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Introducing nanostructures into bulk thermoelectric materials is an effective strategy for reducing lattice thermal conductivity (κlat). However, large numbers of hanging bonds emerge on account of lattice mismatch usually at the interfaces between nanostructures and matrix, thereby significantly deteriorating carrier mobility (µH) and seriously limiting thermoelectric performance. Here, utilizing the cointroduction of Gd‐Cu2Te into n‐type PbSe as a paradigm, the zT could be greatly improved. The conduction band flattening caused by Gd doping can successfully compensate for the small Seebeck coefficient in n‐type PbSe, thus achieving extraordinary electrical performance. Further advanced electron microscopy and X‐ray absorption fine structure spectra directly demonstrate that most of the Cu forms nanoscale Cu2Se precipitates, especially a unique semi‐coherent interface between the PbSe matrix and the Cu2Se nanoprecipitate is observed for the first time. Such nanoprecipitate accompanied by the semi‐coherent interface not only ensures higher µH as an excellent charge transfer mediator but also collectively scatters the heat‐carrying phonons over a wide frequency range to obtain the ultralow κlat, resulting in the prominent improvement of the ratio µH/κlat. The present finding represents an important step forward in electron–phonon decoupling via constructing semi‐coherent nanostructure and interface engineering, which should be applicable for other thermoelectric materials. [ABSTRACT FROM AUTHOR]

Abstract: Inversion symmetry broken 3R phase semiconducting transition metal dichalcogenides (TMDC) have huge potential applications in many novel fields, such as valleytronics and nonlinear optics for the strong spin–orbit coupling and particularly the persistent noncentrosymmetric structure regardless the layer numbers, in stark contrast to the strict layer number requirement in other phases. Unfortunately, the fabrication of 3R phase TMDC is still a huge task to date. Molybdenum telluride (MoTe2) attracts increasing interest in recent years due to the easy transition between its various phases and its narrow bandgap close to silicon. However, the weak Mo–Te bond and the small energy imparity among phases make it a big challenge to obtain pure‐phase single crystalline MoTe2, especially; it is still a virgin land to obtain two‐dimensional (2D) 3R‐MoTe2. Here, by rational controlling the deposition temperature and tellurization velocity, for the first time high quality 2D 3R‐MoTe2 flakes are synthesized via chemical vapor deposition from a MoCl5 precursor. Scanning transmission electron microscopy unambiguously reveals the 3R stacking mode of as‐synthesized MoTe2. Second harmonic generation measurement confirms the excellent odd/even layer‐independent frequency conversion efficiency. Besides, the outstanding intrinsic infrared detection ability of as‐synthesized 3R‐MoTe2 is demonstrated as well. [ABSTRACT FROM AUTHOR]

Abstract: Infrared light detection is generally limited by the intrinsic bandgap of semiconductors, which suppresses the freedom in infrared light photodetector design and hinders the development of high‐performance infrared light photodetector. In this work, for the first time infrared light (1030 nm) photodetectors are fabricated based on WS2/MoS2 heterostructures. Individual WS2 and MoS2 have no response to infrared light. The origin of infrared light response for WS2/MoS2 comes from the strong interlayer coupling which shrinks the energy interval in the heterojunction area thus rendering heterostructures longer wavelength detection ability compared to individual components. Considering the low light absorption due to indirect bandgap essence of few layers WS2/MoS2 heterostructures, its infrared responsivity is further enhanced with at most ≈25 times but the fast response rate is maintained via surface plasmon resonance (SPR). Such an interlayer coupling induced infrared light response and surface plasmon resonance enhancement strategy paves the way for high‐performance infrared light photodetection of infinite freedom in design. [ABSTRACT FROM AUTHOR]

