Synergistic dual-functional passivation with formamidinium acetate for intrinsically stable CsPbBr₃ perovskite quantum dots synthesised in water

All-inorganic CsPbX₃ perovskite quantum dots (PQDs) exhibit outstanding optoelectronic properties but suffer from poor stability in water, which limits their practical applications. Despite progress in surface ligand engineering, the long-term durability of these PQDs remains challenging due to ligand desorption and subsequent degradation of the perovskite core. Herein, we report a one-pot aqueous-phase synthesis of highly water-stable CsPbBr₃ PQDs using formamidinium acetate (FAAc) as a dual-functional modifier. Formamidinium ions incorporate into the A-site, optimising the Goldschmidt tolerance factor and enhancing lattice integrity, whereas acetate ions serve as strongly bound surface ligands that suppress defect formation. The obtained PQDs exhibit a photoluminescence quantum yield of up to 91.6% and retain 60% of their initial emission intensity after 120 h of immersion in water. Additionally, the prepared PQDs were successfully applied to fabricate anti-counterfeiting patterns. This work provides a green synthetic route and insights into the design of intrinsically stable PQDs for practical optoelectronic applications.