Advances in light-emitting metal-halide perovskite nanocrystals
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Introduction Perovskites are a class of materials with the same structure as that of calcium titanate (CaTiO3), which was first discovered in 1839 by Gustav Rose and named after Russian mineralogist Lev Perovski. Since Miyasaka’s pioneering work in 2009 using organic metal-halide perovskites (MAPbBr3 and MAPbI3) as light absorbers in photovoltaic devices,1 metalhalide perovskites have received tremendous interest for a variety of applications, owing to their intriguing optical and electronic properties. The three-dimensional (3D) metal-halide perovskites possess a general formula of ABX3, where A is a monovalent cation with appropriate size, such as methylammonium (MA), formamidinium (FA), or Cs; B is a divalent cation, such as Pb and Sn; and X is a halide ion (i.e., Cl, Br, I, or their mixtures) (Figure 1a). With the incorporation of large organic cations (R), quasi-2D perovskites with chemical formula R2An−1BnX3n+1 could be formed, with metal-halide layers sandwiched between the organic layers. For the extreme case when only large organic cations are present (n = 1), layered-2D perovskites R2BX4 become available, as
shown in Figure 1b. Strictly speaking, these materials are not perovskites, as they do not have a 3D ABX3 structure. However, all of them contain layers of corner-sharing metalhalide octahedrons (BX6) with controlled thicknesses, and their properties are related to each other. Therefore, calling them quasi-2D and layered-2D perovskites is well accepted by the community. Metal-halide perovskites in the form of single crystals and polycrystalline thin films have been extensively investigated in photovoltaic cells and photodetectors because of their excellent light absorption, high charge-carrier mobilities, and exceptional defect tolerance. However, they are limited for light-emitting applications because of their low photoluminescence quantum efficiencies (PLQEs), a result of mobile ionic defects, and small exciton-binding energy.2,3 To achieve high PLQEs for metal-halide perovskites, the most effective approach is perhaps to form nanocrystals (NCs) with increased exciton-binding energy and reduced defects.4 Since the first report of highly luminescent perovskite NCs in 2014,5 tremendous research efforts have been expended on the development and study of perovskite NCs.
Liang-Jin Xu, Department of Chemistry and Biochemistry, Florida State University, USA; [email protected] Michael Worku, Materials Science and Engineering Program, Florida State University, USA; [email protected] Qingquan He, Department of Chemistry and Biochemistry, Florida State University, USA; [email protected] Biwu Ma, Department of Chemistry and Biochemistry, Florida State University, USA; [email protected] doi:10.1557/mrs.2020.143
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• VOLUME 45 • JUNE 2020Lund • mrs.org/bulletin © 2020 Materials Downloaded MRS fromBULLETIN https://www.cambridge.org/core. University Libraries, on 17 Jun 2020 at 13:14:47, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1557/mrs.2020.143
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