Bi2 Te3 /Bi2 Se3 /Bi2 S3 Cascade Heterostructure for Fast-Response and High-Photoresponsivity Photodetector and High-Efficiency Water Splitting with a Small Bias Voltage.

Large-scale multi-heterostructure and optimal band alignment are significantly challenging but vital for photoelectrochemical (PEC)-type photodetector and water splitting. Herein, the centimeter-scale bismuth chalcogenides-based cascade heterostructure is successfully synthesized by a sequential vapor phase deposition method. The multi-staggered band alignment of Bi2 Te3 /Bi2 Se3 /Bi2 S3 is optimized and verified by X-ray photoelectron spectroscopy. The PEC photodetectors based on these cascade heterostructures demonstrate the highest photoresponsivity (103 mA W-1 at -0.1 V and 3.5 mAW-1 at 0 V under 475 nm light excitation) among the previous reports based on two-dimensional materials and related heterostructures. Furthermore, the photodetectors display a fast response (≈8 ms), a high detectivity (8.96 × 109 Jones), a high external quantum efficiency (26.17%), and a high incident photon-to-current efficiency (27.04%) at 475 nm. Due to the rapid charge transport and efficient light absorption, the Bi2 Te3 /Bi2 Se3 /Bi2 S3 cascade heterostructure demonstrates a highly efficient hydrogen production rate (≈0.416 mmol cm-2  h-1 and ≈14.320 µmol cm-2  h-1 with or without sacrificial agent, respectively), which is far superior to those of pure bismuth chalcogenides and its type-II heterostructures. The large-scale cascade heterostructure offers an innovative method to improve the performance of optoelectronic devices in the future.

Vertically oriented SnS2 on MoS2 nanosheets for high-photoresponsivity and fast-response self-powered photoelectrochemical photodetectors.

Van der Waals heterostructures have great potential for the emerging self-powered photoelectrochemical photodetectors due to their outstanding photoelectric conversion capability and efficient interfacial carrier transportation. By considering the band alignment, structural design, and growth optimization, the heterostructures of vertically oriented SnS2 with different densities on MoS2 nanosheets are designed and fabricated using a two-step epitaxial growth method. Compared with SnS2, MoS2, and low density-vertical SnS2/MoS2 heterostructure, the high density-vertical SnS2/MoS2 heterostructure exhibits largely enhanced self-powered photodetection performances, such as a giant photocurrent density (∼932.8 µA cm-2), an excellent photoresponsivity (4.66 mA W-1), and an ultrafast response/recovery time (3.6/6.4 ms) in the ultraviolet-visible range. This impressive enhancement of high density-vertical SnS2/MoS2 photodetectors is mainly ascribed to the essentially improved charge transfer and carrier transport of type-II band alignment heterostructures and the efficient light absorption from the unique light-trapping structure. In addition, the photoelectrocatalytic water splitting performance of the high density-vertical SnS2/MoS2 heterostructure also benefits from the type-II band alignment and the light-trapping structure. This work provides valuable inspiration for the design of two-dimensional optoelectronic and photoelectrochemical devices with improved performance by the morphology and heterostructure design.

Sb2S3/Sb2Se3 heterojunction for high-performance photodetection and hydrogen production.

Photoelectrochemical (PEC)-type devices provide promising ways for harvesting solar energy and converting it to electric and chemical energy with a low-cost and simple manufacturing process. However, the high light absorption, fast carrier separation, and low carrier recombination are still great challenges in reaching high performance for PEC devices. As emergent two-dimensional (2D) materials, Sb2Se3 and Sb2S3 exhibit desirable photoelectric properties due to the narrow bandgap, large optical absorption, and high carrier mobility. Herein, Sb2S3/Sb2Se3 heterojunction is synthesized by a two-step physical vapor deposition method. The type-II Sb2S3/Sb2Se3 heterojunction displays excellentphotoelectric properties such as a high photocurrent density (Iph âˆ¼ 162 µA cm-2), a high photoresponsivity (Rph âˆ¼ 3700 µA W-1), and a fast time response speed (rising time ∼ 2 ms and falling time ∼ 4.5 ms) even in harsh environment (H2SO4 electrolyte). Especially, the Sb2S3/Sb2Se3 shows an excellent self-powered photoresponse (Iph âˆ¼ 40 µA cm-2, Rph âˆ¼ 850 µA W-1). This increment is attributed to the improvement in light absorption, charge separation, and charge transfer efficiency. Taking these advantages, the Sb2S3/Sb2Se3 heterojunction also exhibits higher PEC water splitting synergically, which is approximately 3 times larger than that of Sb2Se3 and Sb2S3. These results pave the way for high-performance PEC devices by integrating 2D narrow bandgap semiconductors.

