Strongly‐Confined CsPbBr3 Perovskite Quantum Dots with Ultralow Trap Density and Narrow Size Distribution for Efficient Pure‐Blue Light‐Emitting Diodes

Abstract The development of pure‐blue perovskite light‐emitting diodes (PeLEDs) faces challenges of spectral stability and low external quantum efficiency (EQE) due to phase separation in mixed halide compositions. Perovskite quantum dots (QDs) with strong confinement effects are promising alternatives to achieve high‐quality pure‐blue PeLEDs, yet their performance is often hindered by the poor size distribution and high trap density. A strategy combining thermodynamic control with a polishing‐driven ligand exchange process to produce high‐quality QDs is developed. The strongly‐confined pure‐blue (≈470 nm) CsPbBr 3 QDs exhibit narrow size distribution (12% dispersion) and are achieved in Br‐rich ion environment based on growth thermodynamic control. Subsequent polishing‐driven ligand exchange process removes imperfect surface sites and replaces initial long‐chain organic ligands with short‐chain benzene ligands. The resulting QDs exhibit high photoluminescence quantum yield (PLQY) to near‐unity. The resulting PeLEDs exhibit a pure‐blue electroluminescence (EL) emission at 472 nm with narrow full‐width at half‐maximum (FWHM) of 25 nm, achieving a maximum EQE of 10.7% and a bright maximum luminance of 7697 cd m −2 . The pure‐blue PeLEDs show ultrahigh spectral stability under high voltage, a low roll‐off of EQE, and an operational half‐lifetime (T 50 ) of 127 min at an initial luminance of 103 cd m −2 under continuous operation.