Two-Dimensional Bis(dithiolene)iron(II) Self-Powered UV Photodetectors with Ultrahigh Air Stability.
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ABSTRACT: Organometallic two-dimensional (2D) nanosheets with tailorable components have recently fascinated the optoelectronic communities due to their solution-processable nature. However, the poor stability of organic molecules may hinder their practical application in photovoltaic devices. Instead of conventional organometallic 2D nanosheets with low weatherability, an air-stable π-conjugated 2D bis(dithiolene)iron(II) (FeBHT) coordination nanosheet (CONASH) is synthesized via bottom-up liquid/liquid interfacial polymerization using benzenehexathiol (BHT) and iron(II) ammonium sulfate [Fe(NH4)2(SO4)2] as precursors. The uncoordinated thiol groups in FeBHT are easily oxidized, but the Fe(NH4)2(SO4)2 dissociation rate is slow, which facilitates the protection of sulfur groups by iron(II) ions. The density functional theory calculates that the resultant FeBHT network gains the oxygen-repelling function for oxidation suppression. In air, the FeBHT CONASH exhibits self-powered photoresponses with short response times (<40 ms) and a spectral responsivity of 6.57 mA W-1, a specific detectivity of 3.13 × 1011 Jones and an external quantum efficiency of 2.23% under 365 nm illumination. Interestingly, the FeBHT self-powered photodetector reveals extremely high long-term air stability, maintaining over 94% of its initial photocurrent after aging for 60 days without encapsulation. These results open the prospect of using organometallic 2D materials in commercialized optoelectronic fields.
Project description:Modern biomedical studies have yielded abundant survival data with high-throughput predictors. Variable screening is a crucial first step in analyzing such data, for the purpose of identifying predictive biomarkers, understanding biological mechanisms, and making accurate predictions. To nonparametrically quantify the relevance of each candidate variable to the survival outcome, we propose integrated powered density (IPOD), which compares the differences in the covariate-stratified distribution functions. The proposed new class of statistics, with a flexible weighting scheme, is general and includes the Kolmogorov statistic as a special case. Moreover, the method does not rely on rigid regression model assumptions and can be easily implemented. We show that our method possesses sure screening properties, and confirm the utility of the proposal with extensive simulation studies. We apply the method to analyze a multiple myeloma study on detecting gene signatures for cancer patients' survival.
Project description:Two-dimensional (2D) transition-metal monochalcogenides have been recently predicted to be potential photo(electro)catalysts for water splitting and photoelectrochemical (PEC) reactions. Differently from the most established InSe, GaSe, GeSe, and many other monochalcogenides, bulk GaS has a large band gap of ∼2.5 eV, which increases up to more than 3.0 eV with decreasing its thickness due to quantum confinement effects. Therefore, 2D GaS fills the void between 2D small-band-gap semiconductors and insulators, resulting of interest for the realization of van der Waals type-I heterojunctions in photocatalysis, as well as the development of UV light-emitting diodes, quantum wells, and other optoelectronic devices. Based on theoretical calculations of the electronic structure of GaS as a function of layer number reported in the literature, we experimentally demonstrate, for the first time, the PEC properties of liquid-phase exfoliated GaS nanoflakes. Our results indicate that solution-processed 2D GaS-based PEC-type photodetectors outperform the corresponding solid-state photodetectors. In fact, the 2D morphology of the GaS flakes intrinsically minimizes the distance between the photogenerated charges and the surface area at which the redox reactions occur, limiting electron-hole recombination losses. The latter are instead deleterious for standard solid-state configurations. Consequently, PEC-type 2D GaS photodetectors display a relevant UV-selective photoresponse. In particular, they attain responsivities of 1.8 mA W-1 in 1 M H2SO4 [at 0.8 V vs reversible hydrogen electrode (RHE)], 4.6 mA W-1 in 1 M Na2SO4 (at 0.9 V vs RHE), and 6.8 mA W-1 in 1 M KOH (at 1.1. V vs RHE) under 275 nm illumination wavelength with an intensity of 1.3 mW cm-2. Beyond the photodetector application, 2D GaS-based PEC-type devices may find application in tandem solar PEC cells in combination with other visible-sensitive low-band-gap materials, including transition-metal monochalcogenides recently established for PEC solar energy conversion applications.
