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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]

Metal halide perovskites have gained huge research interest within few decades due to their optoelectronic applications. Recently, inorganic metal halide perovskites CsPbX3 (X = Cl, Br, I) has shown the improved stability with promising optical and electrical properties. We report the enhancement of PL intensity and the extension of carrier lifetime from strained CsPbBr3 microwires in air environment. PL intensity is enhanced more than fivefold for all the studied microwires under strain than the original. Maximum enhancement in PL intensity of more than 25-fold has been observed from a wire with lateral width of 630 nm. Based on the experiment and simulation results, we conclude that tensile strain can improve the oxygen adsorption by the defects on the surface of CsPbBr3 microwires, which will suppress the non-radiative transitions and enhance the light emission efficiency. These findings demonstrate that the strain engineering is an effective way to improve the performance of CsPbBr3 microstructures for optoelectronic applications. [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]