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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]

Thermochromic phosphors are intriguing materials for realizing thermochromic behaviors of light‐emitting diodes. Here a highly luminescent and stable thermochromic phosphor based on one‐dimensional Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 is reported. This unique ionic copper‐iodine chain‐based hybrid exhibits near‐unity photoluminescence efficiency owing to the through‐space charge‐transfer character of relevant electronic transitions. More importantly, an alternative mechanism of thermochromic phosphorescence was unraveled, supported by a first principles simulation of concerted copper atom migration in the copper‐iodine chain. Furthermore, we successfully fabricate a bright thermochromic light‐emitting diode using this Cu4I6(4‐dimethylamino‐1‐ethylpyridinium)2 thermochromic phosphor. Our reported flexible ionic copper‐iodine chain‐based thermochromic luminescent material represents a new type of cost‐effective functional phosphor. [ABSTRACT FROM AUTHOR]