Monolithic Perovskite-Silicon Dual-Band Photodetector for Efficient Spectral Light Discrimination.

Selective spectral discrimination of visible and near-infrared light, which accurately distinguishes different light wavelengths, holds considerable promise in various fields, such as automobiles, defense, and environmental monitoring. However, conventional imaging technologies suffer from various issues, including insufficient spatial optimization, low definition, and optical loss. Herein, a groundbreaking advancement is demonstrated in the form of a dual-band photodiode with distinct near-infrared- and visible-light discrimination obtained via simple voltage control. The approach involves the monolithic stacking integration of methylammonium lead iodide (MAPbI3 ) and Si semiconductors, resulting in a p-Si/n-phenyl-C61 -butyric acid methyl ester/i-MAPbI3 /p-spiro-MeOTAD (PNIP) device. Remarkably, the PNIP configuration can independently detect the visible and near-infrared regions without traditional optical filters under a voltage range of 3 to -3 V. In addition, an imaging system for a prototype autonomous vehicle confirms the capability of the device to separate visible and near-infrared light via an electrical bias and practicality of this mechanism. Therefore, this study pushes the boundaries of image sensor development and sets the stage for fabricating compact and power-efficient photonic devices with superior performance and diverse functionality.

Template-Free Preparation of a Mesopore-Rich Hierarchically Porous Carbon Monolith from a Thermally Rearrangeable Polyurea Network.

A mesopore-rich, hierarchically porous carbon monolith was prepared by carbonizing a polyisocyanurate network derived by thermal rearrangement of a polyurea network. The initial polyurea network was synthesized by the cross-linking polymerization of tetrakis(4-aminophenyl)methane (TAPM) and hexamethylene diisocyanate (HDI) in the sol-forming condition, followed by precipitation into nanoparticulate solids in a nonsolvent. The powder was molded into a shape and then heated at 200-400 °C to obtain the porous carbon precursor composed of the rearranged network. The thermolysis of urea bonds to amine and isocyanate groups, the subsequent cyclization of isocyanates to isocyanurates, and the vaporization of volatiles caused sintering of the nanoparticles into a monolithic network with micro-, meso-, and macropores. The rearranged network was carbonized to obtain a carbon monolith. It was found that the rearranged network, with a high isocyanurate ratio, led to a porous carbon with a high mesopore ratio. The electrical conductivity of the resulting carbon monoliths exhibited a rapid response to carbon dioxide adsorption, indicating efficient gas transport through the hierarchical pore structure.

Perovskite multifunctional logic gates via bipolar photoresponse of single photodetector.

The explosive demand for a wide range of data processing has sparked interest towards a new logic gate platform as the existing electronic logic gates face limitations in accurate and fast computing. Accordingly, optoelectronic logic gates (OELGs) using photodiodes are of significant interest due to their broad bandwidth and fast data transmission, but complex configuration, power consumption, and low reliability issues are still inherent in these systems. Herein, we present a novel all-in-one OELG based on the bipolar spectral photoresponse characteristics of a self-powered perovskite photodetector (SPPD) having a back-to-back p+-i-n-p-p+ diode structure. Five representative logic gates ("AND", "OR", "NAND", "NOR", and "NOT") are demonstrated with only a single SPPD via the photocurrent polarity control. For practical applications, we propose a universal OELG platform of integrated 8 × 8 SPPD pixels, demonstrating the 100% accuracy in five logic gate operations irrelevant to current variation between pixels.

Omni-directional wind-driven triboelectric nanogenerator with cross-shaped dielectric film.

Triboelectric nanogenerators (TENGs) are actively being researched and developed to become a new external power unit for various electronics and applications. Wind is proposed as a mechanical energy source to flutter the dielectric film in wind-driven TENGs as it is clean, abundant, ubiquitous, and sustainable. Herein, we propose a TENG structure with dielectric films bent in four directions to collect the wind energy supply from all directions, unlike the conventional wind-driven TENGs which can only harvest the wind energy from one direction. Aluminum (Al) layer was intercalated within the dielectric film to improve electrostatic induction, resulting in improved triboelectric performances. Maximum open-circuit voltage (Voc) of 233 V, short-circuit current (Isc) of 348 µA, and output power density of 46.1 W m- 2 at an external load of 1 MΩ under a wind speed of 9 m s- 1 were revealed, and it faithfully lit "LED" characters composed of 25 LEDs.

