Surface-Stress-Induced Phase Transformation of Ultrathin FeCo Nanowires

Ultrathin metal nanowires have attracted wide attention becau se oftheir unique anisotropy and surface-to-volume effects. In this study, we use ultrathin Au nanowires as the templating core to epitaxially grow magnetic iron–cobalt (FeCo) shell through metal-redox with the control on their thickness and stoichiometry. Large surface-stress-induced phase transformation in Au nanowires triggers and stabilizes metastable tetragonal FeCo nanostructure to enhance its magnetic anisotropy and coercivity. Meanwhile, under illumination, plasmon-induced hotspot in ultrathin Au nanowires enables the light-control on magnetic characteristics of FeCo shell. This study demonstrates the feasibility of surface-stress-induced phase transformation to stabilize and control metastable nanostructures for enhanced magnetic anisotropy, which is one of the key properties of functional magnetic materials

Ligand-Passivated Eu:Y₂O₃ Nanocrystals as a Phosphor for White Light Emitting Diodes

Eu(III)-doped Y2O3 nanocrystals are prepared by microwave synthetic methods as spherical 6.4 ± 1.5 nm nanocrystals with a cubic crystal structure. The surface of the nanocrystal is passivated by acetylacetonate (acac) and HDA on the Y exposed facet of the nanocrystal. The presence of acac on the nanocrystal surface gives rise to a strong S0 → S1 (π → π*, acac) and acac → Ln3+ ligand to metal charge transfer (LMCT) transitions at 270 and 370 nm, respectively, in the Eu:Y2O3 nanocrystal. Excitation into the S0 → S1 (π → π*) or acac → Ln3+ LMCT transition leads to the production of white light emission arising from efficient intramolecular energy transfer to the Y2O3 oxygen vacancies and the Eu(III) Judd–Ofelt f–f transitions. The acac passivant is thermally stable below 400 °C, and its presence is evidenced by UV–vis absorption, FT-IR, and NMR measurements. The presence of the low-lying acac levels allows UV LED pumping of the solid phosphor, leading to high quantum efficiency (∼19%) when pumped at 370 nm, high-quality white light color rendering (CIE coordinates 0.33 and 0.35), a high scotopic-to-photopic ratio (S/P = 2.21), and thermal stability. In a LED lighting package luminosities of 100 lm W–1 were obtained, which are competitive with current commercial lighting technology. The use of the passivant to funnel energy to the lanthanide emitter via a molecular antenna effect represents a new paradigm for designing phosphors for LED-pumped white light

Pulsed Laser Deposition of CdSe Quantum Dots on Zn₂SnO₄ Nanowires and Their Photovoltaic Applications

In this work we report a physical deposition-based, one-step quantum dot (QD) synthesis and assembly on ternary metal oxide nanowires for photovoltaic applications. Typical solution-based synthesis of colloidal QDs for QD sensitized solar cells involves nontrivial ligand exchange processing and toxic wet chemicals, and the effect of the ligands on carrier transport has not been fully understood. In this research using pulsed laser deposition, CdSe QDs were coated on Zn₂SnO₄ nanowires without ligand molecules, and the coverage could be controlled by adjusting the laser fluence. Growth of QDs in dense nanowire network structures was also achieved, and photovoltaic cells fabricated using this method exhibited promising device performance. This approach could be further applied for the assembly of QDs where ligand exchange is difficult and could possibly lead to reduced fabrication cost and improved device performance

Interface Passivation of Inverted Perovskite Solar Cells by Dye Molecules

The interface between [6,6]-phenyl C61-butyric acid methyl ester (PC61BM) and the electrode has a critical effect on the performance of inverted perovskite solar cells (PSCs). Three organic cationic cyanine dye molecules with different highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) states are designed to passivate the PC61BM and Ag electrode interface to improve PSCs performance. The effects of energy-level alignment and the interfacial charge transfer resistance on the device performance are compared and studied. The dye interface passivation layer significantly reduces charge recombination. Moreover, the ClO4– anions associated with the dye molecules improve the charge extraction and charge transport in the devices. Reduced interface charge recombination and improved charge transport are confirmed by photoluminescence (PL), time-resolved photoluminescence (TRPL), electrochemical impedance spectra (EIS), and charge-only device performance studies. The PSCs with one of the dyes as an interface passivation layer show an optimized power conversion efficiency (PCE) of 19.14% with an open-circuit voltage (Voc) of 1.09 V, a short-circuit current density (Jsc) of 22.87 mA/cm2, and a fill factor (FF) of 76.81%. The devices maintain over 90% of the initial PCE for 120 h of storage under an ambient environment (25 °C and 30 ± 5% relative humidity (RH). The use of small dye molecules as an interface passivation layer to reduce charge recombination in PSCs represents a paradigm for improving the performance and stability of PSCs

