Communication

Ultraviolet (UV) communication is a cutting-edge technology in communication battlefields, and self-powered photodetectors as their optical receivers hold great potential. However, suboptimal charge utilization has largely limited the further performance enhancement of self-powered photodetectors for high-throughput communication application. Herein, a self-powered Ti3 C2 Tx -hybrid poly(3,4 ethylenedioxythiophene):poly-styrene sulfonate (PEDOT:PSS)/ZnO (TPZ) photodetector is designed, which aims to boost charge utilization for desirable applications. The device takes advantage of photothermal effect to intensify pyro-photoelectric effect as well as the increased conductivity of the PEDOT:PSS, which significantly facilitated charge separation, accelerated charge transport, and suppressed interface charge recombination. Consequently, the self-powered TPZ photodetector exhibits superior comprehensive performance with high responsivity of 12.3 mA W-1 and fast response time of 62.2 µs, together with outstanding reversible and stable cyclic operation. Furthermore, the TPZ photodetector has been successfully applied in an integrated UV communication system as the self-powered optical receiver capable of real-time high-throughput information transmission with ASCII code under 9600 baud rate. This work provides the design insight of highly performing self-powered photodetectors to achieve high-efficiency optical communication in the future.

Demonstration of a roll-to-roll-configurable, all-solution-based progressive assembly of flexible transducer devices consisting of functional nanowires on micropatterned electrodes

We demonstrate continuous fabrication of flexible transducer devices consisting of interdigitated (IDT) Ag microelectrodes interconnected by ZnO nanowires (ZNWs), created via serially connected solution-processable micro- and nanofabrication processes. On an Ag layer obtainable from the mild thermal reduction of an ionic Ag ink coating, the roll-to-roll-driven photolithography process [termed photo roll lithography (PRL)] followed by wet-etching can be applied to continuously define the IDT microelectrode structure. Conformal ZNWs can then be grown selectively on the Ag electrodes to interconnect them via an Ag-mediated hydrothermal ZNW growth that does not require high-temperature seed sintering. Given that all of these constitutive processes are vacuum-free and solution-processable at a low temperature, and are compatible with continuous processing onto flexible substrates, they can be eventually configured into the roll-to-roll-processable progressive assembly. Through parametric optimizations of processes consisting of the roll-to-roll-configurable, solution-based progressive assembly of nanostructures (ROLSPAN), a flexible transducer consisting of ZNW-interconnected, PRL-ed IDT Ag electrodes can be developed. This flexible architecture faithfully performs UV sensing as well as optoelectronic transduction. The ROLSPAN concept along with its specific applicability to flexible devices may inspire many diverse functional systems requiring high-throughput low-temperature fabrication over large-area flexible substrates.

Enhancing UV-C Photoelectron Lifetimes for Avalanche-like Photocurrents in Carbon-Doped Bi3O4Cl Nanosheets

Interlayer electric fields in two-dimensional (2D) materials create photoelectron protecting barriers useful to mitigate electron-hole recombination. However, tuning the interlayer electric field remains challenging. Here, carbon-doped Bi₃O₄Cl (C:Bi₃O₄Cl) nanosheets are synthesized using a gas phase protocol, and n-type carriers are acquired as confirmed by the transconductance polarity of nanosheet field effect transistors. Thin C:Bi₃O₄Cl nanosheets show excellent 266 nm photodetector figures of merit, and an avalanche-like photocurrent is demonstrated. Decaying behaviors of photoelectrons pumped by a 266 nm laser pulse (266 nm photoelectrons) are observed using transient absorption spectroscopy, and a significant 266 nm photoelectron lifetime quality in C:Bi₃O₄Cl is presented. Built C:Bi₃O₄Cl models suggest that the interlayer electric field can be boosted by two different carbon substitutions at the inner and outer bismuth sites. This work reports a facile approach to increase the interlayer electric field in Bi₃O₄Cl for future UV-C photodetector applications.

