Cryogenic‐Temperature Thermodynamically Suppressed and Strongly Confined CsPbBr₃ Quantum Dots for Deeply Blue Light‐Emitting Diodes

Abstract Suppressing the naturally ultrafast nucleation and growth rates of perovskite nanocrystals is a big challenge to develop high‐performance deeply blue perovskite light‐emitting diodes. Here, a cryogenic temperature thermodynamically suppressed synthetic strategy using liquid nitrogen is designed to obtain ultrasmall CsPbBr₃ quantum dots (QDs; ≈3 nm). Due to its strong confinement effect, the as‐obtained CsPbBr₃ QDs present strong deeply blue emission (≈460 nm) with a high quantum yield value of up to 98%, a large exciton binding energy of 301.6 meV, and excellent spectra stability for 60 d under atmosphere environment. This unprecedented regime indicates that cryogenic temperature can eliminate pre‐existing trap states and suppress the nonradiative process. Besides, the resultant perovskite light‐emitting diodes based on ultrasmall CsPbBr₃ QDs show deeply blue emission (≈ 460 nm) with a Commission Internationale de l'Eclairage (CIE) color coordinate of (0.145, 0.054), better than the blue National Television Standards Committee (NTSC) standard. Evidently, this cryogenic temperature synthetic strategy will pave the way for the large‐scale synthesis of the strongly confined ultrasmall quantum dots systems and open the door for the development of next generation solid‐state lighting and displays.