A new Schottky junction ultraviolet photodetector (UVPD) is fabricated by coating a free‐standing ZnO nanorod (ZnONR) array with a layer of transparent monolayer graphene (MLG) film. The ...single‐crystalline 0001‐oriented ZnONR array has a length of about 8–11 μm, and a diameter of 100∼600 nm. Finite element method (FEM) simulation results show that this novel nanostructure array/MLG heterojunction can trap UV photons effectively within the ZnONRs. By studying the I–V characteristics in the temperature range of 80–300 K, the barrier heights of the MLG film/ZnONR array Schottky barrier are estimated at different temperatures. Interestingly, the heterojunction diode with typical rectifying characteristics exhibits a high sensitivity to UV light illumination and a quick response of millisecond rise time/fall times with excellent reproducibility, whereas it is weakly sensitive to visible light irradiation. It is also observed that this UV photodetector (PD) is capable of monitoring a fast switching light with a frequency as high as 2250 Hz. The generality of the above results suggest that this MLG film/ZnONR array Schottky junction UVPD will have potential application in future optoelectronic devices.
A new Schottky junction ultraviolet photodetector is fabricated by coating a free‐standing ZnO nanorod array with a monolayer graphene film. This special structure is able to trap UV light within ZnO nanorods, and exhibits high sensitivity to UV light irradiation with good reproducibility and fast response time.
The conformational distribution and mutual interconversion of thermally activated delayed fluorescence (TADF) emitters significantly affect the exciton utilization. However, their influence on the ...photophysics in amorphous film states is still not known due to the lack of a suitable quantitative analysis method. Herein, we used temperature‐dependent time‐resolved photoluminescence spectroscopy to quantitatively measure the relative populations of the conformations of a TADF emitter for the first time. We further propose a new concept of “self‐doping” for realizing high‐efficiency nondoped OLEDs. Interestingly, this “compositionally” pure film actually behaves as a film with a dopant (quasi‐equatorial form) in a matrix (quasi‐axial form). The concentration‐induced quenching that may occur at high concentrations is thus expected to be effectively relieved. The “self‐doping” OLED prepared with the newly developed TADF emitter TP2P‐PXZ as a neat emitting layer realizes a high maximum external quantum efficiency of 25.4 % and neglectable efficiency roll‐off.
Until now, the influence of the conformational distribution on the photophysics and device performance of thermally activated delayed fluorescence (TADF) emitters has not been clear. Herein, conformational populations in disordered solid states are quantitatively measured for the first time. A high‐performance “self‐doping” OLED with a maximum external quantum efficiency of 25.4 % is achieved.
Single‐crystalline silicon (sc‐Si) is the dominant semiconductor material for the modern electronics industry. Despite their excellent photoelectric and electronic properties, the rigidity, ...brittleness, and nontransparency of commonly used silicon wafers limit their application in transparent flexible optoelectronics. In this study, a new type of Si microstructure, named single‐crystalline Si frameworks (sc‐SiFs), is developed, through a combination of wet‐etching and microfabrication technologies. The sc‐SiFs are self‐supported, flexible, lightweight, tailorable, and highly transparent. They can withstand a small bending radius of less than 0.5 mm and have a transparency of up to 96% in all wavelength ranges, owing to the hollowed‐out framework structures. Thus, the sc‐SiFs provide a new platform for high‐performance transparent flexible optoelectronics. Taking transparent flexible photodetectors (TFPDs) as an example, substrate‐free and self‐driven TFPDs are achieved based on the sc‐SiFs. The devices exhibit superior performance compared to other reported TFPDs and reveal the great potential for integrated optoelectronic applications. The development of sc‐SiFs paves the way toward the fabrication of high‐performance transparent flexible devices for a host of applications, including e‐skins, the Internet of Things, transparent flexible displays, and artificial visual cortexes.
Self‐supported, flexible, and highly transparent single‐crystalline silicon frameworks (sc‐SiFs) are fabricated from commonly used Si wafers by combining wet‐etching and microfabrication technologies. They provide a new platform for transparent flexible optoelectronics, enabling the construction of high‐performance transparent flexible Si‐based devices.
A facile fabricating method has been established for large-area uniform silicon nanowires arrays. All silicon nanowires obtained were single crystals and epitaxial on the substrate. Six kinds of ...silicon wafers with different types, surface orientations, and doping levels were utilized as starting materials. With the catalysis of silver nanoparticles, room-temperature mild chemical etching was conducted in aqueous solution of hydrofluoric acid (HF) and hydrogen peroxide (H2O2). The corresponding silicon nanowires arrays with different morphologies were obtained. The silicon nanowires possess the same type and same doping level of the starting wafer. All nanowires on the substrate have the same orientation. For instance, both (100)- and (111)-oriented p-type wafers produced silicon nanowires in the (100) direction. For every kind of silicon wafer, the effect of etching conditions, such as components of etchant, temperature, and time, were systemically investigated. This is an appropriate method to produce a large amount of silicon nanowires with defined type, doping level, and growth direction for industrial applications.