Design of Chemically Stable Organic Perovskite Quantum Dots for Micropatterned Light-Emitting Diodes through Kinetic Control of a Cross-Linkable Ligand System.

Perovskite quantum dot (QD) light-emitting diodes (PeLEDs) are ideal for next-generation display applications because of their excellent color purity, high efficiency, and cost-effective fabrication. However, developing a technology for high-resolution multicolor patterning of perovskite QDs remains challenging, owing to the chemical instability of these materials. To overcome these issues, in this work, the generation of surface defects is prevented by controlling the ligand-binding kinetics using a stable ligand system (Stable LS). The crystalline reconstruction of perovskite QDs after addition of the Stable LS results in an ≈18% increase in their photoluminescence quantum yield in solution and it also improves the ambient stability of the perovskite QD solution. Moreover, the perovskite QDs with Stable LS can undergo cross-linking under UV irradiation. The tightly bridged perovskite QDs effectively prevent moisture-assisted ligand dissociation in film state due to the increased hydrophobicity and restricted movement of the cross-linked surface ligands. Thus, the cross-linked perovskite QD film shows improved chemical/environmental stability without substantial deterioration in optoelectrical properties. As a result, a white electroluminescent device with high resolution (≈1 µm) is successfully fabricated by inkjet printing using green and red perovskite QDs.

Sandwich-Doping for a Large Schottky Barrier and Long-Term Stability in Graphene/Silicon Schottky Junction Solar Cells.

Doping is an effective method for controlling the electrical properties and work function of graphene which can improve the power conversion efficiency of graphene-based Schottky junction solar cells (SJSCs). However, in previous approaches, the stability of chemical doping decreased over time due to the decomposition of dopants on the surface of graphene under ambient conditions. Here, we report an efficient and strong p-doping by simple sandwich doping on both the top and bottom surfaces of graphene. We confirmed that the work function of sandwich-doped graphene increased by 0.61 eV and its sheet resistance decreased by 305.8 Ω/sq, compared to those of the pristine graphene. Therefore, the graphene-silicon SJSCs that used sandwich-doped graphene had a power conversion efficiency of 10.02%, which was 334% higher than that (2.998%) of SJSCs that used pristine graphene. The sandwich-doped graphene-based silicon SJSCs had excellent long-term stability over 45 days without additional encapsulation.

Reactant/polymer hybrid films on p-n junction photodetectors for self-powered, non-invasive glucose biosensors.

The portability of electronic-based biosensors is limited because of the use of batteries and/or solutions containing reactants such as enzymes for assay, which limits the utility of such biosensors in point-of-care (POC) testing. In this study, we report on the development of a self-powered biosensor composed of only portable components: a reactant-containing poly (ethylene glycol) (PEG) film for the colorimetric assay, and a self-powered n-InGaZnO/p-Si photodetector. The PEG film containing enzymes and color-developing agents was formed on a glass slide by spin coating. The self-powered biosensor was fabricated by placing the hybrid film on the p-n junction photodetector, and applied in non-invasive glucose detection (salivary glucose). Injection of the target-containing solution dissolved the PEG that led to the release of enzymes and color-developing agents, resulting in a colorimetric assay. The colorimetric assay could attenuate the light reaching the photodetector, thus facilitating target concentration verification by measuring the photocurrent. Our self-powered biosensor has two main advantages: (i) all components of the biosensor are portable and (ii) dilution of target concentration is avoided as the reagents are in the PEG film. Therefore, the self-powered biosensor, without solution-phase components, could be highly beneficial for creating portable, sensitive biosensors for POC testing.