Project description:It has been a universal route for enhanced photoelectric performance in photodetectors by constructing a heterojunction that is conductive for suppressing recombination of photogenerated carriers and promoting collection efficiency, and probably producing self-powered capability. However, the dependence of the built-in electric field distributions created by the heterojunction on photodetector performance has rarely been investigated. Herein, two kinds of self-powered UV-visible photodetectors with different device architectures based on single Se wire and CsPbBr3 particles are facilely fabricated and compared. It is found that both the two photodetectors show excellent self-powered operating properties, fast response and binary response. However, due to the different distributions of built-in electric field caused by device architectures, it yields a significant photovoltaic voltage distinction and different responsivity and detectivity spectra for the Se/CsPbBr3 photodetectors. These results are conductive to guide the design of self-powered heterojunction photodetectors by regulating the built-in electric field distributions.
Project description:Molybdenum disulfide (MoS2) has been attracting considerable attention due to its excellent electrical and optical properties. We successfully grew high-quality, large-area and uniform few-layer (FL)-MoS2 on p-doped gallium nitride (p-GaN) using a simplified sulfurization technique by the single-zone CVD of a Mo seed layer via E-beam evaporation. Tuning the sulfurization parameters, namely temperature and duration, has been discovered to be an effective strategy for improving MoS2 orientation (horizontally aligned and vertically aligned) and quality, which affects photodetector (PD) performance. The increase in the sulfurization temperature to 850 °C results in improved structural quality and crystallite size. However, a prolonged sulfurization duration of 60 minutes caused the degradation of the film quality. The close lattice match between p-GaN and MoS2 contributes to the excellent quality growth of deposited MoS2. Following this, an n-MoS2/p-GaN heterostructure PD was successfully built by a MoS2 position-selectivity method. We report a highly sensitive and self-powered GaN/MoS2 p-n heterojunction PD with a relatively high responsivity of 14.3 A W-1, a high specific detectivity of 1.12 × 1013 Jones, and a fast response speed of 8.3/13.4 μs (20 kHz) under a UV light of 355 nm at zero-bias voltage. Our PD exhibits superior performance to that of the previously reported MoS2/GaN p-n PD. Our findings suggest a more efficient and straightforward approach to building high-performance self-powered UV PDs.
Project description:Due to its high carrier mobility, broadband absorption, and fast response time, the semi-metallic graphene is attractive for optoelectronics. Another two-dimensional semiconducting material molybdenum disulfide (MoS2) is also known as light- sensitive. Here we show that a large-area and continuous MoS2 monolayer is achievable using a CVD method and graphene is transferable onto MoS2. We demonstrate that a photodetector based on the graphene/MoS2 heterostructure is able to provide a high photogain greater than 10(8). Our experiments show that the electron-hole pairs are produced in the MoS2 layer after light absorption and subsequently separated across the layers. Contradictory to the expectation based on the conventional built-in electric field model for metal-semiconductor contacts, photoelectrons are injected into the graphene layer rather than trapped in MoS2 due to the presence of a perpendicular effective electric field caused by the combination of the built-in electric field, the applied electrostatic field, and charged impurities or adsorbates, resulting in a tuneable photoresponsivity.
Project description:Photodetectors that are intimately interfaced with human skin and measure real-time optical irradiance are appealing in the medical profiling of photosensitive diseases. Developing compliant devices for this purpose requires the fabrication of photodetectors with ultraviolet (UV)-enhanced broadband photoresponse and high mechanical flexibility, to ensure precise irradiance measurements across the spectral band critical to dermatological health when directly applied onto curved skin surfaces. Here, a fully 3D printed flexible UV-visible photodetector array is reported that incorporates a hybrid organic-inorganic material system and is integrated with a custom-built portable console to continuously monitor broadband irradiance in-situ. The active materials are formulated by doping polymeric photoactive materials with zinc oxide nanoparticles in order to improve the UV photoresponse and trigger a photomultiplication (PM) effect. The ability of a stand-alone skin-interfaced light intensity monitoring system to detect natural irradiance within the wavelength range of 310-650 nm for nearly 24 h is demonstrated.
