Dual-Path Exciton Harvesting Guided by Molecular Packing and Orientation Achieves Highly Efficient Deep-Blue Emission.

Efficient and color-pure deep-blue organic light-emitting diodes (OLEDs) are of critical significance for next-generation display technologies, yet the realization remains challenging owing to the stringent requirements of wide bandgap emitters, inefficient exciton utilization, and pronounced efficiency roll-off. In this study, we proposed a dual-path exciton harvesting strategy that combines high-energy reverse intersystem crossing with triplet-triplet annihilation to improve exciton utilization. The new deep-blue emitter PChCz, based on the chrysene moiety, exhibits favorable high-energy reverse intersystem crossing from high-lying triplet states, enabling non-doped OLEDs with a peak external quantum efficiency of 21.3%. To alleviate triplet-polaron annihilation at elevated current densities, a co-deposited sensitizer is employed to reutilize low-energy triplet via the triplet-triplet annihilation mechanism, thereby further improving the external quantum efficiency to 25.5% with suppressed roll-off. Morphological analysis reveals that co-deposition enhances compositional homogeneity and optimizes molecular orientation, which are conducive to efficient energy transfer and light outcoupling. Supported by rational molecular design and morphological control, the proposed dual-path exciton harvesting mechanism presents an effective approach for the development of high-performance deep-blue OLEDs.