Molecular Sieve Based on a PMMA/ZIF-8 Bilayer for a CO-Tolerable H2 Sensor with Superior Sensing Performance.

Semiconductor sensors equipped with Pd catalysts are promising candidates as low-powered and miniaturized surveillance devices that are used to detect flammable hydrogen (H2) gas. However, the following issues remain unresolved: (i) a sluggish sensing speed at room temperature and (ii) deterioration of sensing performance caused by interfering gases, particularly, carbon monoxide (CO). Herein, a bilayer comprising poly(methyl methacrylate) (PMMA) and zeolitic imidazolate framework-8 (ZIF-8) is utilized as a molecular sieve for diode-type H2 sensors based on a Pd-decorated indium-gallium-zinc oxide film on a p-type silicon substrate. While the PMMA effectively blocks the penetration of CO gas molecules into the sensing entity, the ZIF-8 improves sensing performances by modifying the catalytic activity of Pd, which is preferable for splitting H2 and O2 molecules. Consequently, the bilayer-covered sensor achieves outstanding CO tolerance with superior sensing figures of merit (response/recovery times of <10 s and sensing response of >5000% at 1% H2).

Small extracellular vesicles from human adipose-derived stem cells attenuate cartilage degeneration.

Osteoarthritis (OA) is a chronic degenerative disease of articular cartilage that is the most common joint disease worldwide. Mesenchymal stem cells (MSCs) have been the most extensively explored for the treatment of OA. Recently, it has been demonstrated that MSC-derived extracellular vesicles (EVs) may contribute to the potential mechanisms of MSC-based therapies. In this study, we investigated the therapeutic potential of human adipose-derived stem cells EVs (hASC-EVs) in alleviating OA, along with the mechanism. EVs were isolated from the culture supernatants of hASCs by a multi-filtration system based on the tangential flow filtration (TFF) system. The isolated EVs were characterised using dynamic light scattering (DLS), transmission electron microscopy (TEM), nanoparticle tracking analysis (NTA) and flow cytometry analysis. The hASC-EVs not only promoted the proliferation and migration of human OA chondrocytes, but also maintained the chondrocyte matrix by increasing type Ⅱ collagen synthesis and decreasing MMP-1, MMP-3, MMP-13 and ADAMTS-5 expression in the presence of IL-1ß in vitro. Intra-articular injection of hASC-EVs significantly attenuated OA progression and protected cartilage from degeneration in both the monosodium iodoacetate (MIA) rat and the surgical destabilisation of the medial meniscus (DMM) mouse models. In addition, administration of hASC-EVs inhibited the infiltration of M1 macrophages into the synovium. Overall results suggest that the hASC-EVs should be considered as a potential therapeutic approach in the treatment of OA.

High-Performance Photovoltaic Hydrogen Sensing Platform with a Light-Intensity Calibration Module.

Although battery-free gas sensors (e.g., photovoltaic or triboelectric sensors) have recently appeared to resolve the power consumption issue of conventional chemiresistors, severe technical barriers still remain. Especially, their signals varying under ambient conditions such as light intensity restrict the utilization of these sensors. Insufficient sensing performances (low response and slow sensing rate) of previous battery-free sensors are also an obstacle for practical use. Herein, a photovoltaic hydrogen (H2)-sensing platform having constant sensing responses regardless of light conditions is demonstrated. The platform consists of two photovoltaic units: (1) a palladium (Pd)-decorated n-IGZO/p-Si photodiode covered with a microporous zeolitic imidazolate framework-8 (ZIF-8) film and (2) a device with the same configuration, but without the Pd catalyst as a reference to calibrate the base current of sensor (1). The platform after calibration yields accurate response values in real time regardless of unknown irradiance. Besides, the sensing performances (e.g., sensing response of 1.57 × 104% at 1% H2 with a response time <15 s) of our platform are comparable with those of the conventional resistive H2 sensors, which yield unprecedented results in photovoltaic H2 sensors.

