Sulfone-incorporated thermally activated delayed fluorescence emitters enable organic light-emitting diodes with low efficiency roll-off

Purely organic thermally activated delayed fluorescence (TADF) emitters have shown enormous potential yet still suffer from the serious efficiency roll-off in organic light-emitting diodes (OLEDs) due to the long exciton lifetimes, thus impeding the wide-range commercialization. In this work, phenothiazine dioxide is incorporated into the diphenyl sulfone derivatives to construct two novel emitters, namely 10-(4-((4-(9,9-dimethylacridin-10(9H)-yl)phenyl)sulfonyl)phenyl)-10H-phenothiazine 5,5-dioxide (DMAC-DPS-DOPTZ) and 10-(4-((4-(10H-phenoxazin-10-yl)phenyl)sulfonyl)phenyl)-10H-phenothiazine 5,5-dioxide (PXZ-DPS-DOPTZ). Heavy atom effect of sulfur (S) atom can efficiently improve the spin-orbit coupling (SOC) and accelerate the reverse intersystem crossing (RISC) process of the emitters. In addition, the S atom could promote intersystem crossing (ISC) channel. Expectedly, both emitters exhibit the tiny energy splitting (ΔEST = 0.03 eV) between the lowest excited single state (S1) and triplet state (T1). The short exciton lifetimes (τd = 3.2 μs) and rapid RISC rates (kRISC = 2.7 × 106 s−1) are realized without introducing noble metals, which demonstrate the efficient TADF. Moreover, the emitters display obvious aggregation-induced emission (AIE) property. The OLEDs fabricated with the emitters achieve a maximum quantum efficiency (EQE) of 11.7%. Significantly, even at a luminance of 1000 cd m−2, the device EQE is retained to be 10.1% for the device based on PXZ-DPS-DOPTZ emitter, which represents the extremely low efficiency roll-off among reported TADF OLEDs.