Owing to the enlarged exciton binding energy and the ability to confine charge carriers compared to their three-dimensional (3D) counterparts, research on quasi-two-dimensional (quasi-2D) perovskite materials and the correlative application in light-emitting diodes (LEDs) has attracted considerable attention. However, high density of defects, exciton emission trapping, and unbalanced charge injection are still the main intractable obstacles to their further development and practical application. Herein, we report an efficient multifunctional interlayer, lithium fluoride (LiF), to boost the performance of green-emitting quasi-2D perovskite LEDs (PeLEDs) by simultaneously overcoming the aforementioned issues. The introduced LiF interlayer not only eliminates the defects at perovskite grain boundaries and the surface by reinforcing the chemical bonds with uncoordinated lead ions but also restrains the emission of perovskite from quenching triggered by the electron transport layer and reduces excess electron injections to effectively balance carriers in the device. As a result, the resulting green quasi-2D PeLED shows a maximum external quantum efficiency of 16.35%, which is the best value obtained for quasi-2D perovskite-based LEDs reported so far, with simultaneous improvement in the operating lifetime of the device.

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and excellent charge-transport capabilities. [1][2][3][4][5] These exceptional properties have also made perovskites suitable for applying to light-emitting diodes (LEDs). [6] Since the first demonstration of hybrid organicinorganic CH 3 NH 3 PbBr 3 perovskite LED (PeLED) in 2014, [7] PeLEDs have rapidly attracted a great deal of attention from both academic and industrial researchers. [8][9][10] So far, the highest external quantum efficiency (EQE) for hybrid organic-inorganic PeLED can reach 11%. [11] However, hybrid organicinorganic perovskite materials suffer from the stability issue, which is a hurdle for the widespread use. Alternatively, all-inorganic perovskites (e.g., CsPbX 3 , X = I, Br, and Cl or mixed halide) possess superior thermal stability than their hybrid counterparts. [12][13][14] Besides, all-inorganic perovskites can exhibit high photoluminescence quantum yield (PLQY, e.g., > 90% in solution) and narrow emissions (e.g., full width at halfmaximum (FWHM) < 30 nm), and are compatible with the solution processing technology, which triggers intense interest in applying all-inorganic perovskites to develop LEDs since the first report of all-inorganic PeLED with a maximum EQE of 0.12% by Adopting proper electron transport layers (ETLs) is essential to high-performance all-inorganic perovskite light-emitting diodes (PeLEDs). However, the effect of ETLs has not been comprehensively investigated in all-inorganic nanocrystal PeLEDs, while 2,2′,2′′-(1,3,5-benzenetriyl) tris-[1-phenyl-1H-benzimidazole] (TPBi) is the most common ETL. Herein, a novel strategy is proposed to enhance the efficiency of nanocrystal PeLEDs. Tris(8-hydroxyquinoline) aluminum (Alq 3 ) is incorporated into TPBi to form a new ETL TPBi/ Alq 3 /TPBi, simultaneously enabling charge balance and confinement. The green PeLED with new ETL exhibits a maximum external quantum efficiency(EQE) of 1.43%, current efficiency of 4.69 cd A −1 , and power efficiency of 1.84 lm W −1 , which are 191%, 192%, and 211% higher than those of PeLEDs with conventional ETL TPBi, respectively. Significantly, the EQE is 36-fold higher than that of PeLED with high electron mobility ETL. Impressively, the full width at half-maximum of electroluminescence emission is 16 nm, which is the narrowest among CsPbBr 3 PeLEDs. The findings may present a rational strategy to enhance the device engineering of all-inorganic PeLEDs. Perovskite LEDsLead halide perovskites have recently emerged as a new family of optoelectronic materials for applications including solar cells, lasers, and photodetectors because of their impressive characteristics including narrow emission, size-tunable optical bandgaps,The ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Significant advancements in perovskite light-emitting diodes (PeLEDs) based on ITO glass substrates have been realized in recent years, yet the overall performance of flexible devices still lags far behind, mainly being ascribed to the high surface roughness and poor optoelectronic properties of flexible electrodes. Here, we report efficient and robust flexible PeLEDs based on a mixed-dimensional (0D−1D−2D−3D) composite electrode consisting of 0D Ag nanoparticles (AgNPs)/1D Ag n a n o w i r e s ( A g N W s ) / 2 D M X e n e / 3 D p o l y ( 3 , 4ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS).Our designed MXene-based electrodes combine the advantages of facile formation of a film of low-dimensional materials and excellent optical and electrical properties of metal, inorganic, and organic semiconductors, which endow the electrodes with high electrical/thermal conductivity, flexibility, a smooth surface, and good transmittance. Consequently, the resulting flexible PeLEDs (without a light-coupling structure) demonstrate a record external quantum efficiency of 16.5%, a high luminance of close to 50000 cd/m 2 , a large emitting area of 8 cm 2 , and significantly enhanced mechanical stability.