Enhancement of Interfacial Adhesion Using Micro/Nanoscale Hierarchical Cilia for Randomly Accessible Membrane-Type Electronic Devices.

The recent technology of transfer printing using various membrane-type flexible/stretchable electronic devices can provide electronic functions to desirable objects where direct device fabrication is difficult. However, if the target surfaces are rough and complex, the capability of accommodating surface mismatches for reliable interfacial adhesion remains a challenge. Here, we demonstrate that newly designed nanotubular cilia (NTCs), vertically aligned underneath a polyimide substrate, significantly enhance interfacial adhesion. The tubular structure easily undergoes flattening and wrapping motions to provide a large conformal contact area, and the synergetic effect of the assembled cilia strengthens the overall adhesion. Furthermore, the hierarchical structure consisting of radially spread film-type cilia combined with vertically aligned NTCs in specific regions enables successful transfer printing onto very challenging surfaces such as stone, bark, and textiles. Finally, we successfully transferred a temperature sensor onto an eggshell and indium gallium zinc oxide-based transistors onto a stone with no electrical failure.

Gold nanocap-supported upconversion nanoparticles for fabrication of a solid-phase aptasensor to detect ochratoxin A.

Solid-phase, single-step biosensors are crucial for the development of portable, reusable, and convenient biosensors, otherwise known as point-of-care (POC) testing. Although high-performance single-step biosensors based on the principle of Förster resonance energy transfer (FRET) and using upconversion nanoparticles (UCNPs) functionalized with aptamers have been suggested as easy-to-use platforms, they lack portability and reusability when used for solution-phase biosensing. In this study, we describe a solid-phase, single-step aptasensor that showed higher performance than those of solution-phase aptasensors, as well as promising reusability. The solid-phase, single-step aptasensor was developed based on Au nanocap-supported UCNPs (Au/UCNPs), which were partially embedded in a solid substrate (e.g. polydimethylsiloxane, PDMS). The Au nanocaps allowed the UCNPs to emit upconverted light only from the restricted areas of the UCNPs, i.e., where they were not covered by the nanocaps and PDMS. Functionalization of an aptamer labeled with a quencher on the restricted area enabled the effective quenching of upconverted light from Au/UCNP via FRET after target (ochratoxin A, OTA) detection. The solid-phase, single-step aptasensor showed a linear range of 0.1-1000 ng mL-1 and limit of detection of 0.022 ng mL-1 within 30 min toward OTA. Furthermore, reusability of the solid-phase aptasensor was evaluated for three cycles of detection and regeneration, establishing its apparent reusability via heat treatment. Hence, such solid-phase, single-step aptasensors pave the path to the development of a portable and reusable biosensor platform for POC testing.

Plasmon enhanced up-conversion nanoparticles in perovskite solar cells for effective utilization of near infrared light.

As an alternative to silicon-based solar cells, organic-inorganic hybrid perovskite solar cells (PSCs) have attracted much attention and achieved a comparable power conversion efficiency (PCE) to silicon-based ones, although the perovskite materials can absorb only visible light. Hence, the challenge remains to enhance the PCE utilizing near infrared (NIR) light in the solar light spectrum. One of the easiest ways to utilize the NIR is to incorporate NIR active materials in PSCs such as up-conversion nanoparticles (UCNPs); however, such a stratergy is not simple to adopt in PSCs due to the inherent vurnerability of perovskite materials towards moisture. In this work, we present NIR-utilizing PSCs by locating UCNPs within the PSC structure by a simple dry transfer method. A maximum PCE of 15.56% was obtained in the case of PSC having the UCNPs located between the hole transport layer (HTL) and gold (Au) top electrode, which is an 8.4% enhancement compared to the cell without the UCNPs. This enhancement came from the combined effects of NIR light utilization and the surface plasmon resonance (SPR) phenomenon originating from the Au top electrode, which was interfacing the UCNPs.

Unusual Thermal Conductivity of Carbon Nanosheets with Self-Emerged Graphitic Carbon Dots.