Project description:The nanoplasmonic impact of chemically synthesized Au nanoparticles (Au NPs) on the performance of GaN nanostructure-based ultraviolet (UV) photodetectors is analyzed. The devices with uniformly distributed Au NPs on GaN nanostructures (nanoislands and nanoflowers) prominently respond toward UV illumination (325 nm) in both self-powered as well as photoconductive modes of operation and have shown fast and stable time-correlated response with significant enhancement in the performance parameters. A comprehensive analysis of the device design, laser power, and bias-dependent responsivity and response time is presented. The fabricated Au NP/GaN nanoflower-based device yields the highest photoresponsivity of ? 380 mA/W, detectivity of ? 1010 jones, reduced noise equivalent power of ? 5.5 × 10-13 W Hz-1/2, quantum efficiency of ? 145%, and fast response/recovery time of ?40 ms. The report illustrates the mechanism where light interacts with the chemically synthesized nanoparticles guided by the surface plasmon to effectively enhance the device performance. It is observed that the Au NP-stimulated local surface plasmon resonance effect and reduced channel resistance contribute to the augmented performance of the devices. Further, the decoration of low-dimensional Au NPs on GaN nanostructures acts as a detection enhancer with a fast recovery time and paves the way toward the realization of energy-efficient optoelectronic device applications.
Project description:Nitrogen-functionalized graphene quantum dots (NGQDs) are attractive building blocks for optoelectronic devices because of their exceptional tunable optical absorption and fluorescence properties. Here, we developed a high-performance flexible NGQD/graphene field-effect transistor (NGQD@GFET) hybrid ultraviolet (UV) photodetector, using dimethylamine-functionalized GQDs (NMe2-GQDs) with a large bandgap of ca. 3.3?eV. The NMe2-GQD@GFET photodetector exhibits high photoresponsivity and detectivity of ca. 1.5?×?104?A?W-1 and ca. 5.5?×?1011 Jones, respectively, in the deep-UV region as short as 255?nm without application of a backgate voltage. The feasibility of these flexible UV photodetectors for practical application in flame alarms is also demonstrated.
Project description:Low-cost, easily integrable photodetectors (PDs) for silicon (Si) photonics are still a bottleneck for photonic-integrated circuits (PICs), especially for wavelengths above 1.8 μm. Multilayered platinum diselenide (PtSe2) is a semi-metallic two-dimensional (2D) material that can be synthesized below 450 °C. We integrate PtSe2-based PDs directly by conformal growth on Si waveguides. The PDs operate at 1550 nm wavelength with a maximum responsivity of 11 mA/W and response times below 8.4 μs. Fourier-transform IR spectroscopy in the wavelength range from 1.25 to 28 μm indicates the suitability of PtSe2 for PDs far into the IR wavelength range. Our PtSe2 PDs integrated by direct growth outperform PtSe2 PDs manufactured by standard 2D layer transfer. The combination of IR responsivity, chemical stability, selective and conformal growth at low temperatures, and the potential for high carrier mobility makes PtSe2 an attractive 2D material for optoelectronics and PICs.
Project description:A self-powered ultraviolet (UV) photodetector (PD) based on p-NiO and n-ZnO was fabricated using low-temperature sputtering technique on indium doped tin oxide (ITO) coated plastic polyethylene terephthalate (PET) substrates. The p-n heterojunction showed very fast temporal photoresponse with excellent quantum efficiency of over 63% under UV illumination at an applied reverse bias of 1.2 V. The engineered ultrathin Ti/Au top metal contacts and UV transparent PET/ITO substrates allowed the PDs to be illuminated through either front or back side. Morphology, structural, chemical and optical properties of sputtered NiO and ZnO films were also investigated.