Perovskite Quantum Dots with Ultralow Trap Density by Acid Etching‐Driven Ligand Exchange for High Luminance and Stable Pure‐Blue Light‐Emitting Diodes

Abstract The research on metal halide perovskite light‐emitting diodes (PeLEDs) with green and infrared emission has demonstrated significant progress in achieving higher functional performance. However, the realization of stable pure‐blue ( ≈ 470 nm wavelength) PeLEDs with increased brightness and efficiency still constitutes a considerable challenge. Here, a novel acid etching‐driven ligand exchange strategy is devised for achieving pure‐blue emitting small‐sized ( ≈ 4 nm) CsPbBr 3 perovskite quantum dots (QDs) with ultralow trap density and excellent stability. The acid, hydrogen bromide (HBr), is employed to etch imperfect [PbBr 6 ] 4− octahedrons, thereby removing surface defects and excessive carboxylate ligands. Subsequently, didodecylamine and phenethylamine are successively introduced to bond the residual uncoordinated sites of the QDs and attain in situ exchange with the original long‐chain organic ligands, resulting in near‐unity quantum yield (97%) and remarkable stability. The QD‐based PeLEDs exhibit pure‐blue electroluminescence at 470 nm (corresponding to the Commission Internationale del'Eclairage (CIE) (0.13, 0.11) coordinates), an external quantum efficiency of 4.7%, and a remarkable luminance of 3850 cd m −2 , which is the highest brightness reported so far for pure‐blue PeLEDs. Furthermore, the PeLEDs exhibit robust durability, with a half‐lifetime exceeding 12 h under continuous operation, representing a record performance value for blue PeLEDs.