The thermal conductivity (κ) of two-dimensional conducting and transparent carbon nanosheets (CNSs) prepared by a catalyst- and transfer-free process is calculated for the first time by the optothermal Raman technique. A systematic structural analysis of CNSs reveals that the thickness of polymer films affects the interaction between molecules and a Si wafer significantly, thus helping to determine the ratio of sp2 and sp3 bonding configurations of carbon (C) atoms in the CNS. Notably, the holding time of carbonization can realize a hierarchical structure with graphitic carbon dots emerging from the CNS through the rearrangement of carbon atoms, leading to the excellent κ value of 540 W/(m·K) at 310 K. It is demonstrated that an appropriate increase in carbonization time can be an effective approach for improving the ratio of sp2- to sp3-bonded C atoms in the CNS. The thermal conductivity of the CNS with the highest ratio of sp2- to sp3-bonded C atoms exhibits superior behavior and is comparable to that of reduced graphene oxide and supported graphene, respectively. Finally, when the CNS with the highest κ value of 540 W/(m·K) was applied to a heater as the heat-dissipating material, the heater showed the temperature decrease by 14 °C compared to the case without the CNS. The catalyst- and transfer-free approach for the synthesis of CNSs is highly desirable for use as heat sink materials or substrates with heat dissipation functions for extensively integrated electronic devices.

Single-molecule DNA visualization using AT-specific red and non-specific green DNA-binding fluorescent proteins.

The recent advances in the single cell genome analysis are generating a considerable amount of novel insights into complex biological systems. However, there are still technical challenges because each cell has a single copy of DNA to be amplified in most single cell genome analytical methods. In this paper, we present a novel approach to directly visualize a genomic map on a large DNA molecule instantly stained with red and green DNA-binding fluorescent proteins without DNA amplification. For this visualization, we constructed a few types of fluorescent protein-fused DNA-binding proteins: H-NS (histone-like nucleoid-structuring protein), DNA-binding domain of BRCA1 (breast cancer 1), high mobility group-1 (HMG), and lysine tryptophan (KW) repeat motif. Because H-NS and HMG preferentially bind A/T-rich regions, we combined A/T specific binder (H-NS-mCherry and HMG-mCherry as red color) and a non-specific complementary DNA binder (BRCA1-eGFP and 2(KW)2-eGFP repeat as green color) to produce a sequence-specific two-color DNA physical map for efficient optical identification of single DNA molecules.

Improvement of perovskite crystallinity by omnidirectional heat transfer via radiative thermal annealing.

As promising photo-absorbing materials for photovoltaics, organic-inorganic hybrid perovskite materials such as methylammonium lead iodide and formamidinium lead iodide, have attracted lots of attention from many researchers. Among the various factors to be considered for high power conversion efficiency (PCE) in perovskite solar cells (PSCs), increasing the grain size of perovskite is most important. However, it is difficult to obtain a highly crystalline perovskite film with large grain size by using the conventional hot-plate annealing method because heat is transferred unidirectionally from the bottom to the top. In this work, we presented radiative thermal annealing (RTA) to improve the structural and electrical properties of perovskite films. Owing to the omnidirectional heat transfer, swift and uniform nuclei formation was possible within the perovskite film. An average grain size of 500 nm was obtained, which is 5 times larger than that of the perovskite film annealed on a hot-plate. This perovskite film led to an enhancement of photovoltaic performance of PSCs. Both short-circuit current density and PCE of the PSCs prepared by RTA were improved by 10%, compared to those of PSCs prepared by hot-plate annealing.

Surface conversion of ZnO nanorods to ZIF-8 to suppress surface defects for a visible-blind UV photodetector.