Abstract: Actualizing highly efficient solution‐processed thermally activated delayed fluorescent (TADF) organic light‐emitting diodes (OLEDs) at high brightness becomes significant to the popularization of purely organic electroluminescence. Herein, a highly soluble emitter benzene‐1,3,5‐triyltris((4‐(9,9‐dimethylacridin‐10(9H)‐yl)phenyl)methanone was developed, yielding high delayed fluorescence rate (kTADF > 105 s−1) ascribed to the multitransition channels and tiny singlet–triplet splitting energy (ΔEST ≈ 32.7 meV). The triplet locally excited state is 0.38 eV above the lowest triplet charge‐transfer state, assuring a solely thermal equilibrium route for reverse intersystem crossing. Condensed state solvation effect unveils a hidden “trade‐off”: the reverse upconversion and triplet concentration quenching processes can be promoted but with a reduced radiative rate from the increased dopant concentration and the more polarized surroundings. Striking a delicate balance, corresponding vacuum‐evaporated and solution‐processed TADF‐OLEDs realized maximum external quantum efficiencies (EQEs) of ≈26% and ≈22% with extremely suppressed efficiency roll‐off. Notably, the wet‐processed one achieves to date the highest EQEs of 20.7%, 18.5%, 17.1%, and 13.6%, among its counterparts at the luminance of 1000, 3000, 5000, and 10 000 cd m−2, respectively. [ABSTRACT FROM AUTHOR]

Broadband photodetectors based on TiO2 nanotubes (NTs) array have significant prospects in many fields such as environmental monitoring. Herein, a simple spin-coating process is successfully adopted to incorporate MAPbI3 quantum dots (QDs) onto the surface of TiO2 NTs to form a heterostructure, extending the response range of TiO2 NT from ultraviolet to visible. Compared with pure TiO2 NTs, the heterostructure demonstrates an improvement of responsivity in visible range by three orders of magnitude, and maintains its response performance in the UV range simultaneously. The TiO2 NTs based heterostructure photodetectors demonstrate a relative fast and stable response in the 300-800 nm range and even have a reponsivity of 0.2 A W−1 at 700 nm. The photoelectric performance of the hybrid photodetector based on TiO2 NTs maintains well when exposed to moist air for 72 h or heated from room temperature to 100 °C. Moreover, such a TiO2 NTs/MAPbI3 QDs heterostructure device demonstrates excellent flexibility and high transparency (85%) in the 400-800 nm range, their photodetecting performance is well retained after 200 cycles of repeated bending at 90°. The present strategy that combines facile electrospinning and solution-processed QDs may open a new avenue for wide range response and flexible devices construction. [ABSTRACT FROM AUTHOR]

Due to the predicted excellent electronic properties superior to group VIB (Mo and W) transition metal dichalcogenides (TMDs), group IVB TMDs have enormous potential in nanoelectronics. Here, the synthesis of ultrathin HfS2 flakes via space-confined chemical vapor deposition, realized by an inner quartz tube, is demonstrated. Moreover, the effect of key growth parameters including the dimensions of confined space and deposition temperature on the growth behavior of products is systematically studied. Typical as-synthesized HfS2 is a hexagonal-like flake with a smallest thickness of ≈1.2 nm (bilayer) and an edge size of ≈5 µm. The photodetector based on as-synthesized HfS2 flakes demonstrates excellent optoelectronic performance with a fast photoresponse time (55 ms), which is attributed to the high-quality crystal structure obtained at a high deposition temperature and the ultraclean interface between HfS2 and the mica substrate. With such properties HfS2 holds great potential for optoelectronics applications. [ABSTRACT FROM AUTHOR]

β-In2S3 is a natural defective III--VI semiconductor attracting considerable interests but lack of efficient method for its 2D form fabrication. Here, for the first time, this paper reports controlled synthesis of ultrathin 2D β-In2S3 flakes via a facile space-confined chemical vapor deposition method. The natural defects in β-In2S3 crystals, clearly revealed by optical spectra and optoelectronic measurement, strongly modulate the (opto)-electronic of as-fabricated β-In2S3 and render it a broad detection range from visible to near-infrared. Particularly, the as-fabricated β-In2S3 photodetector shows a high photoresponsivity of 137 A W-1, a high external quantum efficiency of 3.78 x 104%, and a detectivity of 4.74 x 1010 Jones, accompanied with a fast rise and decay time of 6 and 8 ms, respectively. In addition, an interesting linear response to the testing power intensities range is observed, which can also be understood by the presence of natural defects. The unique defective structure and intrinsic optical properties of β-In2S3, together with its controllable growth, endow it with great potential for future applications in electronics and optoelectronics. [ABSTRACT FROM AUTHOR]

