Strongly-Confined CsPbI3 Quantum Dots by Surface Cleaning-Induced Ligand Exchange for Spectrally Stable Pure-Red Light-Emitting Diodes with Efficiency Exceeding 26%

The advancement of pure-red perovskite light-emitting diodes (PeLEDs) is still a challenge because of surface "wastes" (like surface vacancies and excessive insulating ligands) on quantum dots (QDs). Herein, we develop a method to synthesize single-halide pure-red CsPbI3 QDs, combining a strong quantum confinement effect and meticulous surface-cleaning-induced ligand exchange. We achieve pure-red emitting QDs by controlling the size and uniformity under iodide-rich conditions. Subsequently, vacancy defects and insulating ligands are cleared through introducing acid. Then this surface-cleaning process induces ligand exchange to further inhibit the nonradiative recombination and improve the electrical property of QDs. These QDs show a pure-red photoluminescence (PL) at 635 nm with the PL quantum yield (PLQY) of 99%. Finally, PeLEDs, which utilize these QDs, demonstrate a pure-red electroluminescence (EL) peak at 638 nm with a maximum external quantum efficiency (EQE) of 26.0% and an excellent half-lifetime (T50) of 490 min at an original luminance of 102 cd/m2.