ZnO nanomaterials are promising building blocks for an efficient UV photodetector; however, their slow sensing behavior and undesired response to visible light, which are attributed to surface defects, such as oxygen or zinc vacancies, are challenges that remain to be addressed. Here, we transformed the ZnO nanorod surface into a zeolitic imidazolate framework-8 (ZIF-8) to eliminate ZnO surface defects. Vertical-type photodetectors were fabricated incorporating a Schottky junction at the ZIF-8/gold (Au) top electrode and could respond to UV light with a rapid response and recovery (1-2 s) and demonstrated a UV-to-visible rejection ratio in the order of 103, qualifying them as efficient visible-blind UV photodetectors. It is noteworthy that the ZIF-8 layer effectively separated the photogenerated electron-hole pairs, and thus reduced their recombination probability. The enhanced photodetector displayed excellent figures-of-merit: a responsivity of 291 A W-1 and a detectivity of 5.9 × 1013 cm Hz1/2 W-1 under illumination at 295 nm.

Self-Powered Biosensors Using Various Light Sources in Daily Life Environments: Integration of p-n Heterojunction Photodetectors and Colorimetric Reactions for Biomolecule Detection.

Electronic biosensors operating without power supply are high in demand owing to increasing interest in point-of-care (POC) coupled with portable and wearable electronic devices for smart healthcare services. Although self-powered electronic sensors have emerged with the promise of resolving the energy supply problems, achieving sufficient sensitivity to targets in real samples is highly challenging because of the matrix effect caused by electroactive species. In this study, we developed a self-powered biosensor platform by combining n-indium gallium zinc oxide (IGZO)/p-Si heterojunction photodetectors and physically separated colorimetric reactions. The self-powered biosensors were applied to glucose detection in real human samples using light sources from daily life environments such as fluorescent light and sunlight. The sensors showed high sensitivity and stability from 0.01 to 10 mg mL-1 of glucose in human saliva and urine without matrix effect from the electroactive species in real samples. In addition, a small change in glucose concentration in human serum was distinguishable with a resolution of 0.01 mg mL-1. Notably, these results were obtained using well-developed and widely used materials like Si and IGZO with simple deposition techniques. Moreover, this self-powered biosensing platform can be universally applied for the detection of all biomolecules being detected by colorimetric assays. To the best of our knowledge, this is the first report on such self-powered biosensors, which could be a promising candidate for future POC biosensors integrated with portable and wearable electronic devices.

Polarization-sensitive tunable absorber in visible and near-infrared regimes.

A broadband tunable absorber is designed and fabricated. The tunable absorber is comprised of a dielectric-metal-dielectric multilayer and plasmonic grating. A large size of tunable absorber device is fabricated by nano-imprinting method. The experimental results show that over 90% absorption can be achieved within visible and near-infrared regimes. Moreover, the high absorption can be controlled by changing the polarization of incident light. This polarization-sensitive tunable absorber can have practical applications such as high-efficiency polarization detectors and transmissive polarizer.

Radial multi-quantum well ZnO nanorod arrays for nanoscale ultraviolet light-emitting diodes.

Since semiconducting ZnO has attractive properties such as wide bandgap and large exciton binding energy, it has motivated us to realize efficient ultraviolet (UV) light-emitting diodes (LEDs). Furthermore, facile growth of ZnO nanostructures has triggered numerous research studies to examine them as nanoscale building blocks for optoelectronic devices. Here, we demonstrate the growth of ZnO-based core-shell p-n homojunction nanorod arrays with radial MgZnO/ZnO multiple quantum wells (MQWs) and report the characteristics of a core-shell ZnO nanorod LED. The shell layers of MgZnO/ZnO MQWs and p-type antimony-doped MgZnO were epitaxially grown on the surface of ZnO core nanorod arrays. By introducing the radial MQWs, the photoluminescence intensity was greatly increased by 4 times, compared to that of the bare ZnO nanorod array, suggesting that the core-shell MQWs can be used to realize the nanoscale ZnO LEDs with high internal quantum efficiency. As the injection current increased, the EL intensity of UV emission at 375 nm from the MgZnO/ZnO MQWs strongly increased without shifting of the emission peak because of the non-polar nature of MQWs grown on the side walls of the ZnO nanorods. These results highlight the potential of an integrated nanoscale UV light emitter in various photonic devices.