Methylammonium lead iodide perovskite has attracted considerable recent interest for solution processable solar cells and other optoelectronic applications. The orthorhombic-to-tetragonal phase ...transition in perovskite can significantly alter its optical, electrical properties and impact the corresponding applications. Here, we report a systematic investigation of the size-dependent orthorhombic-to-tetragonal phase transition using a combined temperature-dependent optical, electrical transport and transmission electron microscopy study. Our studies of individual perovskite microplates with variable thicknesses demonstrate that the phase transition temperature decreases with reducing microplate thickness. The sudden decrease of mobility around phase transition temperature and the presence of hysteresis loops in the temperature-dependent mobility confirm that the orthorhombic-to-tetragonal phase transition is a first-order phase transition. Our findings offer significant fundamental insight on the temperature- and size-dependent structural, optical and charge transport properties of perovskite materials, and can greatly impact future exploration of novel electronic and optoelectronic devices from these materials.
A series of twisted D–π–A type emitters based on the acridine donor unit and CN‐substituted pyridine, pyrimidine, and benzene acceptor units are studied. They not only allow one to systematically ...probe the influence of different acceptor strengths, but also permit one to intriguingly probe the influence of tunable conformations (twist angles) within the acceptor moieties through controlling the orientation of asymmetric heteroaromatic ring relative to the donor component. Intramolecular charge‐transfer transitions are observed in all these compounds and emission wavelengths are widely tunable from deep blue to yellow not only by the general acceptor strength due to the characters of heteroarene and CN‐substitution pattern but also by the subtle control of in‐acceptor conformation (twist angles). Small triplet‐to‐singlet energy gaps (ΔEST) and significant thermally activated delayed fluorescence (TADF) characteristics are obtained in a series of D–π–A compounds with sufficient acceptor strengths and tunable in‐acceptor conformation, yielding a series of efficient blue‐green to yellow TADF emitters with promisingly high photoluminescence quantum yields of 90%–100%. Highly efficient blue‐green to yellow TADF organic light‐emitting diodes (OLEDs) having external quantum efficiencies of up to 23.1%–31.3% are achieved using these efficient TADF emitters, which are among the most efficient TADF OLEDs ever reported.
Efficient blue‐green to yellow thermally activated delayed fluorescence emitters capable of generating 23%–31% electroluminescence external quantum efficiencies are developed adopting the acridine donor unit and cyano (CN)‐substituted pyridine and pyrimidine acceptor units. They permit systematic probing of influences of acceptor strengths and tunable conformations (twist angles) within the acceptor moieties through controlling the orientation of asymmetric heteroaromatic ring.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Artificial superlattices, based on van der Waals heterostructures of two-dimensional atomic crystals such as graphene or molybdenum disulfide, offer technological opportunities beyond the reach of ...existing materials. Typical strategies for creating such artificial superlattices rely on arduous layer-by-layer exfoliation and restacking, with limited yield and reproducibility. The bottom-up approach of using chemical-vapour deposition produces high-quality heterostructures but becomes increasingly difficult for high-order superlattices. The intercalation of selected two-dimensional atomic crystals with alkali metal ions offers an alternative way to superlattice structures, but these usually have poor stability and seriously altered electronic properties. Here we report an electrochemical molecular intercalation approach to a new class of stable superlattices in which monolayer atomic crystals alternate with molecular layers. Using black phosphorus as a model system, we show that intercalation with cetyl-trimethylammonium bromide produces monolayer phosphorene molecular superlattices in which the interlayer distance is more than double that in black phosphorus, effectively isolating the phosphorene monolayers. Electrical transport studies of transistors fabricated from the monolayer phosphorene molecular superlattice show an on/off current ratio exceeding 10
, along with excellent mobility and superior stability. We further show that several different two-dimensional atomic crystals, such as molybdenum disulfide and tungsten diselenide, can be intercalated with quaternary ammonium molecules of varying sizes and symmetries to produce a broad class of superlattices with tailored molecular structures, interlayer distances, phase compositions, electronic and optical properties. These studies define a versatile material platform for fundamental studies and potential technological applications.
