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

ABSTRACT 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 CsPbI 3 films suffer from fused large grains with abundant trap states, leading to inferior performance of deep‐red perovskite LEDs (PeLEDs). Here we report CsPbI 3 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 CsPbI 3 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 T 50 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 CsPbI 3 ‐based deep‐red PeLEDs.