Flat panel displays enjoy 100 billion‐dollar markets with significant penetration in daily life, which require efficient, color‐saturated blue, green, and red light‐emitting diodes (LEDs). The recently emerged halide perovskites have demonstrated low‐cost and outstanding performance for potential LED applications. However, the performance of blue perovskite LEDs (PeLEDs) lags far behind red and green cousins, particularly for color coordinates approaching (0.131, 0.046) that fulfill the Rec. 2020 specification for blue emitters. Here, a high‐efficiency, lead‐free perovskite, CsEuBr3, is reported that exhibits bright blue exciton emission centered at 448 nm with a color coordinates of (0.15, 0.04), contributed from Eu‐5d→Eu‐4f/Br‐4p transition with an optical band gap of 2.85 eV. Further optical characterizations reveal its short excited‐state lifetime of 151 ns, excellent exciton diffusion diffusivity of 0.0227 cm2 s−1, and high quantum yield of ≈69%. Inspired by these findings, deep‐blue PeLEDs based on all‐vacuum processing methods, which have been demonstrated as the most successful approach for the organic LED industry, are constructed. The devices show a maximum external quantum efficiency of 6.5% with an operating half‐lifetime of 50 mins at an initial brightness of 15.9 cd m−2. It is anticipated that this work will inspire further research on lanthanide‐based perovskites for next‐generation LED applications.

With rapid advances of perovskite light-emitting diodes (PeLEDs), the large-scale fabrication of patterned PeLEDs towards display panels is of increasing importance. However, most state-of-the-art PeLEDs are fabricated by solution-processed techniques, which are difficult to simultaneously achieve high-resolution pixels and large-scale production. To this end, we construct efficient CsPbBr3 PeLEDs employing a vacuum deposition technique, which has been demonstrated as the most successful route for commercial organic LED displays. By carefully controlling the strength of the spatial confinement in CsPbBr3 film, its radiative recombination is greatly enhanced while the nonradiative recombination is suppressed. As a result, the external quantum efficiency (EQE) of thermally evaporated PeLED reaches 8.0%, a record for vacuum processed PeLEDs. Benefitting from the excellent uniformity and scalability of the thermal evaporation, we demonstrate PeLED with a functional area up to 40.2 cm2 and a peak EQE of 7.1%, representing one of the most efficient large-area PeLEDs. We further achieve high-resolution patterned perovskite film with 100 μm pixels using fine metal masks, laying the foundation for potential display applications. We believe the strategy of confinement strength regulation in thermally evaporated perovskites provides an effective way to process high-efficiency and large-area PeLEDs towards commercial display panels.

Violet light-emitting diodes (LEDs) are widely utilized for solid-state lighting, bacteria sterilization, and so on. Herein, the nontoxic and earth-abundant Ce 3+ ion with intrinsic strong violet emission is introduced to substitute Pb 2+ in CsPbBr 3 perovskite for electrically driven PeLEDs. Cs 3 CeBr 6 possesses a zero-dimensional photoactive site with a high photoluminescence quantum yield of ≈90% for both crystals and films. The excited-state lifetime of ≈28 ns enabled by the spin-and parity-allowed Ce-5d → Ce-4f transition is considerably faster than other lanthanide-based luminescent centers. The violet LEDs based on thermally evaporated Cs 3 CeBr 6 films display color-stable spectra with a maximum EQE of 0.46%, representing the first Cs 3 CeBr 6 LED and one of the most efficient violet PeLEDs. Moreover, a white LED with standard color coordinates of (0.339, 0.343) is constructed by combining Cs 3 CeBr 6 -based violet PeLEDs with yellow phosphor downconverters. Our work will motivate further exploration of diverse lanthanide-based perovskites for LEDs and other optoelectronics.

