Tailored ligand design enabling comprehensive passivation of perovskite nanocrystals for light-emitting diodes†

Ever since the emergence of perovskite nanocrystals (PeNCs), their unique properties have attracted significant attention in both practical and academic fields, precisely because the ligands accentuate these characteristics. There are many examples of improving the optical properties, dispersibility, and durability of PeNCs by designing the ligands, and the usefulness of ligand engineering has been demonstrated. However, due to the emergence of highly complex issues stemming from the crystal and surface states of PeNCs, the harnessing of ligand design for LEDs—one of the major applications of PeNCs—remains limited. In this study, we focused on three aspects of the ligand's molecular structure: the head, tail, and counter anion, and by designing a structure that assigns distinct roles to each component, we comprehensively passivated the surface of PeNCs, thereby enabling their application in LEDs. The designed ligands relieved the crystal strain on the PeNCs, reduced the electrical insulation, and improved the optical properties by providing an ideal chemical surface. As a result of the synergistic effects, the EQE exhibits a 2.3-fold enhancement over the control devices, achieving a high value of 17.6%. This study not only proposes a ligand-engineering approach but also highlights this strategy as a new frontier in PeNCs research.