Efficient and Stable Ligand-Exchange Process Using Perovskite Nanocrystals Synthesized from a Liquid Crystalline Antisolvent.

Ligand exchange of perovskite nanocrystals (PNCs) is an essential process for optoelectronics applications, but it often causes structural instability and degradation of PNCs. In this work, we demonstrate that PNCs synthesized via ligand-assisted reprecipitation (LARP) using a liquid crystalline (LC) antisolvent, referred to as LC-LARP, enable a significantly more efficient and stable ligand-exchange process compared with those prepared by conventional LARP using toluene (T-LARP). After ligand exchange, PNCs from the LC-LARP (LC-PNCs) exhibit a dramatic increase in photoluminescence quantum yield (PLQY) from 29% to 80%, whereas PNCs from T-LARP (T-PNCs) show negligible improvement. Furthermore, LC-PNCs show exceptional stability under ligand-exchange reactions, retaining over 50% PLQY even at high ligand concentrations that trigger the complete decomposition of T-PNCs. This efficient and stable ligand exchange is attributed to superior ligand passivation and a low density of surface defects in LC-PNCs. Our approach is versatile and generalizable across diverse ligands and perovskite compositions. Finally, we demonstrate the practical utility of this method by designing LC-PNC-based light-emitting diodes (LEDs), which achieve a maximum external quantum efficiency (8.2%), significantly surpassing that of T-PNC-based LEDs (0.5%).