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KISLJ, NUK, SBMB, UL, UM, UPUK
Self‐assembled monolayers (SAMs) offer the advantage of facile interfacial modification, leading to significant improvements in device performance. In this study, we report the design and synthesis ...of a new series of carboxylic acid‐functionalized porphyrin derivatives, namely AC‐1, AC‐3, and AC‐5, and present, for the first time, a strategy to exploit the large π‐moiety of porphyrins as a backbone for interfacing the indium tin oxide (ITO) electrode and perovskite active layer in an inverted perovskite solar cell (PSC) configuration. The electron‐rich nature of porphyrins facilitates hole transfer and the formation of SAMs, resulting in a dense surface that minimizes defects. Comprehensive spectroscopic and dynamic studies demonstrate that the double‐anchored AC‐3 and AC‐5 enhance SAMs on ITO, passivate the perovskite layer, and function as conduits to facilitate hole transfer, thus significantly boosting the performance of PSCs. The champion inverted PSC employing AC‐5 SAM achieves an impressive solar efficiency of 23.19 % with a high fill factor of 84.05 %. This work presents a novel molecular engineering strategy for functionalizing SAMs to tune the energy levels, molecular dipoles, packing orientations to achieve stable and efficient solar performance. Importantly, our comprehensive investigation has unraveled the associated mechanisms, offering valuable insights for future advancements in PSCs.
We have developed a series of new self‐assembled monolayers (SAMs) based on ZnII porphyrin for use as hole‐selective layer (HSL) in inverted perovskite solar cells (PSCs). Our study successfully demonstrates the superior performance of dual carboxylic acid functionalized porphyrins can boost the solar efficiency of PSCs. The outstanding performance of these porphyrin SAMs lies in their inherent self‐assembled properties and the presence of dual carboxylic acid groups that facilitate effective anchoring to both the ITO surface and perovskites.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Two–dimensional layered materials (2DLMs) have attracted considerable recent interest as a new material platform for fundamental materials science and potential new technologies. Here we report the ...growth of layered metal halide materials and their optoelectronic properties. BiI3 nanoplates can be readily grown on SiO2/Si substrates with a hexagonal geometry, with a thickness in the range of 10–120 nm and a lateral dimension of 3–10 µm. Transmission electron microscopy and electron diffraction studies demonstrate that the individual nanoplates are high quality single crystals. Micro‐Raman studies show characteristic Ag band at ≈115 cm−1 with slight red‐shift with decreasing thickness, and micro‐photoluminescence studies show uniform emission around 690 nm with blue‐shift with decreasing thickness. Electrical transport studies of individual nanoplates show n‐type semiconductor characteristics with clear photoresponse. Further, the BiI3 can be readily grown on other 2DLMs (e.g., WSe2) to form van der Waals heterostructures. Electrical transport measurements of BiI3/WSe2 vertical heterojunctions demonstrate p–n diode characteristics with gate‐tunable rectification behavior and distinct photovoltaic effect. The synthesis of the BiI3 nanoplates can expand the library of 2DLMs and enable a wider range of van der Waals heterostructures.
The synthesis of the BiI3 nanoplates can greatly expand the library of 2D layered materials to include a broad class of metal halides and enable metal halide‐based van der Waals heterostructures (e.g., BiI3/WSe2, BiI3/WS2) for exciting opportunities in electronics, optoelectronics, and hard radiation detectors.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Zwitterionic polymers exhibit excellent nonfouling performance due to their strong surface hydrations. However, salt molecules may severely reduce the surface hydrations of typical zwitterionic ...polymers, making the application of these polymers in real biological and marine environments challenging. Recently, a new zwitterionic polymer brush based on the protein stabilizer trimethylamine N-oxide (TMAO) was developed as an outstanding nonfouling material. Using surface-sensitive sum frequency generation (SFG) vibrational spectroscopy, we investigated the surface hydration of TMAO polymer brushes (pTMAO) and the effects of salts and proteins on such surface hydration. It was discovered that exposure to highly concentrated salt solutions such as seawater only moderately reduced surface hydration. This superior resistance to salt effects compared to other zwitterionic polymers is due to the shorter distance between the positively and negatively charged groups, thus a smaller dipole in pTMAO and strong hydration around TMAO zwitterion. This results in strong bonding interactions between the O– in pTMAO and water, and weaker interaction between O– and metal cations due to the strong repulsion from the N+ and hydration water. Computer simulations at quantum and atomistic scales were performed to support SFG analyses. In addition to the salt effect, it was discovered that exposure to proteins in seawater exerted minimal influence on the pTMAO surface hydration, indicating complete exclusion of protein attachment. The excellent nonfouling performance of pTMAO originates from its extremely strong surface hydration that exhibits effective resistance to disruptions induced by salts and proteins.
