DMAPbI ₃ ‐Enabled Synthesis of Stable CsPbI ₃ Nanocrystals for Light‐Emitting Diodes With 27.5% External Quantum Efficiency

The synthesis of perovskite nanocrystals for light‐emitting diodes typically employs poorly controlled ion‐mediated precipitation processes, suffering from low photoluminescence quantum yield (PLQY), inhomogeneous morphology, and poor stability. Herein, by adjusting the nucleation method with a new type of precursor, namely “DMAPbI 3 ”, high‐quality and low‐defect‐density perovskite CsPbI 3 nanocrystals were successfully synthesized, with PLQY of 93% emitting at 659 nm. Particularly, the CsPbI 3 nanocrystals exhibit enhanced environmental stability, maintaining ∼70% of their initial photoluminescence intensity after 6 h of UV irradiation exposure or 100°C aging. Utilized as the luminescent layer, the fabricated perovskite LED (PeLED) device shows a peak EQE of 27.5%, representing an almost two‐fold enhancement compared to 14.7% for the control PeLED device. This simple and efficient approach is well‐suited for large‐scale production and practical applications.