Organic acid-regulated self-assembly and anti-oxidation of low-defect Sn-Pb perovskite nanocrystals toward optical anti-counterfeiting applications

Tin-lead mixed perovskite nanocrystals (NCs) attract extensive research interest for narrow bandgap and low toxicity, yet inherent surface defects, weak crystallinity and easy Sn 2+ oxidation severely degrade their stability and usability. This work adopts four organic acids (FA, OA, CA, EDTA) with varied carboxyl numbers and coordination abilities to synthesize MAPb 0 . 5 Sn 0 . 5 Br 3 NCs and reveal carboxyl regulation mechanisms. Carboxyl groups coordinate more strongly with Sn 2+ than Pb 2+ , regulating the assembly of NCs and inhibiting Sn 2+ oxidation; hydrogen bonds between carboxyls and surface Br − drive ordered chain/sheet self-assembly and cut defect density. Citric acid (CA) shows the best modulation, owing to synergistic multi-carboxyl and hydroxyl structures enabling balanced surface coordination. CA-treated NCs possess outstanding stability against air, water, ethanol, heat and light. Using the differing thermal responsiveness of original and CA-modified NCs, stimulus-responsive optical anti-counterfeiting tags with dynamic encryption-decryption are fabricated. This study offers an effective route to low-defect Sn-Pb perovskite NCs and expands their applications in stable optoelectronics and advanced anti-counterfeiting.