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IJS, KILJ, NUK, PNG, UL, UM
To clarify and verify the ultralow frequency (ULF) seismomagnetic phenomena, we have performed statistical studies on the geomagnetic data observed at the Kakioka (KAK) station, Japan, during ...2001–2010. We investigated the energy of ULF geomagnetic signals of the frequency around 0.01 Hz using wavelet transform analysis. To minimize the influences of artificial noises and global geomagnetic perturbations, we used only the geomagnetic data observed at nighttime (LT 2:30 A.M. to 4:00 A.M.) and utilized observations from a remote station, Kanoya, as a reference. Statistical results of superposed epoch analysis have indicated that ULF magnetic anomalies are more likely to appear before sizable earthquake events (Es > 108) rather than after them, especially 6–15 days before the events. Further statistical investigations show clearly that the ULF geomagnetic anomalies at KAK station are more sensitive to larger and closer events. Finally, we have evaluated the precursory information of ULF geomagnetic signals for local sizable earthquakes using Molchan's error diagram. The probability gain is around 1.6 against a Poisson model. The above results have indicated that the ULF seismomagnetic phenomena at KAK clearly contain precursory information and have a possibility of improving the forecasting of large earthquakes.
Key Points
Verify existence of ULF electromagnetic phenomena preceding large earthquakes
ULF geomagnetic anomalies are more sensitive to larger and closer events
ULF seismomagnetic phenomena obtained at KAK do contain precursory information
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
An earthquake of magnitude 9.0 occurred near the east coast of Honshu (Tohoku area), Japan, producing overwhelming Earth surface motions and inducing devastating tsunamis, which then traveled into ...the ionosphere and significantly disturbed the electron density within it (hereafter referred to as seismotraveling ionospheric disturbances (STIDs)). The total electron content (TEC) derived from nationwide GPS receiving networks in Japan and Taiwan is employed to monitor STIDs triggered by seismic and tsunami waves of the Tohoku earthquake. The STIDs first appear as a disk‐shaped TEC increase about 7 min after the earthquake occurrence centered at about 200 km east of the epicenter, near the west edge of the Japan Trench. Fast propagating disturbances related to Rayleigh waves quickly travel away from the epicenter along the main island of Japan with a speed of 2.3–3.3 km/s, accompanied by sequences of concentric circular TEC wavefronts and followed by circular ripples (close to a tsunami speed of about 720–800 km/h) that travel away from the STID center. These are the most remarkable STIDs ever observed where signatures of Rayleigh waves, tsunami waves, etc., simultaneously appear in the ionosphere.
Key Points
Ionospheric disturbances generated by earthquake and tsunami
Greatest disturbances ever seen containing signatures of following waves
Rayleigh, acoustic, and tsunami‐generated waves
Two-dimensional layered materials, such as molybdenum disulfide, are emerging as an exciting material system for future electronics due to their unique electronic properties and atomically thin ...geometry. Here we report a systematic investigation of MoS2 transistors with optimized contact and device geometry, to achieve self-aligned devices with performance including an intrinsic gain over 30, an intrinsic cut-off frequency fT up to 42 GHz and a maximum oscillation frequency fMAX up to 50 GHz, exceeding the reported values for MoS2 transistors to date (fT~0.9 GHz, fMAX~1 GHz). Our results show that logic inverters or radio frequency amplifiers can be formed by integrating multiple MoS2 transistors on quartz or flexible substrates with voltage gain in the gigahertz regime. This study demonstrates the potential of two-dimensional layered semiconductors for high-speed flexible electronics.
We report an efficient, highly selective modification on the N-terminal amines of peptides and proteins using aldehyde derivatives
reductive alkylation. After modification of a library of unprotected ...peptides XYSKEASAL (X varies over 20 natural amino acids) by benzaldehyde at room temperature, pH 6.1 resulted in excellent N-terminal selectivity (α-amino/ε-amino: >99 : 1) and high reaction conversion for 19 out of the 20 peptides. Under similar conditions, highly selective N-terminal modifications were achieved with a variety of aldehydes. Furthermore, N-termini of native peptides and proteins could be selectively modified under the same conditions to introduce bioorthogonal functional groups. Using human insulin as an example, we further demonstrated that preserving the positive charge in the N-terminus using reductive alkylation instead of acylation leads to a 5-fold increase in bioactivity. In summary, our reported method provides a universal strategy for site-selective N-terminal functionalization in native peptides and proteins.
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