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All‐inorganic CsPbI3 perovskite semiconductor is attractive for deep‐red light‐emitting diodes (LEDs) because of its high photoluminescence, good thermal stability, excellent charge transport, and solution processability. However, the metastable phase of optically active CsPbI3 hinders the fabrication of efficient and bright deep‐red LEDs. Herein, a multifunctional ionic ligand regulation strategy using (2‐hydroxy‐5‐methylphenyl) triphenyl‐phosphonium iodide and 3‐(N, N‐dimethyloctylammonio) propanesulfonate is reported to regulate the optically active CsPbI3 crystallization and thus obtain high‐quality γ‐CsPbI3 thin films. The high crystallinity and preferential orientation of γ‐CsPbI3 arise from the strong bonding between the ionic ligands and ionic lead halide clusters. The obtained γ‐CsPbI3 thin films also possess suppressed defect densities, high luminescence, and high stability. Using this high‐quality thin film, an efficient and bright deep‐red LED with a peak external quantum efficiency of 13.34% and a maximum luminance of 2110 cd m−2 is successfully fabricated. The operational lifetime of the fabricated LED (time to half of the initial brightness, T50) reaches up to 40 min under a high current density of 50 mA cm−2 (corresponding to the initial brightness of 200 cd m−2). [ABSTRACT FROM AUTHOR]

Mixed halide perovskite nanocrystals show great promise for high-performance light-emitting diodes (LEDs) due to their tunable band gaps, high photoluminescence efficiency, and excellent color purity. However, one major challenge in using mixed halide CsPbBrxCl3–x NCs for pure blue LEDs is the instability of their electroluminescence (EL) caused by halide segregation. Here, we report an effective pseudohalide tetrafluoroborate (BF4–) passivation approach to improve the EL stability of CsPbBrxCl3–x NC-based LEDs. Our approach involves the solution-processed treatment of CsPbBrxCl3–x NCs by the complex of tributylphosphine oxide and calcium tetrafluoroborate, which yields pseudohalide BF4–-passivated CsPbBrxCl3–x NCs. The BF4– fills the surface halide ion vacancy, providing dual benefits of surface passivation and halide migration suppression. By using these BF4–-passivated CsPbBrxCl3–x NCs as the emitting layer, we have successfully fabricated spectrally stable and pure blue LEDs with an emission peak at 468 nm, a maximum luminance of 275 cd/m2, and a maximum external quantum efficiency of 3.2%. Our proposed BF4–-passivated NCs strategy will pave the way for the development of efficient, stable, and pure blue perovskite LEDs. [ABSTRACT FROM AUTHOR]

Metal halide perovskite light‐emitting diodes (PeLEDs) are promising high‐definition display candidates due to their narrow emission bandwidth and wide color gamut. However, efficient and stable pure‐red PeLEDs have rarely been achieved. Herein, a robust and strongly‐coordinated sulfate anion passivation strategy is reported to achieve a spectrally stable and efficient pure‐red PeLED with an electroluminescent peak at 630 nm and full width at half maximum of 27 nm. Octylammonium sulfate is employed to construct a PbSO4 layer on the surface of CsPbI3−xBrx nanocrystals, which can effectively inhibit phase separation under UV light, humidity, or heat treatment. Using sulfate passivated CsPbI3−xBrx NC film, pure red PeLEDs with high external quantum efficiency of 12.6%, excellent spectral stability, and an operational half‐life time of over 300 min (T50@100 cd cm−2) are fabricated. This work provides a new avenue to improve performance of pure red PeLEDs via strong‐coordinated sulfate passivation. [ABSTRACT FROM AUTHOR]

Lead halide perovskite nanocrystals (LHP NCs) are regarded as promising emitters for next-generation ultrahigh-definition displays due to their high color purity and wide color gamut. Recently, the external quantum efficiency (EQE) of LHP NC based light-emitting diodes (PNC LEDs) has been rapidly improved to a level required by practical applications. However, the poor operational stability of the device, caused by halide ion migration at the grain boundary of LHP NC thin films, remains a great challenge. Herein, we report a resurfacing strategy via pseudohalogen ions to mitigate detrimental halide ion migration, aiming to stabilize PNC LEDs. We employ a thiocyanate solution processed post-treatment method to efficiently resurface CsPbBr 3 NCs and demonstrate that the thiocyanate ions can effectively inhibit bromide ion migration in LHP NC thin films. Owing to thiocyanate resurfacing, we fabricated LEDs with a high EQE of 17.3%, a maximum brightness of 48000 cd m -2 , and an excellent operation half-life time.

All-inorganic CsPbI 3 perovskite is attractive for deep-red light-emitting diodes (LEDs) because of its excellent carrier mobility, high color purity, and solution processability. However, the high phase transition energy barrier of optically active CsPbI 3 black phase hinders the fabrication of efficient and bright LEDs. Here, we report a novel α-BaF 2 nanoparticle substrate-promoted solution-processable heteroepitaxial growth to overcome this hindrance and obtain high-quality optically active γ-CsPbI 3 thin films, achieving efficient and bright deep-red LEDs. We unravel that the highly exposed planes on the α-BaF 2 nanoparticle-based heteroepitaxial growth substrate have a 99.5% lattice matching degree with the (110) planes of γ-CsPbI 3 . This ultrahigh lattice matching degree initiates solution-processed interfacial strain-free epitaxial growth of low-defect and highly oriented γ-CsPbI 3 thin films on the substrate. The obtained γ-CsPbI 3 thin films are uniform, smooth, and highly luminescent, based on which we fabricate efficient and bright deep-red LEDs with a high peak external quantum efficiency of 14.1% and a record luminance of 1325 cd m -2 .

Metal halide perovskites are promising semiconductors for next-generation light-emitting diodes (LEDs) due to their high luminance, excellent color purity, and handily tunable band gap. However, it remains a great challenge to develop perovskite LEDs (PeLEDs) with pure red emission at the wavelength of 630 nm. Herein, we report a spectrally stable and efficient pure red PeLED by employing sequential ligand post-treated CsPbI 3 quantum dots (QDs). The synthesized CsPbI 3 QDs with a size of ∼5 nm are treated in sequential steps using the ligands of 1-hydroxy-3-phenylpropan-2-aminium iodide (HPAI) and tributylsulfonium iodide (TBSI), respectively. The CsPbI 3 QD films exhibit improved optoelectronic properties, which enables the fabrication of a pure red PeLED with a peak external quantum efficiency (EQE) of 6.4% and a stable EL emission centered at the wavelength of 630 nm. Our reported sequential ligand post-treatment strategy opens a new route to improve the stability and efficiency of PeLEDs based on QDs.