Joonghyuk Kim

The ongoing challenge in advancing organic light‐emitting diodes (OLEDs) is to mitigate performance degradation during operation, caused by the dissociation of molecular components and the ensuing defect formation. While defects can emerge throughout OLEDs with diverse detrimental effects, prior research has predominantly focused on those within the emission layer (EML), leaving other device areas unexplored. In this work, a previously overlooked, yet profound impact of defects in the hole transport layer (HTL) on charge and exciton dynamics in a phosphorescent OLED (PHOLED) is investigated. HTL defects confine and impede the injection of free holes into the EML, requiring an increased supply of electrons to maintain constant current in the device. Consequently, excitons become concentrated at the HTL/EML interface, leading to enhanced bimolecular annihilations and an 8% reduction in device efficiency. Furthermore, when HTL defects are within 8 nm from the interface, they can directly quench excitons, resulting in a substantial decrease in device efficiency by up to 76%. This defect‐induced exciton quenching occurs through both Dexter and Förster energy transfer, each with distinct distance dependence. The findings emphasize the necessity of preventing defect formation, particularly in proximity to the HTL/EML interface, to minimize efficiency degradation for PHOLEDs.

This research elucidates the effects of structural modulations on electroluminescent Au(I) complexes, shedding light on factors governing radiative and nonradiative processes. A series of Au(I) complexes, fortified with ortho ‐substituents in carbene and amido ligands, are subjected to rigorous structural, photophysical, and quantum chemical investigations, which unveil distinct structural and electronic effects exerted by the ligands. The investigations reveal that nonradiative processes are governed primarily by the energy‐gap law. Radiative processes are observed to have a weak correlation with the mutual interactions of the molecular orbitals of carbene and amido ligands. Rather, it is discovered that an accumulation of the negative charge in the Au 5 d orbital in the excited state decelerates radiative processes. The effectiveness of these findings is substantiated through the larger external quantum efficiency of electroluminescence devices employing the Au(I) complex, in comparison to those based on the archetypical Au(I) complex and the organic thermally activated delayed fluorescent molecule. These compelling revelations underscore the untapped potential of Au(I) complexes in the advancement of electroluminescence technology and advocate for continued investigations into the intriguing domain of ligand structural control.