Spectroscopic Insight into Customized Iodine Ligands Passivated Red-Emitting CsPb(Br,I)₃ Perovskite Nanocrystals via Time-Resolved Photoluminescence

Molecular engineering toward the structure of a passivation ligand is essential to improve the photoluminescence (PL) efficiency of perovskite nanocrystals (PNCs). To establish the surface recovery mechanism of red-emitting CsPb(Br,I)(3) NCs with PbI2 additives in the presence of a tightly bound passivation layer, time-resolved photoluminescence (TRPL) measurements and their chemometric analysis are employed. Two quaternary alkylammonium ligands, didodecyldimethylammonium iodide (DDAI) and tridodecylmethylammonium iodide (TDAI), are used to form a passivation layer, and then their role in the surface defects recovery is investigated by varying the amount of PbI2 additives. It is found that the structural difference between DDAI and TDAI can affect the accessibility of PbI2 additives to surface defects. The TRPL spectra analysis reveals that the ligand passivation with DDAI does not induce discernible lifetime enhancement with using PbI2 additives, but only a non-radiative pathway is gradually accelerated with increasing the amount of them. The TDAI ligand, however, shows the opposite behavior to give the best PL performance with a distinct molar ratio of TDAI:PbI2, even though the passivation itself gives a lower PL performance. It is argued that the intrinsic structural properties of the TDAI ligand are responsible for the effective surface recovery with the additives.