Sequential Fusion‐Volatilization Strategy for In Situ Growth of Perovskite Nanocrystals Enabling High‐Performance LEDs

Abstract In situ growth of perovskite nanocrystals (PNCs) in solid‐state films offers a compelling solution to the dual challenges of moisture sensitivity and defect‐mediated efficiency losses in perovskite light‐emitting diodes (PeLEDs). Moving beyond conventional ligand treatments that typically leave charge‐blocking residues, a sequential fusion‐volatilization approach employing octylammonium acetate (OAAc) is presented to fabricate phase‐pure cubic α‐FAPbI 3 PNC films. OAAc's unique thermal properties facilitate a self‐regulated two‐stage process: i) as a dynamic molten flux during annealing, it promotes crystalline perfection, while ii) its complete volatilization ensures residue‐free defect‐passivation. This intelligent design achieves simultaneous ligand purification (removing 100% non‐passivating species while retaining defect‐coordinated ones) and synergistic passivation of cationic and anionic defects, yielding remarkable performance in near‐infrared PeLED: a champion 23.03% external quantum efficiency with 30.2‐h operational half‐life ( T 50 ) at 100 mA cm −2 . This work establishes a novel paradigm for in situ fabrication of ligand‐engineered PNCs films, paving the way for next‐generation high‐performance PeLEDs.