Dominant Parameters Affecting Device Durability for Blue TADF Molecules

Abstract Organic light‐emitting diodes (OLEDs) have achieved remarkable commercial success in displays for mobile phones and televisions, while blue OLEDs still have a drawback in triplet utilization. Hyperfluorescence OLEDs utilizing thermally activated delayed fluorescence (TADF) represent a promising technology for achieving high efficiency and color‐purity. However, their overall performance, including device durability, remains significantly below industrial requirements. In particular, one still has to face the lack of understanding of the relationship between the photophysical properties of TADF materials and their stability. To date, many studies have suggested that shorter exciton lifetimes, which suppress annihilation processes, can help enhance device lifetimes. In this work, however, the correlation between device lifetime and the photophysical properties of four TADF emitters is investigated and find a noticeable decrease in stability with increasing excited‐state energy levels, indicating that higher excited‐state energies (S₁+T₁ energies > 5.4 eV) have a substantial impact on device degradation. While improved color purity can be achieved by using a TADF assistant dopant with a shorter emission wavelength, the energy levels must be confined within a specific range to balance efficiency and device lifetime effectively. This study provides practical guidelines for improving device stability and performance.