Ultrasensitive UV Photodetector Based on Interfacial Charge-Controlled Inorganic Perovskite-Polymer Hybrid Structure.

In this work, we demonstrate an ultrasensitive, visible-blind ultraviolet (UV) photodetector based on perovskite-polymer hybrid structure. A novel wide-band-gap vacancy-ordered lead-free inorganic perovskite Cs2SnCl6 with Nd3+ doping is employed in the active layer of this hybrid photodetector. Remarkably, with interfacial charge-controlled hole-injection operating mechanism, our device achieves a maximum detectivity of 6.3 × 1015 Jones at 372 nm, fast photoresponse speed with rise time and fall time in the order of milliseconds, and a large linear dynamic range of 118 dB. The performance is significantly better than most of the existing organic and inorganic semiconductor UV photodetectors reported so far, and its detectivity is close to 1 order of magnitude higher than that of the photomultiplication tube (PMT) in the UV region. In addition, the photodetector demonstrated excellent environmental stability, which is critical for commercial deployment of perovskite-based optoelectronic devices. The results presented in this work open a new route toward development of high-performance optoelectronic devices using perovskite-based hybrid nanomaterial systems.

Synthesis and characterization of molybdenum disulfide nanoparticles in Shewanella oneidensis MR-1 biofilms.

Shewanella oneidensis MR-1 is a dissimilatory metal-reducing bacterium capable of reducing various metal and sulfur compounds and precipitating them in nanoparticulate form. Here, we report the synthesis of molybdenum disulfide nanomaterials at the site of S. oneidensis biofilms grown in the presence of molybdenum trioxide and sodium thiosulfate. Samples from the growth medium were imaged using scanning electron microscopy and characterized using transmission electron microscopy, energy-dispersive x-ray spectroscopy, absorbance spectroscopy, and x-ray diffraction. These methods revealed the presence of molybdenum disulfide nanoparticle aggregates 50-300 nm in diameter with both hexagonal and rhombohedral polytypes. As a biosynthesis method for molybdenum sulfide, the use of S. oneidensis offers the advantage of significantly reduced heat and chemical solvent input compared to conventional methods of synthesizing molybdenum disulfide nanoparticles.

Cl-Doped ZnO Nanowire Arrays on 3D Graphene Foam with Highly Efficient Field Emission and Photocatalytic Properties.

An environmentally friendly, low-cost, and large-scale method is developed for fabrication of Cl-doped ZnO nanowire arrays (NWAs) on 3D graphene foam (Cl-ZnO NWAs/GF), and investigates its applications as a highly efficient field emitter and photocatalyst. The introduction of Cl-dopant in ZnO increases free electrons in the conduction band of ZnO and also leads to the rough surface of ZnO NWAs, which greatly improves the field emission properties of the Cl-ZnO NWAs/GF. The Cl-ZnO NWAs/GF demonstrates a low turn-on field (≈1.6 V µm(-1)), a high field enhancement factor (≈12844), and excellent field emission stability. Also, the Cl-ZnO NWAs/GF shows high photocatalytic efficiency under UV irradiation, enabling photodegradation of organic dyes such as RhB within ≈75 min, with excellent recyclability. The excellent photocatalytic performance of the Cl-ZnO NWAs/GF originates from the highly efficient charge separation efficiency at the heterointerface of Cl-ZnO and GF, as well as improved electron transport efficiency due to the doping of Cl. These results open up new possibilities of using Cl-ZnO and graphene-based hybrid nanostructures for various functional devices.

Organic-Inorganic Heterointerfaces for Ultrasensitive Detection of Ultraviolet Light.

The performance of graphene field-effect transistors is limited by the drastically reduced carrier mobility of graphene on silicon dioxide (SiO2) substrates. Here we demonstrate an ultrasensitive ultraviolet (UV) phototransistor featuring an organic self-assembled monolayer (SAM) sandwiched between an inorganic ZnO quantum dots decorated graphene channel and a conventional SiO2/Si substrate. Remarkably, the room-temperature mobility of the chemical-vapor-deposition grown graphene channel on the SAM is an order-of-magnitude higher than on SiO2, thereby drastically reducing electron transit-time in the channel. The resulting recirculation of electrons (in the graphene channel) within the lifetime of the photogenerated holes (in the ZnO) increases the photoresponsivity and gain of the transistor to ∼10(8) A/W and ∼3 × 10(9), respectively with a UV to visible rejection ratio of ∼10(3). Our UV photodetector device manufacturing is also compatible with current semiconductor processing, and suitable for large volume production.

Flexible, thorn-like ZnO-multiwalled carbon nanotube hybrid paper for efficient ultraviolet sensing and photocatalyst applications.

