"Nature" and "Science" Week (4.10-4.16) Frontiers of Materials Science

1.La-doped BaSnO3 (LBSO) perovskite solar cells (Colloidally prepared La-doped BaSnO3electrodes for efficient, photostable perovskite solar cells)
There have been many reports of more than 20% energy conversion efficiency (PCE) of perovskite solar cells (PSCs) using mesoporous TiO2 as an electron transport layer. However, TiO2 can reduce the stability of PSCs during illumination, including ultraviolet light. The electron transport and electronic structure of La-doped BaSnO3 (LBSO) perovskite make it an ideal alternative material, but well-dispersed fine-grained LBSO or LBSO with a good synthesis temperature below 500 °C achieve. Shin et al. prepared a LBSO electrode using a superoxide sol solution method under mild conditions below 300 °C. PSCs prepared using LBSO and methylamine lead iodide (MAPbI3) exhibited a stable PCE of 21.2%. This PSCs retained 93% of the initial performance after 1000 hours of full sunlight. (Science DOI: 10.1126/science.aam6620)
2. Ultra-strong lattice communication and high-density nanoprecipitation to achieve ultra-strength steel (Ultrastrong steelvia minimal lattice misfit and high-density nanoprecipitation) Lightweight design strategies and advanced energy applications are urgently needed for the next generation of high performance structural materials. Maraging steel, a martensite that combines nanoprecipitates, is a high-strength material that has the potential to meet the above requirements and become the next generation of high-performance structural materials. Jiang et al. reported a new “intuitive” design strategy for the synthesis of super-strong steel alloys using high-density nanoprecipitation with minimal lattice mismatch. They found that these highly dispersed, fully coherent precipitates (that is, the crystal lattice of the precipitate is almost identical to the crystal lattice of the surrounding parent) exhibit very low lattice mismatch (0.03 ± 0.04%) and a high inverse The phase grain boundary energy strengthens the alloy without sacrificing ductility. Such low lattice mismatch reduces the nucleation energy barrier of the precipitate, thus making the nanoprecipitate extremely high in number density (10e24/m3) and small in size (2.7±0.2 nm). They synthesized a series of Ni (Al, Fe) reinforced such super-strength steels with a strength of 2.2 GPa and a ductility of about 8.2%. Compared to conventional maraging steels, these precipitate components (Ni, Al, Fe) greatly reduce the cost by replacing the original expensive Co and Ti. (Nature DOI: 10.1038/nature22032)
3. Transition metal-catalyzed alkyl-alkyl bond formation: Another dimension in cross-coupling chemistry Since the backbone of most organic molecules is composed of basic CC bonds, developing effective methods to construct these bonds has become one of the important challenges that organic synthesis must face. The transition metal catalyzes the cross-linking reaction between the organic electrophile and the nucleophile is a very powerful tool for achieving CC bond formation. Recently, a large number of cross-linking coupling processes have used aryl or alkenyl electrophiles as one of the coupling bodies. Over the past 15 years, scientists have developed various new methods for efficient cross-linking of many alkyl electrophiles, thus greatly expanding the diversity of target molecules. The ability to couple alkyl electrophiles opens the door to the three-dimensional chemical dimension, significantly increasing the application of the cross-linking coupling process. (Science DOI: 10.1126/science.aaf7230)
4. Synthesis of carbon nanobelts (Synthesis of acarbon nanobelt) The carbon nanobelt is composed of a closed loop of a fully-fused co-boundary benzene ring, which is a target that has plagued the organic chemistry community for more than 60 years. Recently, Povie et al. synthesized this carbon nanobelt by iterative Wittig reaction and subsequent Ni-modulation aryl-aryl coupling reaction. X-ray diffraction confirmed this cylindrical band structure, and its basic photoelectric properties were further studied by ultraviolet-visible absorption, fluorescence and Raman spectroscopy, and theoretical calculations. This molecule can be used as a seed for the synthesis of well-structured carbon nanotubes (Science DOI:10.1126/science.aam8158)
5. Observing the frozen charge of a Kondo resonance The ability to control electronic states at the nanoscale is important for understanding condensed matter. In particular, quantum dot circuits represent a model system for studying strong electron correlation and are a microcosm of the Kondo effect. Desjardins et al. studied the intrinsic degree of freedom of this multibody phenomenon using a circuit quantum electrodynamic architecture. They couple a quantum dot into a high-quality microwave cavity and measure the electronic compression of the quantum dot, which is the ability to hold electrons. They directly reveal the charge dynamics of the electron transfer mechanism through dual conductance and compression measurements in the Kondo region. They found that Kondo resonances visible in transmission measurements are "transparent" for capturing microwave photons in high-quality cavities, thus revealing that in a multi-body resonance, limited conduction can be frozen by Coulomb interactions. to fulfill. (Nature DOI: 10.1038/nature21704)
6. High performance light emitting diodes (LEDs)
(High-performance light-emitting diodes based on carbene-metal-amides) Organic LEDs are a highly efficient illumination and display technology. Di et al. reported a new linear donor-bridge-acceptor luminescent molecule that is easy to handle and achieves nearly 100% internal quantum efficiency at high brightness. The key to this performance is the fast and efficient use of triplet states. They used time-resolved spectroscopy to determine that fluorescence through the triplet at room temperature can occur within 350 ns. They found that the geometry of the molecule exists in a singlet-triplet energy gap (exchange energy) close to zero, so that rapid interconversion is possible. Theoretical calculations show that the exchange energy can be adjusted by the relative rotation of the bridged donor and acceptor. Unlike other low-energy systems, the basic oscillator strength is maintained at the singlet-triplet degeneracy point. (Science DOI: 10.1126/science.aah4345)
7. Position-dependent and millimetre-range photodetection in phototransistors with micrometre-scale graphene on SiC The excellent optoelectronic properties of graphene make it an important part of high performance photodetectors. However, in a typical graphene-based photodetector, the photoresponse is only from a specific location near the graphene, which is very small compared to the device size. For many optoelectronic device applications, it is desirable to achieve a large area of ​​light response and position sensitivity. Sarker et al. studied the spatial response of light response in a back-gate graphene field effect transistor (GFET) on a SiC substrate by scanning a focused laser beam. GFETs exhibit a non-local photoresponse, even when irradiated onto a SiC substrate 500 microns from graphene. Different illumination positions can cause photo response characteristics and photocurrent changes to exceed an order of magnitude. (Nature Nanotechnology DOI: 10.1038/NNANO.2017.46)
8. Intrinsic non -radiative voltage losses in fullerene-based organic solar cells The external quantum efficiency and fill factor exhibited by organic solar cells have approached traditional photovoltaic technology. However, the open circuit voltage is very low due to the occurrence of important non-radiative re-growth compared to the optical band gap of the absorbing material. Benduhn et al. studied data from many published data and new materials and found that the non-radiative voltage loss decreases as the energy of the transferred charge state increases. With the charge transfer in the Marcus inversion region, the decay of the non-radiative charge transfer state explains this phenomenon. Their results indicate an intrinsic link between non-radiative voltage loss and electronic vibration coupling, indicating that such losses are inevitable. Therefore, the theoretical upper limit of the energy conversion efficiency of a single junction organic solar cell may be reduced to 25.5%, and the optimal optical band gap is increased to 1.45-1.65 eV, which is 0.2-0.3 eV higher than the value of the minimum non-radiative voltage loss technique. (Nature Energy DOI: 10.1038/nenergy.2017.53)

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