Enhanced Perovskite Solar Cell Performance via 2‑Amino-5-iodobenzoic Acid Passivation

The intrinsic stability issues of the perovskite materials threaten the efficiency and stability of the devices, and stability has become the main obstacle to industrial applications. Herein, the efficient and facile passivation strategy by 2-amino-5-iodobenzoic acid (AIBA) is proposed. The impact of AIBA on the properties of the perovskite films and device performance is systemically studied. The results show that the trap states are eliminated without affecting the crystal properties of the perovskite grains, leading to the enhanced performance and stability of the perovskite solar cells (PSCs). A high power conversion efficiency (PCE) of 20.23% and lower hysteresis index (HI) of 1.49‰ are achieved, which represent one of the most excellent PCE and HI values for the inverted PSCs based on MAPbI3/[6,6]-Phenyl-C61-Butyric Acid Methyl Ester (PCBM) planar heterojunction structure. Moreover, the UV stability of the perovskite films and the thermal and moisture stability of the devices are also enhanced by the AIBA passivation. The PCE of the device with AIBA can maintain about 83.41% for 600 h (40 RH %) and 64.06% for 100 h (55–70 RH %) of its initial PCE value without any encapsulation, while the control device can maintain only about 72.91 and 45.59% of its initial PCE. Density functional theory calculations are performed to study the origins of enhanced performance. Interestingly, the results show that the surface states induced by AIBA can facilitate the photoexcited charge transfer dynamics and reduce the electron–hole recombination loss. The passivation method developed in this work provides an efficient way to enhance the stability and performance of inverted PSCs

Synthesis of Graphene Oxide Based CuO Nanoparticles Composite Electrode for Highly Enhanced Nonenzymatic Glucose Detection

CuO nanoparticles (NPs) based graphene oxide (CuO/GO) composites with different CuO NPs loading amount as well as pure CuO NPs with different hydrothermal temperatures were synthesized using a hydrothermal method. Transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and Raman spectroscopy were employed to characterize the morphology and structures of our samples. The influence of hydrothermal temperature, GO sheet, and loading amount of CuO on particle size and structure of CuO was systemically investigated. The nonenzymatic biosensing properties of CuO/GO composites and CuO NPs toward glucose were studied based on glassy carbon electrode (GCE). The sensing properties of CuO NPs were improved after loading on GO sheets. The CuO/GO composites with saturated loading of the CuO NPs exhibited the best nonenzymatic biosensing behavior. It exhibited a sensitivity of 262.52 μA mM^–1 cm^–2 to glucose with a 0.69 μM detection limit (<i>S</i>/<i>N</i> = 3) and a linear range from 2.79 μM to 2.03 mM under a working potential of +0.7 V. It also showed outstanding long term stability, good reproducibility, excellent selectivity, and accurate measurement in real serum sample. It is believed that CuO/GO composites show good promise for further application on nonenzymatic glucose biosensors

High-Performance CsPbIBr₂ Perovskite Solar Cells: Effectively Promoted Crystal Growth by Antisolvent and Organic Ion Strategies

Growing attention has been paid to CsPbIBr2 perovskite solar cells (PSCs) after balancing the band gap and stability features of the interested full-inorganic perovskites. However, their power-conversion efficiency (PCE) still lags behind that of the PSCs using hybrid halide perovskite and how to increase the corresponding PCE is still a challenge. Herein, antisolvents and organic ion surface passivation strategies were systematically applied to precisely control the growth of CsPbIBr2 crystals for constructing a high-quality full-inorganic perovskite film. Through careful adjustments, a CsPbIBr2 film with a pure phase, full coverage, and high crystallinity with preferable (100) orientation was successfully obtained by introducing diethyl ether as the antisolvent followed by guanidinium surface passivation. The optimal CsPbIBr2 film was composed by a large grain with an average size of 950 nm, few grain boundaries, and higher hydrophobic property. Planer PSC using the optimal CsPbIBr2 film and electron-beam-deposited TiO2 compact layer exhibits a PCE of 9.17%, which ranks among the highest PCE range of the reported CsPbIBr2 PSCs. Besides, the designed CsPbIBr2 PSC exhibited good long-term stability, which could maintain 90% of the initial PCE in 40% humidity ambient, which remained constant after heat treatment at 100 °C for 100 h. Based on the optimal CsPbIBr2 film, the flexible and large-area (up to 225 mm2) PSCs were further fabricated. The adopted film improvement methods were further extended to other kinds of full-organic PSCs, which demonstrated the universality of this strategy