perspective. [1,14] The blue-emitting PeLEDs are indispensable for full-color displays and solid-state lighting, especially the pure blue emitting around 467 nm according to the National Television System Committee (NTSC) criterion. [15,16] Therefore, it is worthwhile for researchers to achieve pure blue-emitting PeLEDs.Two main strategies have been proposed to realize blue-emitting PeLEDs. Controlling quantum well structure provides a simple approach to tune the emission spectrum by engineering organic component composition. [17] For example, quasi-2D perovskite PEA 2 (Cs x MA 1−x ) n−1 Pb n Br 3n+1 can adjust the emission wavelength by controlling 〈n〉 value through partially replacing phenethylamine (PEA) by isopropylamine (IPA). [18] When the largest 〈n〉 value in the quantum well structure is tuned at 3 exactly, this perovskite film can exhibit 464 nm photoluminescence (PL), resulting in a low EQE of 0.15% with an EL peak at 474 nm due to lower conductivity of incorporated IPA than PEA. The 〈n〉 value = 3 is difficult to control, as the perovskite composition is not only affected by the spin-coating procedure, but also by the substrate, often resulting in a large distribution of 〈n〉 values.On the other hand, the mixed halide approach can achieve tunable emission from 450 to 490 nm with high photoluminescence quantum yields (PLQYs) by simply controlling Br/Cl ratio. [19] Yao et al. reported a 0.07% EQE of blue PeLEDs with an EL peak at 470 nm based on CsPbBr x Cl 3−x nanocrystals. [20] Congreve et al. improved EQE to 2.12% with an EL peak located at 466 nm by optimizing the device structure and Mn doping in CsPbBr x Cl 3−x nanocrystals. [21] Li et al. realized an efficient sky-blue PeLED with an EL peak located at 480 nm by incorporating PEABr to passivate CsPbBr x Cl 3−x film. [22] However, the strong working electric field (over a magnitude of 10 5 V cm −1 ) would prompt the halide-ion-migration-induced phase separation of mixed halide perovskite, which shifts the EL spectrum from target pure blue to longer wavelength. The spectral instability under working bias is the biggest challenge for mixed halide approach.According to our experience, it is easier and more controllable to achieve pure blue-emitting perovskite through the mixed halide approach than controlling quantum well structure. As for the spectral instability, the mixed halide perovskite film shows Cl-rich and Br-rich region under working bias due to the halide ions migration, and we found out that the process is Perovskite light-emitting diodes (PeLEDs) have attracted great research interests considering their excellent luminescent properties and solution processability. Despite rapid advances of green-, red-, and near-infraredemitting PeLEDs, blue-PeLEDs, as an essential part for full-color display and solid-state lighting, still remain challenging due to their low efficiency and spectral instability. Here, reported are spectrally stable blue-PeLEDs biased by an alternating voltage. First, 2-phenoxyethylamine-passivated CsPbBr x Cl 3−x is obtained...

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Next-generation wide color gamut displays require the development of efficient and toxic-free light-emitting materials meeting the crucial Rec. 2020 standard. With the rapid progress of green and red perovskite light-emitting diodes (PeLEDs), blue PeLEDs remain a central challenge because of the undesirable color coordinates and poor spectra stability. Here, we report Cs 3 CeBr x I 6− x ( x  = 0 to 6) with the cryolite-like structure and stable and tunable color coordinates from (0.17, 0.02) to (0.15, 0.04). Further encouraged by the short exciton lifetime (26.1 ns) and high photoluminescence quantum yield (~76%), we construct Cs 3 CeBr x I 6− x -based rare-earth LEDs via thermal evaporation. A seed layer strategy is conducted to improve the device’s performance. The optimal Cs 3 CeI 6 device achieves a maximum external quantum efficiency of 3.5% and a luminance of 470 cd m −2 with stable deep-blue color coordinates of (0.15, 0.04). Our work opens another avenue to achieving efficient and spectrally stable deep-blue LEDs.

With the rapid development of the panel display market, demand for efficient light emitters as active layers in electroluminescence (EL) devices has significantly increased. Luminescent inorganic lanthanide compounds (ILCs) with a characteristic f−d transition are particularly preferred for EL devices because of their high photoluminescent quantum yield, short excited-state lifetime, tunable emission spectra, and high thermal stability. In this Perspective, we first present an overview of inorganic lanthanide compounds with an emphasis on the mechanisms and characteristics of f−d emission. Then, the comprehensive advances of lanthanide element-doped inorganic compounds for EL study in recent decades are summarized. Moreover, the recent progress in directly employing ILCs for EL applications and rational improvement strategies in EL performance are highlighted. Last, we summarize the current challenges and opportunities of ILC-based EL devices as well as future improvement directions.

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