Synergistic ligand mediated anion exchange of CsPbI₃ quantum dots for high performance white LED and anti‐counterfeiting

Anion exchange is an effective strategy to regulate the composition and optoelectronic properties of perovskite quantum dots (PQDs). Though promising, it is more desirable to synthesize PQDs to avoid the decrease of photoluminescence quantum yield (PLQY). Herein, we developed a ligand mediated anion exchange approach, in which the phase transition from CsPbBr 3 QDs to CsPbI 3 QDs was observed with the introduction of N‐Acetyl‐ l ‐cysteine (NAC) and 1,3‐dimethylimidazolium iodide (DMII) aqueous solution in CsPbBr 3 QDs solution. NAC is expected to create more halogen vacancies in CsPbBr 3 QDs, which provides sufficient adsorption sites for I − ions, resulting in accelerating the anion exchange rate in the process of DMII incorporation. Benefiting from the synergistic ligand mediated anion exchange, high PLQY of 97% and remarkable stability of CsPbI 3 QDs are obtained. Furthermore, a white light‐emitting diode (WLED) with a lumen efficiency (LE) of 116.82 lm/W is constructed, showing remarkable stability under continuous operation.