High-Performance Ultraviolet Photodetector Based on Single-Crystal Integrated Self-Supporting 4H-SiC Nanohole Arrays

Currently, the photodetectors (PDs) assembled by vertically aligned nanostructured arrays have attracted intensive interest owing to their unique virtues of low light reflectivity and rapid charge transport. However, in terms of the inherent limitations caused by numerous interfaces often existed within the assembled arrays, the photogenerated carriers cannot be effectively separated, thus weakening the performance of target PDs. Aiming at resolving this critical point, a high-performance ultraviolet (UV) PD with a single-crystal integrated self-supporting 4H-SiC nanohole arrays is constructed, which are prepared via the anode oxidation approach. As a result, the PD delivers an excellent performance with a high switching ratio (∼250), remarkable detectivity (6 × 10¹⁰ Jones), fast response (0.5 s/0.88 s), and excellent stability under 375 nm light illumination with a bias voltage of 5 V. Moreover, it has a high responsivity (824 mA/W), superior to those of most reported ones based on 4H-SiC. The overall high performance of the PDs could be mainly attributed to the synergistic effect of the SiC nanohole arrays' geometry, a whole single-crystal integrated self-supporting film without interfaces, established reliable Schottky contact, and incorporated N dopants.

Wearable Electronics Based on Stretchable Organic Semiconductors

Wearable electronics are attracting increasing interest due to the emerging Internet of Things (IoT). Compared to their inorganic counterparts, stretchable organic semiconductors (SOSs) are promising candidates for wearable electronics due to their excellent properties, including light weight, stretchability, dissolubility, compatibility with flexible substrates, easy tuning of electrical properties, low cost, and low temperature solution processability for large-area printing. Considerable efforts have been dedicated to the fabrication of SOS-based wearable electronics and their potential applications in various areas, including chemical sensors, organic light emitting diodes (OLEDs), organic photodiodes (OPDs), and organic photovoltaics (OPVs), have been demonstrated. In this review, some recent advances of SOS-based wearable electronics based on the classification by device functionality and potential applications are presented. In addition, a conclusion and potential challenges for further development of SOS-based wearable electronics are also discussed.

Water-soluble graphene quantum dot-based polymer nanoparticles with internal donor/acceptor heterojunctions for efficient and selective detection of cancer cells

We present a new, insightful donor-acceptor (D-A) energy transfer-based strategy for the preparation and development of water-soluble multifunctional pH-responsive heterojunction nanoparticles. Hydrophilic tertiary amine-grafted polythiophene (WPT) as a donor and blue fluorescent graphene quantum dots (GQD) as an acceptor spontaneously form co-assembled nanoparticles that function as a highly pH-sensitive and efficient biosensor appropriate for the detection of cancer cells. These WPT/GQD nanoparticles exhibit a number of unique physical characteristics-such as broad-range, tunable GQD-loading contents and particle sizes, extremely low cytotoxicity in normal and cancer cells, and highly sensitive pH-responsiveness and rapid acid-triggered fluorescent behavior under aqueous acidic conditions. We show these features are conferred by self-aggregation of the GQD within the nanoparticles and subsequent aggregation-induced fluorescence of GQD after disassembly of the nanoparticles and dissociation of the D-A interactions under acidic conditions. Importantly, in vitro fluorescence imaging experiments clearly demonstrated the WPT/GQD nanoparticles were gradually taken up into normal and cancer cells in vitro. Selective formation of GQD aggregates subsequently occurred in the acidic microenvironment of the cancer cells and the interior of the cancer cells exhibited strong blue fluorescence; these phenomena did not occur in normal cells. In contrast, pristine WPT and GQD did not exhibit cellular microenvironment-triggered fluorescence transitions in cancer or normal cell lines. Therefore, this newly discovered water-soluble heterojunction system may represent a strongly fluorescent highly pH-sensitive bioprobe for rapid detection of cancer cells.