Revival of Degraded CsPbI ₃ Nanocrystals by Diselenide Ligand and Nanocrystal Self‐Assembly on Nanofibrilar Ligand Template

Abstract Among the lead halide perovskite (LHP) family, CsPbI ₃ is known to be significantly vulnerable to moisture, which hinders its use in real device applications. It is reported that chalcogen‐based ligands can better stabilize CsPbI ₃ and revive nanocrystals (NCs). Here, diphenyl diselenide (DPhDSe) ligand is used to revive the degraded CsPbI ₃ NCs through a post‐synthetic treatment of adding a small amount of DPhDSe in the degraded NC dispersion. DPhDSe in the dispersion formed nanofibrillar crystals at a low temperature through the π–π stacking of the phenyl ring. The nanofibrils played as a template on which the NCs self‐assembled and they are attached side‐by‐side to form microfibers. The microfiber powder containing the NCs is optically stable at ambient conditions and morphologically self‐healable by mild thermal annealing due to the dynamic Se─Se bond. The mechanism of the structural changes, optical transitions, and chemical changes has been systematically characterized through electron microscopy, diffraction, spectroscopy, and elemental analysis.