Metal halide perovskites (MHPs) have emerged as new‐generation highly efficient narrow‐band luminescent materials with applications in various optoelectronic devices, including photovoltaics (PVs), light‐emitting diodes (LEDs), lasers, and scintillators. Since the demonstration of efficient room‐temperature electroluminescence from MHPs in 2014, remarkable progress has been achieved in the development and study of light‐emitting MHP materials and devices. While the device efficiencies of MHP LEDs (PeLEDs) have significantly improved over a short period of time, their overall performance has not reached the levels of mature technologies yet, such as organic LEDs (OLEDs) and quantum dot LEDs (QDLEDs), to enable practical applications. Many issues and challenges, including low operational stability, lack of efficient blue PeLEDs, and toxicity of MHPs, remain to be addressed. Herein, some of the most exciting progress achieved in the development of efficient and stable PeLEDs during the last few years are introduced, the main issues and challenges in the field are discussed, and the prospects on addressing these issues and challenges are provided. With continuous effort, the potential of PeLEDs to become a commercially available LED technology for display and lighting applications in the future looks optimistic.

Metal halide perovskite nanocrystals (NCs) have emerged as highly promising light emitting materials for various applications, ranging from perovskite light‐emitting diodes (PeLEDs) to lasers and radiation detectors. While remarkable progress has been achieved in highly efficient and stable green, red, and infrared perovskite NCs, obtaining efficient and stable blue‐emitting perovskite NCs remains a great challenge. Here, a facile synthetic approach for the preparation of blue emitting CsPbBr3 nanoplatelets (NPLs) with treatment by an organic sulfate is reported, 2,2‐(ethylenedioxy) bis(ethylammonium) sulfate (EDBESO4), which exhibit remarkably enhanced photoluminescence quantum efficiency (PLQE) and stability as compared to pristine CsPbBr3 NPLs coated with oleylamines. The PLQE is improved from ≈28% for pristine CsPbBr3 NPLs to 85% for EDBESO4 treated CsPbBr3 NPLs. Detailed structural characterizations reveal that EDBESO4 treatment leads to surface passivation of CsPbBr3 NPLs by both EDBE2+ and SO42– ions, which helps to prevent the coalescence of NPLs and suppress the degradation of NPLs. A simple proof‐of‐concept device with emission peaked at 462 nm exhibits an external quantum efficiency of 1.77% with a luminance of 691 cd m−2 and a half‐lifetime of 20 min, which represents one of the brightest pure blue PeLEDs based on NPLs reported to date.

potentials in terms of both performance and cost efficiency. Identifying new lowcost materials for high performance LEDs that can be facilely processed is of great interest scientifically and practically.Recently, metal halide perovskites and perovskite-related materials have emerged as new generation light emitting materials with remarkable and highly tunable optical properties. [8] To date, efficient near-infrared, red, green and blue perovskite LEDs have been demonstrated with external quantum efficiencies (EQEs) of up to 22.2%, [9] 24.4%, [10] 28.1%, [11] and 13.8%, [12] respectively. While perovskite LEDs have shown great potentials, lead containing devices represent a major environmental and health concern that could limit their wide commercialization. Moreover, most halide perovskites and perovskite-related structures are metastable under normal atmospheric conditions, which is another obstacle to achieve devices with long lifetimes. [1] In searching for efficient lead-free perovskite-related light emitting materials with high stability, great progress has been made on zero-dimensional (0D) organic metal halide hybrids (OMHHs), which contain light emitting metal halide polyhedra fully isolated and surrounded by bulky organic cations. [13] Due to the complete site isolation, 0D OMHHs possess a perfect "host-dopant" structure, with light emitting metal halide species periodically embedded in a large bandgap organic host matrix. [14] While high PLQEs of up to near-unity have been routinely achieved in numerous 0D OMHHs, their applications in electrically driven LEDs have been under explored with very few reports to date. [15] The poor conductivity and wide bandgap of organic cations are the major factors responsible for the inferior charge transport and energy level alignment in these low performance LEDs based on 0D OMHHs. [14] Here, we report a simple molecular engineering approach to addressing the issues of low conductivity and poor energy alignment in electrically driven LEDs based on 0D OMHHs. By introducing a simple organic charge transporting unit (phenylcarbazole) to previously studied triphenyl(9-phenyl-9H-carbazol-3-yl) phosphonium (TPP + ) cation, we have developed a semiconducting organic cation, triphenyl(9-phenyl-9H-carbazol-3-yl) phosphonium (TPPcarz + ). [16] A 0D OMHH TPPcarzSbBr 4 was then synthesized for the first time, in which light emitting

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X-ray scintillators based on organic chromophores have the potential to deliver low-cost radiation detection products with fast response signals. However, their relatively low performance compared with that of widely used inorganic scintillators in terms of X-ray attenuation and light output has limited their applications. Here we report a dramatically improved scintillation performance for a BODIPY dye, difluoro(4via sensitization by a 0D organic metal halide, tetraphenylphosphonium manganese bromide ((C 24 H 20 P) 2 MnBr 4 ). By blending PM 570 and (C 24 H 20 P) 2 MnBr 4 in an appropriate ratio together in a polydimethylsiloxane matrix, we prepare plastic scintillators to exhibit a more than 15-fold increment of radioluminescence from PM 570. Such an enhancement is attributed to the excellent X-ray scintillation property of (C 24 H 20 P) 2 MnBr 4 and the efficient energy transfer from (C 24 H 20 P) 2 MnBr 4 to PM 570. These multicomponent plastic scintillators also exhibit an excellent linear response to the X-ray dose rate and a low detection limit of 22.5 nGy s −1 .