An HBr‐assisted slow cooling method is developed for the growth of centimeter‐sized Cs4PbBr6 crystals. The obtained crystals show strong green photoluminescence with absolute photoluminescence quantum yields up to 97%. More importantly, the evolution process and structural characterizations support that the nonstoichiometry of initial Cs4PbBr6 crystals induce the formation of nanosized CsPbBr3 nanocrystals in crystalline Cs4PbBr6 matrices. Furthermore, high efficiency and wide color gamut prototype white light‐emitting diode devices are also demonstrated by combining the highly luminescent Cs4PbBr6 crystals as green emitters and commercial K2SiF6:Mn4+ phosphor as red emitters with blue emitting GaN chips. The optimized devices generate high‐quality white light with luminous efficiency of ≈151 lm W−1 and color gamut of 90.6% Rec. 2020 at 20 mA, which is much better than that based on conventional perovskite nanocrystals. The combination of improved efficiency and better stability with comparable color quality provides an alternative choice for liquid crystal display backlights.

Because of the superior optical properties and potential applications in display technology, colloidal synthesis of halide perovskite quantum dots has been intensively studied. Although great successes have been made in the fabrication of green emissive CH 3 NH 3 PbBr 3 quantum dots, the fabrication of stable iodide-based CH 3 NH 3 PbI 3 quantum dots remains a great challenge because of their sensitivity to moisture in the open air. Even in a glovebox, the colloidal CH 3 NH 3 PbI 3 quantum dots obtained from N,N-dimethylformamide suffer from instability caused by fast degradation within days to weeks. In this work, we investigated the interactions between perovskite precursors and various polar solvents as well as their influence on the crystallization of CH 3 NH 3 PbI 3 in reprecipitation synthesis. By gaining chemical insight into the coordination effects, we can explain the degradation of CH 3 NH 3 PbI 3 to the defective crystals with coordinated solvents on the surface and/or intrinsic inner iodine vacancies. On the basis of this understanding, we fabricated air-stable CH 3 NH 3 PbI 3 quantum dots with a tunable size from 6.6 to 13.3 nm by selecting noncoordinated acetonitrile as a good solvent through ligand-assisted precipitation synthesis. The fabrication can be processed under ambient conditions, and the resulting CH 3 NH 3 PbI 3 quantum dots exhibit tunable emission with high photoluminescence quantum yields (maximum of ∼46%) as well as good stability. Moreover, the quantum confinement effects in CH 3 NH 3 PbI 3 quantum dots were discussed by correlating the size-dependent photoluminescence properties with theoretical calculations, which can be described by the infinite quantum well approximation model.

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Metal halide perovskites are emerging as new generation optoelectronic materials due to their high carrier mobility, long carrier diffusion length and large light absorption coefficient, which have broad applications in solar cell, light-emitting diode, laser, photodetector and transistors. Perovskite single crystal is an ideal platform for discerning the intrinsic properties of these materials. In some cases, perovskite single crystals are better candidates to gain high performance optoelectronics. However, the growth of perovskite single crystals is time and cost consuming, which has an obvious disadvantage for device exploration. Therefore, fast growth technique is highly desirable in not only promoting the use of perovskites in commercial applications but also facilitating deep physical investigation of the materials. In this review, we summarize thoroughly the development of fast growth of the halide perovskites single crystal. Specifically, we highlight the progress of rapid growth techniques with emphasis on the optimization control.

Here, we fabricated Cs-rich and Pb-rich Cs4PbBr6 samples with green photoluminescence emission and investigated the difference between them. Both Cs-rich and Pb-rich Cs4PbBr6 samples show strong green emissions at about 520 nm; however, the photoluminescence excitation properties of the green emission are greatly different from each other in the ultraviolet region. The photoluminescence excitation spectra of the Cs-rich sample have a broad excitation band from 334 to 500 nm. In comparison, the Pb-rich sample has two additional excitation bands of 250–300 and 324–334 nm. By correlating the experimental data with the theoretical calculations, the green photoluminescence emission can be attributed to the embedded CsPbBr3 nanocrystals, and the interlayer between Cs4PbBr6 and CsPbBr3 nanocrystals plays an important role in determining their photoluminescence excitation properties. It was proposed that the existence of the CsBr interlayer between the Cs4PbBr6 matrix and embedded CsPbBr3 nanocrystals block the electron transfer of excited Cs4PbBr6 and induce photoluminesence quenching under excitation of 250–300 nm.