Nondoped organic light‐emitting diodes (OLEDs) have drawn enormous attention for their merits of process simplicity, reduced fabrication cost, and phase stability. Herein, a novel approach of ...utilizing intermolecular hydrogen bonding for enhancing performance of nondoped OLEDs with a new thermally activated delayed fluorescence (TADF) emitter 10‐(4‐(2,6‐di(pyrimidin‐5‐yl)pyridin‐4‐yl)phenyl)‐10H‐phenoxazine (DPmP‐PXZ) is investigated. Endowing with suitable intermolecular hydrogen bonds linking the ends of neighboring DPmP‐PXZ molecules, the molecules tend to form extended 1D molecular chain in solid. This 1D structure effectively keeps the electron‐rich PXZ cores in neighboring molecules apart from each other such that triplet‐related exciton quenching can be well suppressed. In addition, it also improves the balance of carrier mobilities and the optical out‐coupling from the emitting layer. With these merits, OLEDs using DPmP‐PXZ as a dopant emitter, from 10 to 100 wt%, can maintain high external quantum efficiencies (EQEs) of over 20%. More importantly, its nondoped OLED shows a yellow emission and an excellent maximum EQE of 21.8% with little efficiency roll‐off which is even comparable with state‐of‐the‐art yellow OLEDs. These results provide new insight on the role of hydrogen bonding in molecular packing and its subsequent influences on the performance of OLEDs.
Suitable intermolecular hydrogen bonding interactions of 10‐(4‐(2,6‐di(pyrimidin‐5‐yl)pyridin‐4‐yl)phenyl)‐10H‐phenoxazine (DPmP‐PXZ) enable the formation of 1D directional supramolecular extension, which not only effectively restricts the triplet‐related exciton quenching, but also balances the carrier mobilities and favors high out‐coupling efficiency. Thus, the organic light‐emitting diodes (OLEDs) using DPmP‐PXZ as the dopant maintain high external quantum efficiencies (EQEs) of over 20% with neglectable concentration quenching effect.
Silicon nanowire (SiNW) fabrics are of great interest for fabricating high-performance multifunctional wearable sensors. However, it remains a big challenge to fabricate high-quality SiNW fabrics in ...a simple and efficient manner. Here we report, for the first time, one-step growth of large-area SiNW fabrics for multifunctional wearable sensors, by using a massive metal-assisted chemical vapor deposition (CVD) method. With bulk Sn as a catalyst source, numerous millimeter-long SiNWs grow and naturally interweave with each other, forming SiNW fabrics over 80 cm
2
in one experiment. In addition to intrinsic electronic properties of Si materials, the SiNW fabrics also feature high flexibility, good tailorability and light weight, rendering them ideal for fabricating multifunctional wearable sensors. The prototype sensors based on the SiNW fabrics could effectively detect various stimuli including temperature, light, strain and pressure, with outstanding performance among reported multifunctional sensors. We further demonstrate the integration of the prototype sensors onto the body of a robot, enabling its perception to various environmental stimuli. The ability to prepare high-quality SiNW fabrics in a simple and efficient manner will stimulate the development of wearable devices for applications in portable electronics, Internet of Things, health care and robotics.
We present an ultrasensitive ultraviolet （UV） detector based on a p-type ZnS nanoribbon （NR）/indium tin oxide （ITO） Schottky barrier diode （SBD）. The device exhibits a pseudo-photovoltaic behavior ...which can allow the SBD to detect UV light irradiation with incident power of 6 × 10^-17 W （-85 photons/s on the NR） at room temperature, with excellent reproducibility and stability. The corresponding detectivity and photoconductive gain are calculated to be 3.1 × 10^20 cm.Hz1/2.W^-1 and 6.6 × 10^5, respectively. It is found that the presence of the trapping states at the p-ZnS NWITO interface plays a crucial role in determining the ultrahigh sensitivity of this nanoSBDs. Based on our theoretical calculation, even ultra-low photon fluxes on the order of several tens of photons could induce a significant change in interface potential and consequently cause a large photocurrent variation. The present study provides new opportunities for developiphigh-performance optoelectronic devices in the future.
The elongation of free-standing one-dimensional (1D) functional nanostructures into lengths above the millimeter range has brought new practical applications as they combine the remarkable properties ...of nanostructured materials with macroscopic lengths. However, it remains a big challenge to prepare 1D silicon nanostructures, one of the most important 1D nanostructures, with lengths above the millimeter range. Here we report the unprecedented preparation of ultralong single-crystalline Si nanowires with length up to 2 cm, which can function as the smallest active material to facilitate the miniaturization of macroscopic devices. These ultralong Si nanowires with augmented flexibility are of emerging interest for flexible electronics. We also demonstrate the first single-nanowire-based wearable joint motion sensor with superior performance to reported systems, which just represents one example of novel devices that can be built from these nanowires. The preparation of ultralong Si nanowires will stimulate the fabrication and miniaturization of electric, optical, medical, and mechanical devices to impact the semiconductor industry and our daily life in the near future.
Well‐aligned ZnO nanowires (NWs) with tunable n‐type conductivity are synthesized by introducing Ga2O3 as a dopant source in thermal evaporation. The crystallographic orientation of the NWs depends ...on the dopant content. Electrical transport property measurements on single nanowires verify that the resistivity of ZnO NWs can be controlled, with high reproducibility, by the Ga impurities.