Multielemental systems enable the use of multiple degrees of freedom for control of physical properties by means of stoichiometric variation. This has attracted extremely high interest in the field of 2D optoelectronics in recent years. Here, for the first time, multilayer 2D ternary Ta2NiSe5 flakes are successfully fabricated using a mechanical exfoliation method from chemical vapor transport synthesized high quality bulk and the optoelectronic properties are systematically investigated. Importantly, a high responsivity of 17.21 A W−1 and high external quantum efficiency of 2645% are recorded from an as-fabricated photodetector at room temperature in air; this is superior to most other 2D materials-based photodetectors that have been reported. More intriguingly, a usual sublinear and an unusual superlinear light-intensity-dependent photocurrent are observed under air and vacuum, respectively. These excellent and special properties make multilayer ternary Ta2NiSe5 a highly competitive candidate for future infrared optoelectronic applications and an interesting platform for photophysics studies. [ABSTRACT FROM AUTHOR]

Rhenium disulfide (ReS2) is attracting more and more attention for its thickness-depended direct band gap. As a new appearing 2D transition metal dichalcogenide, the studies on synthesis method via chemical vapor deposition (CVD) is still rare. Here a systematically study on the CVD growth of continuous bilayer ReS2 film and single crystalline hexagonal ReS2 flake, as well as their corresponding optoelectronic properties is reported. Moreover, the growth mechanism has been proposed, accompanied with simulation study. High-performance photodetector based on ReS2 flake shows a high responsivity of 604 A·W−1, high external quantum efficiency of 1.50 × 105 %, and fast response time of 2 ms. ReS2 film-based photodetector exhibits weaker performance than the flake one; however, it still demonstrates a much faster response time (≈103 ms) than other reported CVD-grown ReS2-based photodetector (≈104-105 ms). Such good properties of ReS2 render it a promising future in 2D optoelectronics. [ABSTRACT FROM AUTHOR]

2D SnS2 nanosheets have been attracting intensive attention as one potential candidate for the modern electronic and/or optoelectronic fields. However, the controllable large-size growth of ultrathin SnS2 nanosheets still remains a great challenge and the photodetectors based on SnS2 nanosheets suffer from low responsivity, thus hindering their further applications so far. Herein, an improved chemical vapor deposition route is provided to synthesize large-size SnS2 nanosheets, the side length of which can surpass 150 μm. Then, ultrathin SnS2 nanosheet-based phototransistors are fabricated, which achieve high photoresponsivities up to 261 A W−1 (with a fast rising time of 20 ms and a falling time of 16 ms) in air and 722 A W−1 in vacuum, respectively. Furthermore, the effects of back-gate voltage and air adsorbates on the optoelectronic properties of the SnS2 nanosheet have been systematically investigated. In addition, a high-performance flexible photodetector based on SnS2 nanosheet is also fabricated with a high responsivity of 34.6 A W−1. [ABSTRACT FROM AUTHOR]

Solar-blind deep ultraviolet (DUV) photodetectors have been a hot topic in recent years because of their wide commercial and military applications. A wide bandgap (4.68 eV) of ternary oxide Zn2GeO4 makes it an ideal material for the solar-blind DUV detection. Unfortunately, the sensing performance of previously reported photodetectors based on Zn2GeO4 nanowires has been unsatisfactory for practical applications, because they suffer from long response and decay times, low responsivity, and quantum efficiency. Here, high-performance solar-blind DUV photodetectors are developed based on individual single-crystalline Zn2GeO4 nanowires. The transport mechanism is discussed in the frame of the small polaron theory. In situ electrical characterization of individual Zn2GeO4 nanowires reveals a high gain under high energy electron beam. The devices demonstrate outstanding solar-blind light sensing performances: a responsivity of 5.11 × 103 A W−1, external quantum efficiency of 2.45 × 106%, detectivity of ≈2.91 × 1011 Jones, τrise ≈ 10 ms, and τdecay ≈ 13 ms, which are superior to all reported Zn2GeO4 and other ternary oxide nanowire photodetectors. These results render the Zn2GeO4 nanowires particularly valuable for optoelectronic devices. [ABSTRACT FROM AUTHOR]

