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Nitride perovskite LaWN3 has been predicted to be a promising ferroelectric material with unique properties for diverse applications. However, due to the challenging sample preparation at ambient pressure, the crystal structure of this nitride remains unsolved, which results in many ambiguities in its properties. Here, the authors report a comprehensive study of LaWN3 based on high‐quality samples synthesized by a high‐pressure method, leading to a definitive resolution of its crystal structure involving nitrogen deficiency. Combined with theoretical calculations, these results show that LaWN3 adopts an orthorhombic Pna21 structure with a polar symmetry, possessing a unique atomic polarization along the c‐axis. The associated atomic polar distortions in LaWN3 are driven by covalent hybridization of W: 5d and N: 2p orbitals, opening a direct bandgap that explains its semiconducting behaviors. The structural stability and electronic properties of this nitride are also revealed to be closely associated with its nitrogen deficiency. The success in unraveling the structural and electronic ambiguities of LaWN3 would provide important insights into the structures and properties of the family of nitride perovskites. [ABSTRACT FROM AUTHOR]

Ferroelectric materials have been a key research topic owing to their wide variety of modern electronic and photonic applications. For the quick exploration of higher operating speed, smaller size, and superior efficiencies of novel ferroelectric devices, the ultrafast dynamics of ferroelectrics that directly reflect their respond time and lifetimes have drawn considerable attention. Driven by time‐resolved pump‐probe spectroscopy that allows for probing, controlling, and modulating dynamic processes of ferroelectrics in real‐time, much research efforts have been made to understand and exploit the ultrafast dynamics of ferroelectric. Herein, the current state of ultrafast dynamic features of ferroelectrics tracked by time‐resolved pump‐probe spectroscopy is reviewed, which includes ferroelectrics order parameters of polarization, lattice, spin, electronic excitation, and their coupling. Several potential perspectives and possible further applications combining ultrafast pump‐probe spectroscopy and ferroelectrics are also presented. This review offers a clear guidance of ultrafast dynamics of ferroelectric orders, which may promote the rapid development of next‐generation devices. [ABSTRACT FROM AUTHOR]

On‐chip coherent light source has always been fascinating and intriguing due to its various potential applications. In the past decades, there has been some progress in the development of chip coherent light (e.g., nanolaser, Bose‐Einstein condensation and nonlinear optical effects). However, these methods strictly depend on materials and extreme experimental conditions, and are usually not tunable. Here, a hybrid structure is designed which combines a chirped surface plasmon metasurface with a monolayer transition metal dichalcogenide (TMDC) to achieve a coherent second harmonic generation (SHG) covering the entire visible light spectrum. Using only finite number of metallic grooves, a continuous resonance tuning is obtained. By translating the metasurface in space, a space‐frequency locking SHG is demonstrated. Although the Q factor of the surface plasmon cavity is low, its near‐field enhancements of both fundamental and SH waves are still obvious. Significantly, the broad linewidth of plasmonic cavity leads to a large degree of overlap between adjacent localized modes, that enables the tuning of the output wavelength continuously at room temperature. Meanwhile, the exciton resonance also plays an important role. This monolithic tunable device demonstrates the potentials of 2D material‐plasmon hybrid metasurface and to construct an efficient broadband tunable on‐chip coherent light source. [ABSTRACT FROM AUTHOR]

Two new bithiophene imide (BTI)-based n-type polymers were synthesized. f-BTI2-FT based on a fused BTI dimer showed a smaller band gap, a lower LUMO, and higher crystallinity than s-BTI2-FT containing a BTI dimer connected through a single bond. s-BTI2-FT exhibited a remarkable electron mobility of 0.82 cm2 V−1 s−1, and f-BTI2-FT showed a further improved mobility of 1.13 cm2 V−1 s−1 in transistors. When blended with the polymer donor PTB7-Th, f-BTI2-FT-based all-polymer solar cells (all-PSCs) attained a PCE of 6.85 %, the highest value for an all-PSC not based on naphthalene (or perylene) diimide polymer acceptors. However, s-BTI2-FT all-PSCs showed nearly no photovoltaic effect. The results demonstrate that f-BTI2-FT is one of most promising n-type polymers and that ring fusion offers an effective approach for designing polymers with improved electrical properties. [ABSTRACT FROM AUTHOR]

Unreacted lead iodide is commonly believed to be beneficial to the efficiency of methylammonium lead iodide perovskite based solar cells, since it has been proposed to passivate the defects in perovskite grain boundaries. However, it is shown here that the presence of unreacted PbI2 results in an intrinsic instability of the film under illumination, leading to the film degradation under inert atmosphere and faster degradation upon exposure to illumination and humidity. The perovskite films without lead iodide have improved stability, but lower efficiency due to inferior film morphology (smaller grain size, the presence of pinholes). Optimization of the deposition process resulted in PbI2 -free perovskite films giving comparable efficiency to those with excess PbI2 (14.2 ± 1.3% compared to 15.1 ± 0.9%) Thus, optimization of the deposition process for PbI2 -free films leads to dense, pinhole-free, large grain size perovskite films which result in cells with high efficiency without detrimental effects on the film photostability caused by excess PbI2 . However, it should be noted that for encapsulated devices illuminated through the substrate (fluorine-doped tin oxide glass, TiO2 film), film photostability is not a key factor in the device degradation. [ABSTRACT FROM AUTHOR]

At present, micro‐LED display, which inherit the high efficiency, the high Brightness, high reliability of OLED display, is one of the hottest and the most promising display techniques.i,ii,iii,iv The Indium selenide (In2Se3) based transistor which possess a high gain and a short response times not only broader the potential applications in photo detector, but also provides a platform for high performance active addressing drive circuits of Micro‐LED displays. Here we reported an ultrathinIn2Se3 thin film on silicon wafer and its fabrication process for field‐effect transistors. The In2Se3 flakes was exfoliated by Scotch tape and then transferred to a SiO2/Si substrate to fabricate field‐effect transistors (FETs). Fig. 1 (a) shows the model of the devices are fabricated using cleaved In2Se3 nanosheets on SiO2/Si substrates with the highly doped Si substrate used as the gate electrode. The Cr/Au was used as source/drain electrodes for the devices. [ABSTRACT FROM AUTHOR]

Two triimide‐functionalized n‐type acceptor polymers are designed and synthesized, which show narrower bandgap, lower‐lying frontier molecular orbital energy levels, and improved film morphology than the diimide‐functionalized analogue polymers. When blended with a p‐type donor polymer semiconductor PTB7‐Th, an outstanding power conversion efficiency of 8.98% with a remarkable open‐circuit voltage of 1.03 V is attained. This efficiency is among the highest values in all‐polymer solar cells (all‐PSCs) reported till today, surpassing that (6.85%) of the diimide‐functionalized analogue polymers by a big margin and even higher than that (8.69%) of the fullerene‐based solar cells. The results demonstrate that the triimide‐functionalized f‐BTI3 is an excellent building block for developing n‐type polymer semiconductors, and the polymer f‐BTI3‐T is among the best‐performing n‐type polymers for applications in all‐PSCs. The structure–property correlations of these imide‐functionalized polymer semiconductors offer important guides for developing high‐performance n‐type polymer semiconductors. [ABSTRACT FROM AUTHOR]