Transcriptome analysis reveals molecular regulation mechanism of Tibet sheep tolerance to high altitude oxygen environment

As one of the most important livestock breeds on the Qinghai-Tibet Plateau, Tibetan sheep are of great importance to the local economy, agriculture and culture. Its adaptive mechanism in low temperature and low oxygen at highland altitudes has not been reported. In this study, transcriptome sequencing was used to analyze the heart, liver, spleen, lung, kidney, and muscle tissue of sheep at low and highland altitudes. LOC101112291, SELENOW, COL3A1, GPX1, TMSB4X and HSF4 were selected as candidate genes for adapting to plateau characteristics in Tibet Sheep. Besides, glutathione metabolism, arachidonic acid metabolism, nucleotide excision repair, regulation of actin cytoskeleton, protein digestion and absorption, thyroid hormone synthesis, relaxation signaling pathways may play important roles in the adaptation to plateau hypoxia, and cold tolerance. Structural analysis also showed that sequencing genes related to the adaptation mechanism of Tibet sheep to highland altitude. This study will lay a certain foundation for Tibet sheep research. Tibet sheep are an ancient species in the Qinghai Tibet Plateau. After a long period of domestication. Tibet sheep adapt to the hypoxic environment of the plateau in terms of physiology and morphology. At the same time, Tibet sheep is also one of the major sources of material for herdsmen in tibetan. In this study, six different tissue samples (heart, liver, spleen, lung, kidney, and muscle) of Tibet sheep were analyzed to reveal the underlying mechanisms of different tissues respond to hypothermia condition. The results showed that six key genes and eight important signaling pathways involved in regulating the adaptation of Tibet sheep to the plateau. In addition, there were more alternative splicing (AS) events and single nucleotide polymorphism (SNP) sites in highland altitude Tibet sheep than in lowland altitude sheep, which was also a concern in the highland altitude adaptability of Tibet sheep.</p

Yb₂O₃/Au Upconversion Nanocomposites with Broad-Band Excitation for Solar Cells

Luminescent upconversion (UC) is a promising way to harvest near-infrared (NIR) sunlight and improve the power conversion efficiency (PCE) of solar cells. However, most of efficient upconversion phosphors (UCPs) are based on 4f–4f transitions of rare earth (RE) ions, which have only a narrower excitation band matching with sun spectrum. To solve this significant problem, we designed and fabricated a novel kind of efficient UC nanocomposites, Yb2O3/Au, in which the upconversion luminescence (UCL) of Yb2O3 was a white broad band that originated from electron–hole recombination, and the excitation bands were expanded at least a range of 770–980 nm through the energy transfer (ET) from anisotropic gold nanoparticles (GNPs) to the Yb2O3 host. To our knowledge, the direct ET from the noble metal to the lanthanide phosphors has never been evidenced. Exploring Yb2O3/Au as the upconverter of a dye-sensitized solar cell (DSSC), NIR photovoltaic response was successfully demonstrated as proof-of-concept

Perovskite Films Treated with Polyvinyl Pyrrolidone for High-Performance Inverted Perovskite Solar Cells

Energy loss and unstable properties of the interface and grain boundaries (GBs) in perovskite solar cells (PSCs) greatly limit the efficiency and stability of PSCs. Here, a polyvinyl pyrrolidone (PVP) treatment is proposed to overcome these challenges. The impact of PVP treatment on perovskite films and the corresponding performance of the devices are systemically investigated. The crystallinity, GBs, and PbI2 residues of the perovskite films are all improved via the interaction of PVP and perovskite crystals, which results in an increased grain size and enhanced built-in electric field in the devices. The trap density is dramatically decreased from 8.74 × 1015 to 4.37 × 1015 cm–3, and the additional interface electrical field of 1.26 × 106 V/cm is formed at the perovskite/PCBM interface, which dramatically eliminates the energy loss of the bulk and interface of inverted PSCs. Based on this strategy, a high power conversion efficiency (PCE) of 20.77% is achieved based on the MAPbI3/PCBM planar heterojunction. In addition, the stability of PSCs is also dramatically improved, and the PCE of PVP devices can retain 80% of its initial value after 14 days in air and can retain 99% of its initial value after 64 days in N2, while the control devices can only retain 44 and 85% of their initial PCE values under the same exposure conditions, respectively