Sterically shielded p-type host via dual adamantane-based molecular engineering for high-efficiency exciplex emission

초록

The efficiency of exciplex host emission in thermally activated delayed fluorescence organic light-emitting diodes (TADF-OLEDs) is governed not only by electronic complementarity between p-type and n-type hosts but also by molecular structural factors that dictate the morphology of mixed thin films. However, the role of molecular structure in controlling intermolecular interactions and film morphology has received limited systematic attention. Here, we propose a molecular design strategy based on a sterically shielded p-type host that suppresses host self-aggregation and promotes homogeneous molecular mixing during vacuum deposition. A dual adamantane (Ad)-substituted carbazole host, AdCzCzPhAd, was designed and combined with a widely used n-type acceptor, SiTrzCz2. While the conventional p-type host CzCzPh exhibits favorable electronic properties, its relatively compact and pseudo-planar structure facilitates surface diffusion during co-deposition, leading to aggregation and enhanced nonradiative decay. In contrast, dual-Ad substitution introduces strong steric shielding while preserving the intrinsic photophysical characteristics of the parent host, effectively stabilizing an amorphous morphology and enabling uniform donor-acceptor distribution. As a result, the AdCzCzPhAd:SiTrzCz2 exciplex film exhibits a markedly enhanced photoluminescence quantum yield of approximately 50%, and green TADF-OLEDs employing this exciplex host achieve an external quantum efficiency of approximately 20%. These results demonstrate that steric shielding-induced morphology control of p-type hosts plays an important role in exciplex efficiency, establishing a widely applicable molecular design approach for high-performance vacuum-deposited TADF-OLEDs.

키워드