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Metal‐halide perovskite light‐emitting diodes (PeLEDs) have shown great advancement in green, red, and near‐infrared regions with external quantum efficiencies (EQEs) exceeding 20%. However, blue PeLEDs, an essential part of displays and lightings, show limited progress compared to the other color counterparts. Herein, a highly efficient pure‐blue PeLED is demonstrated by leveraging a novel CsPbBrxCl3‐x/Cs4PbBrxCl6‐x nanocomposite perovskite film as an emissive layer. The Cs4PbBrxCl6‐x phase, the derived phase of CsPbBr3 perovskite with a mixed halide system, effectively passivates defects in CsPbBrxCl3‐x, leading to high luminescence efficiency due to the significant reduction of nonradiative recombination. Furthermore, experimental and computational results confirmed that the compositionally optimized nanocomposite layer possesses a shallower valence band maximum (≈5.5 eV) than the pristine perovskite layer (≈5.9 eV), which is very advantageous in hole injection for device operation. The combined effects of the CsPbBrxCl3‐x/Cs4PbBrxCl6‐x nanocomposite render the fabricated blue PeLED to exhibit a pure‐blue emission at 470 nm with a maximum EQE of 5.3%. [ABSTRACT FROM AUTHOR]

The vertical alignment of liquid crystals (LCs) on cetyltrimethylammonium bromide-coated (CTAB-coated)indium tin oxide (ITO) glass is the consequence of specific interactions between the LCs, CTAB and ITO surface. The CTAB concentration influences the LC orientation, which changes the ITO surface energy. Changes in the surface energy of CTAB-coated ITO glass are investigated by the Owens–Wendt method. Both polar- and dispersive-component energies on the ITO surface decrease as the CTAB concentration increases, and reach saturation around 0.002% CTAB. The physico-chemical interaction between the LCs and the ITO surface was diminished by the presence of the CTAB layer, which induced the vertical alignment of LCs having positive or negative dielectric anisotropy. Vertical alignment is confirmed using crossed polarisers and the crystal rotation method. The electro-optical properties of fabricated reverse mode polymer dispersed liquid crystal films display transmittance ofTon: 29.7%,Toff: 85% and a response time ofτon: 33 ms,τoff: 107 ms. [ABSTRACT FROM AUTHOR]

Layered metal-halide perovskites, or two-dimensional perovskites, can be synthesized in solution, and their optical and electronic properties can be tuned by changing their composition. We report a molecular templating method that restricted crystal growth along all crystallographic directions except for [110] and promoted one-dimensional growth. Our approach is widely applicable to synthesize a range of high-quality layered perovskite nanowires with large aspect ratios and tunable organic-inorganic chemical compositions. These nanowires form exceptionally well-defined and flexible cavities that exhibited a wide range of unusual optical properties beyond those of conventional perovskite nanowires. We observed anisotropic emission polarization, low-loss waveguiding (below 3 decibels per millimeter), and efficient low-threshold light amplification (below 20 microjoules per square centimeter).

The morphology of perovskite films has a significant impact on luminous characteristics of perovskite light-emitting diodes (PeLEDs). To obtain a highly uniform methylammonium lead tribromide (MAPbBr 3 ) film, a gas-assisted crystallization method is introduced with a mixed solution of MAPbBr 3 precursor and polymer matrix. The ultrafast evaporation of the solvent causes a high degree of supersaturation which expedites the generation of a large number of nuclei to form a MAPbBr 3 -polymer composite film with full surface coverage and nano-sized grains. The addition of the polymer matrix significantly affects the optical properties and morphology of MAPbBr 3 films. The PeLED made of the MAPbBr 3 -polymer composite film exhibits an outstanding device performance of a maximum luminance of 6800 cd·m -2 and a maximum current efficiency of 1.12 cd·A -1 . Furthermore, 1 cm 2 area pixel of PeLED displays full coverage of a strong green electroluminescence, implying that the high-quality perovskite film can be useful for large-area applications in perovskite-based optoelectronic devices.