Fe-N-C Catalysts: Direct Growth of Carbon Nanotubes Doped with Single Atomic Fe-N4 Active Sites and Neighboring Graphitic Nitrogen for Efficient and Stable Oxygen Reduction Electrocatalysis (Adv. Funct. In article number 1906174, Jia Li, Lin Gan, Feiyu Kang, and co-workers report the direct growth of carbon nanotubes doped with Fe-N SB 4 sb moieties for improved electrocatalytic stability in the cathodic oxygen reduction reaction (ORR) in proton-exchange-membrane fuel cells. By increasing the neighboring graphitic nitrogen, the Fe-N SB 4 sb moieties also show enhanced activity due to the modified spin state of the Fe center and thereby optimized binding energy with ORR intermediates. [Extracted from the article]

Two dimensional (2D) magnetic materials display enormous application potential in spintronic fields. However, most of currently reported magnetic materials are van der Waals layered structure that is easy to be isolated via exfoliation method. By contrast, the studies on non‐van der Waals ultrathin magnetic materials are rare, largely due to the difficulty in fabrication. Rhombohedral Cr2S3, an intensively studied antiferromagnetic transition metal chalcogenide with Neel temperature of ≈120 K, has a typical non‐van der Waals structure. Restricted by the strong covalent bonding in all the three dimensions of non‐van der Waals structure, the synthesis of ultrathin Cr2S3 single crystals is still a challenge that is not achieved yet. Besides, the study on the Raman modes of rhombohedral Cr2S3 is also absent. Herein, by employing space‐confined chemical vapor deposition strategy, ultrathin rhombohedral Cr2S3 single crystals with a thickness down to ≈2.5 nm for the first time are successfully grown. Moreover, a systematically investigation is also conducted on the Raman vibrations of ultrathin rhombohedral Cr2S3. With the aid of angle‐resolved polarized Raman technique, the Raman modes of rhombohedral Cr2S3 for the first time based on crystal symmetry and Raman selection rules are rationally assigned. By combining space‐confined chemical vapor deposition and van der Waals substrate, ultrathin Cr2S3 single crystals with a thickness of 2.5 nm are synthesized for the first time. With the aid of the angle‐resolved polarized Raman technique, the Raman modes of rhombohedral Cr2S3 are rationally assigned based on crystal symmetry and Raman selection rules. [ABSTRACT FROM AUTHOR]

Inversion symmetry broken 3R phase semiconducting transition metal dichalcogenides (TMDC) have huge potential applications in many novel fields, such as valleytronics and nonlinear optics for the strong spin–orbit coupling and particularly the persistent noncentrosymmetric structure regardless the layer numbers, in stark contrast to the strict layer number requirement in other phases. Unfortunately, the fabrication of 3R phase TMDC is still a huge task to date. Molybdenum telluride (MoTe2) attracts increasing interest in recent years due to the easy transition between its various phases and its narrow bandgap close to silicon. However, the weak Mo–Te bond and the small energy imparity among phases make it a big challenge to obtain pure‐phase single crystalline MoTe2, especially; it is still a virgin land to obtain two‐dimensional (2D) 3R‐MoTe2. Here, by rational controlling the deposition temperature and tellurization velocity, for the first time high quality 2D 3R‐MoTe2 flakes are synthesized via chemical vapor deposition from a MoCl5 precursor. Scanning transmission electron microscopy unambiguously reveals the 3R stacking mode of as‐synthesized MoTe2. Second harmonic generation measurement confirms the excellent odd/even layer‐independent frequency conversion efficiency. Besides, the outstanding intrinsic infrared detection ability of as‐synthesized 3R‐MoTe2 is demonstrated as well. Inversion symmetry broken 2D 3R‐MoTe2 single crystals are synthesized by chemical vapor deposition for the first time. Such a novel noncentrosymmetric structure renders it with high frequency conversion efficiency in second harmonic generation and strong spin–orbit coupling, suggesting its promising future in the applications of nonlinear optics and valleytronics. [ABSTRACT FROM AUTHOR]

