Metal halide perovskites are attracting great attention as next-generation light emitting materials due to their excellent emission properties with narrowband emission. [1][2][3][4] However, perovskite light-emitting didoes (PeLEDs) irrespective of their material types (polycrystals or nanocrystals) have not realized high luminance, high efficiency and long lifetime simultaneously, as they are influenced by the intrinsic limitations related to the trade-off properties between charge transport and confinement in each type of perovskite materials. [5][6][7][8] Here, we report an ultra-bright, efficient, and stable PeLEDs made of core/shell perovskite nanocrystals with a size of ~10 nm obtained using simple in-situ reaction of benzylphosphonic acid (BPA) additive with 3D polycrystalline perovskite films without separate synthesis process. During the reaction, large 3D crystals are split into nanocrystals and the BPA surrounds the nanocrystals, achieving strong carrier confinement. The BPA shell passivates the undercoordinated lead atoms by forming covalent bonds, and thereby greatly reduces trap density while maintaining good charge-transport properties of 3D perovskites. We demonstrate simultaneously efficient, bright, and stable PeLEDs that have maximum brightness of ~470,000 cd m -2 , maximum external quantum efficiency of 28.9 % (average = 25.2 ± 1.6 % over 40 devices), maximum current efficiency of 151 cd A -1 , and half-lifetime of 520 h at 1,000 cd m -2 (estimated half-lifetime >30,000 h at 100 cd m -2 ). Our work sheds great light on the possibility that PeLEDs can be commercialized in the future display industry.

This paper reports highly bright and efficient CsPbBr perovskite light-emitting diodes (PeLEDs) fabricated by simple one-step spin-coating of uniform CsPbBr polycrystalline layers on a self-organized buffer hole injection layer and stoichiometry-controlled CsPbBr precursor solutions with an optimized concentration. The PeLEDs have maximum current efficiency of 5.39 cd A and maximum luminance of 13752 cd m . This paper also investigates the origin of current hysteresis, which can be ascribed to migration of Br anions. Temperature dependence of the electroluminescence (EL) spectrum is measured and the origins of decreased spectrum area, spectral blue-shift, and linewidth broadening are analyzed systematically with the activation energies, and are related with Br anion migration, thermal dissociation of excitons, thermal expansion, and electron-phonon interaction. This work provides simple ways to improve the efficiency and brightness of all-inorganic polycrystalline PeLEDs and improves understanding of temperature-dependent ion migration and EL properties in inorganic PeLEDs.

Perovskite light-emitting diodes (PeLEDs) based on three-dimensional (3D) polycrystalline perovskites suffer from ion migration, which causes overshoot of luminance over time during operation and reduces its operational lifetime. Here, we demonstrate 3D/2D hybrid PeLEDs with extremely reduced luminance overshoot and 21 times longer operational lifetime than 3D PeLEDs. The luminance overshoot ratio of 3D/2D hybrid PeLED is only 7.4% which is greatly lower than that of 3D PeLED (150.4%). The 3D/2D hybrid perovskite is obtained by adding a small amount of neutral benzylamine to methylammonium lead bromide, which induces a proton transfer from methylammonium to benzylamine and enables crystallization of 2D perovskite without destroying the 3D phase. Benzylammonium in the perovskite lattice suppresses formation of deep-trap states and ion migration, thereby enhances both operating stability and luminous efficiency based on its retardation effect in reorientation.

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Tin-based perovskites have emerged as lead-free alternatives, but their application in perovskite light-emitting diodes (PeLEDs) has been limited due to the low chemical stability and inhomogeneity of the inorganic CsSnBr 3 films using solution processing. Here, we demonstrate bright (∼160 cd m −2 ) CsSnBr 3 PeLEDs made by introducing co-additives consisting of SnF 2 and a grain-growth inhibitor (1,3,5-tris(Nphenylbenzimidazol-2-yl)benzene). The use of co-additives increased the number of nucleation sites during the crystallization process of CsSnBr 3 , and consequently yielded uniform CsSnBr 3 films with decreased grain size and improved defect passivation. The crystallization-controlled CsSnBr 3 PeLEDs had a maximum luminance of ∼160 cd m −2 , i.e., ∼7500 times brighter than than that of the control devices (without additive, 0.02 cd m −2 ), and a long device lifetime of ∼30 h at 58 cd m −2 . Our work suggests that control of the crystallization of CsSnBr 3 during film formation is an important requirement to increase the luminescence efficiency and stability of tin-based PeLEDs.