Bulk Fabrication of Space‐Confined CsPbI ₃ Nanocrystal Films Toward Efficient and Bright Deep‐Red LEDs

Deep-red light-emitting diodes (LEDs) with 690-710 nm emission show high significance in optical, agricultural, and biomedical applications. As primary candidates for deep-red emitters, all-inorganic CsPbI₃ films suffer from fused large grains with abundant trap states, leading to inferior performance of deep-red perovskite LEDs (PeLEDs). Here we report CsPbI₃ nanocrystal films with strong space confinement and notable performance at ∼700 nm of deep-red emission via bulk fabrication. The dual roles of diaza-18-crown-6 dihydriodide additive as crystallization regulator and Lewis base ligand trigger more nucleation sites, retarded grain growth and passivated trap states, ensuring the crystallization of high-quality space-confined CsPbI₃ nanocrystal films. This approach establishes a record-high external quantum efficiency (EQE) of 23.4% for deep-red PeLEDs, and achieves a maximum luminance of 10152 cd m^-2. Low roll-off is also demonstrated that EQE maintain over 20% under a high current density of 900 mA cm^-2, which is superior to state-of-the-art deep-red organic and quantum-dot LEDs. The T₅₀ operating lifetime is estimated to be 234 h at an initial radiance of 6.3 W sr^-1 m^-2. This work provides an effectual strategy to accelerate radiative recombination and enhance the performance of CsPbI₃-based deep-red PeLEDs.