On page 704, T. Y. Zhai and co‐workers prepare high‐performance solar‐blind DUV photodetectors based on individual CVD‐fabricated Zn2GeO4 nanowire and perform in‐depth analysis of their optoelectronic characteristics. The device demonstrates outstanding solar‐blind light sensing performance with a high responsivity, a high external quantum efficiency, and a fast response speed. [ABSTRACT FROM AUTHOR]

Abstract: Inversion symmetry broken 3R phase semiconducting transition metal dichalcogenides (TMDC) have huge potential applications in many novel fields, such as valleytronics and nonlinear optics for the strong spin–orbit coupling and particularly the persistent noncentrosymmetric structure regardless the layer numbers, in stark contrast to the strict layer number requirement in other phases. Unfortunately, the fabrication of 3R phase TMDC is still a huge task to date. Molybdenum telluride (MoTe2) attracts increasing interest in recent years due to the easy transition between its various phases and its narrow bandgap close to silicon. However, the weak Mo–Te bond and the small energy imparity among phases make it a big challenge to obtain pure‐phase single crystalline MoTe2, especially; it is still a virgin land to obtain two‐dimensional (2D) 3R‐MoTe2. Here, by rational controlling the deposition temperature and tellurization velocity, for the first time high quality 2D 3R‐MoTe2 flakes are synthesized via chemical vapor deposition from a MoCl5 precursor. Scanning transmission electron microscopy unambiguously reveals the 3R stacking mode of as‐synthesized MoTe2. Second harmonic generation measurement confirms the excellent odd/even layer‐independent frequency conversion efficiency. Besides, the outstanding intrinsic infrared detection ability of as‐synthesized 3R‐MoTe2 is demonstrated as well. [ABSTRACT FROM AUTHOR]

Inversion symmetry broken 3R phase semiconducting transition metal dichalcogenides (TMDC) have huge potential applications in many novel fields, such as valleytronics and nonlinear optics for the strong spin–orbit coupling and particularly the persistent noncentrosymmetric structure regardless the layer numbers, in stark contrast to the strict layer number requirement in other phases. Unfortunately, the fabrication of 3R phase TMDC is still a huge task to date. Molybdenum telluride (MoTe2) attracts increasing interest in recent years due to the easy transition between its various phases and its narrow bandgap close to silicon. However, the weak Mo–Te bond and the small energy imparity among phases make it a big challenge to obtain pure‐phase single crystalline MoTe2, especially; it is still a virgin land to obtain two‐dimensional (2D) 3R‐MoTe2. Here, by rational controlling the deposition temperature and tellurization velocity, for the first time high quality 2D 3R‐MoTe2 flakes are synthesized via chemical vapor deposition from a MoCl5 precursor. Scanning transmission electron microscopy unambiguously reveals the 3R stacking mode of as‐synthesized MoTe2. Second harmonic generation measurement confirms the excellent odd/even layer‐independent frequency conversion efficiency. Besides, the outstanding intrinsic infrared detection ability of as‐synthesized 3R‐MoTe2 is demonstrated as well. Inversion symmetry broken 2D 3R‐MoTe2 single crystals are synthesized by chemical vapor deposition for the first time. Such a novel noncentrosymmetric structure renders it with high frequency conversion efficiency in second harmonic generation and strong spin–orbit coupling, suggesting its promising future in the applications of nonlinear optics and valleytronics. [ABSTRACT FROM AUTHOR]