Enhanced UV-Vis photodetector performance by optimizing interfacial charge transportation in the heterostructure by SnS and SnSe2.

Optimizing interfacial charge transfer in type-II heterostructures, is one promising solution to improve efficiency of the solar energy conversion in photodetectors and solar cells. Herein, the SnS/SnSe2/ITO and SnSe2/SnS/ITO heterostructures are prepared by two-step physical vapor epitaxial growth. X-ray photoelectron spectroscopy confirms the SnS/SnSe2 heterostructure belongs to type-II band-alignment. The SnS/SnSe2 based photodetector shows higher photoresponsivity, which is approximately 2, 9, and 14 times larger than that of SnSe2/SnS, SnSe2, and SnS, respectively. The improvement of SnS/SnSe2 in photoelectric response mainly comes from high light harvesting and efficient charge transportation than individual SnSe2 and SnS, which is verified by UV-Vis absorption spectra. Electrochemical impedance spectroscopy, open circuit potentials, and Mott-Schottky characterization results further confirm that the better photodetection performance of SnS/SnSe2/ITO than that of SnSe2/SnS/ITO heterostructure is from the appropriate energy level cascade facilitating electron transport. These results provide an effective way to further improve the performance of heterostructure-based optoelectronic devices by an appropriate interface design.

Layer-Dependent Nonlinear Optical Properties of WS2, MoS2, and Bi2S3 Films Synthesized by Chemical Vapor Deposition.

Two-dimensional (2D) layered materials have shown layer-dependent optical properties in both linear optical and nonlinear optical (NLO) regimes due to prominent interlayer coupling and quantum confinement in an atomic scale. However, the NLO properties become more complicated as both saturable absorption (SA) and reverse saturable absorption (RSA) easily happen in 2D materials, which results in a significant challenge to understand the evolution of nonlinear absorption with layers. Motivated by this, chemical vapor-deposited chalcogenide compounds (WS2, MoS2, and Bi2S3) are used to investigate the pump intensity and layer number-dependent NLO properties. The values of nonlinear absorption coefficients of these chalcogenide compounds increase with the pump intensity by an 800 nm femtosecond laser, which can be described by an empirical power law function. The SA process due to the large transition probability of the ground state readily takes place in thick samples, while RSA occurs easily in thin samples due to the two-photon absorption (TPA). The transition from TPA to SA is deduced to occur at 13L-WS2, 15L-MoS2, and 5L-Bi2S3, which is related to the layer-dependent band gaps. Our results provide an efficient way to tune optical nonlinearities with a controlled layer number and to design corresponding NLO devices such as optical switches and saturable absorbers.

Soluble CD83 inhibits acute rejection by up regulating TGF-ß and IDO secretion in rat liver transplantation.

BACKGROUND: Allogeneic transplantation immune tolerance is currently a hot research issue and soluble CD83(sCD83) is a novel immunomodulator with great potential in inducing transplantation tolerance. OBJECTIVE: To investigate the mechanism of the immune tolerance effect of sCD83 on rat liver transplantation. METHOD: A rat liver transplantation model was established to study the effects of sCD83 on the expression levels of IL-2, IL-10, and TGF-ß in peripheral blood and the mRNA expressions of foxp3, TGF-ß, and Indoleamine 2,3-dioxygenase (IDO) in liver. The expression changes of costimulatory molecules CD80, CD86, and MHC-II on the surface of DC cells and the expressions of IDO + DC cell, TGF-ß + CD4 + T cell, and CD4 + CD25 + Foxp3 + T cell were analyzed and compared. RESULTS: sCD83 alleviated the rejection activity index (RAI) of rat liver transplantation in the early stage, increased the expressions of TGF-ß, IL-10 in peripheral blood and the mRNAs of IDO, TGF-ß and foxp3 in the transplanted liver, and down-regulated the expressions of MHC-II, CD86, and CD80 in DC cells, resulting in significant increased numbers of tolerogenic TGF-ß + CD4 + T cells, Treg cells, and IDO + DC cells with low expression. CONCLUSION: sCD83 inhibited acute rejection after liver transplantation in an allogeneic rat, and the mechanism was associated with the effect that sCD83 increased the expression of TGF-ß, activated IDO immunosuppressive pathway, and increased tolerogenic DC cells and Treg cells.