We report fabrication of a flexible, thorn-like ZnO-multiwalled carbon nanotube (MWCNT) hybrid paper with high aspect ratio for efficient ultraviolet (UV) sensing and photocatalyst applications. The thorn-like ZnO-MWCNT hybrid paper was synthesized via atomic layer deposition (ALD) of a uniform ZnO thin film on the outside surface of the MWCNT followed by hydrothermal growth of ZnO branches. The hybrid paper achieved very high surface to volume ratio, which is favorable for photodetector and photocatalyst applications. A photodetector fabricated from the hybrid paper demonstrates a high sensitivity to UV light with a maximum photoresponsivity of 45.1 A W(-1) at 375 nm, corresponding to an external quantum efficiency as high as 14927%. The rise time and fall time of the UV photodetector are 29 ms and 33 ms, respectively, indicating fast transient response characteristics for the device. The high photoresponsivity and fast transient response are attributed to efficient carrier transport and collection efficiency of the hybrid paper. Besides, the thorn-like ZnO-MWCNT hybrid paper demonstrates excellent photocatalytic performance under UV irradiation, enabling photo-degradation of organic dyes such as Rhodamine B (RhB) within 90 minutes, with good recyclability.

High-performance ultraviolet photodetector based on organic-inorganic hybrid structure.

An ultraviolet (UV) photodetector is fabricated by sandwiching a nanocomposite active layer between charge-selective semiconducting polymers. The nanocomposite active layer composed of TiO2 nanoparticles (NPs) blended with 1,3-bis(N-carbazolyl)benzene (mCP), which acts as a "valve" controller that enables hole injection into the device upon UV illumination. The UV photodetector demonstrated a high photocurrent to dark current ratio (∼10(4)), a large linear dynamic range of 60 dB, and a remarkable external quantum efficiency (∼8.5 × 10(4)%) for the UV light at 351 nm. In addition to discussing the performance of the UV photodetector, a general strategy for design and fabrication of high-performance UV photodetectors with hole injection operation mode is suggested.

An ultraviolet photodetector fabricated from WO3 nanodiscs/reduced graphene oxide composite material.

A high sensitivity, fast ultraviolet (UV) photodetector was fabricated from WO3 nanodiscs (NDs)/reduced graphene oxide (RGO) composite material. The WO3 NDs/reduced GO composite material was synthesized using a facile three-step synthesis procedure. First, the Na2WO4/GO precursor was synthesized by homogeneous precipitation. Second, the Na2WO4/GO precursor was transformed into Na2WO4/GO composites by acidification. Finally, the Na2WO4/GO composites were reduced to WO3 NDs/RGO via a hydrothermal reduction process. The UV photodetector showed a fast transient response and high responsivity, which are attributed to the improved carrier transport and collection efficiency through graphene. The excellent material properties of the WO3 NDs/RGO composite demonstrated in this work may open up new possibilities for using WO3 NDs/RGO for future optoelectronic applications.

High responsivity, fast ultraviolet photodetector fabricated from ZnO nanoparticle-graphene core-shell structures.

We report a simple, efficient and versatile method for assembling metal oxide nanomaterial-graphene core-shell structures. An ultraviolet photodetector fabricated from the ZnO nanoparticle-graphene core-shell structures showed high responsivity and fast transient response, which are attributed to the improved carrier transport efficiency arising from graphene encapsulation.

Heterojunction photodiode fabricated from hydrogen treated ZnO nanowires grown on p-silicon substrate.

A heterojunction photodiode was fabricated from ZnO nanowires (NWs) grown on a p-type Si (100) substrate using a hydrothermal method. Post growth hydrogen treatment was used to improve the conductivity of the ZnO NWs. The heterojunction photodiode showed diode characteristics with low reverse saturation current (5.58 × 10(-7) A), relatively fast transient response, and high responsivity (22 A/W at 363 nm). Experiments show that the photoresponsivity of the photodiode is dependent on the polarity of the voltages. The photoresponsivity of the device was discussed in terms of the band diagrams of the heterojunction and the carrier diffusion process.

Enhanced ultraviolet emission from poly(vinyl alcohol) ZnO nanoparticles using a SiO2-Au core/shell structure.

Enhanced near band gap edge (NBE) emissions of PVA-ZnO nanoparticles were achieved by employing SiO(2)-Au core/shell nanostructures whereas the defect-level emission (DLE) is greatly suppressed. A maximum enhancement of nearly 400% was observed using SiO(2)-Au for the emission with optical resonance at 554 nm. SiO(2)-Au core/shell nanostructures also show a superior tunability of resonance energy as compared to that of the pure metal nanoparticles. The enhancement of the NBE emission and suppressed DLE is ascribed to the transfer of the energetic electrons excited by surface plasmon from metal nanoparticles to the conduction band of ZnO nanoparticles.