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 (Delta E-ST = 0.03 eV) between the lowest excited single state (S-1) and triplet state (T-1). The short exciton lifetimes (tau(d) = 3.2 mu s) and rapid RISC rates (k(RISC) = 2.7 x 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.

Automated summary

In this study, two novel emitters were constructed by incorporating phenothiazine dioxide into diphenyl sulfone derivatives, which can significantly improve the efficiency roll-off issue in organic light-emitting diodes (OLEDs) at high brightness. The heavy atom effect of the sulfur (S) atom enhances the spin-orbit coupling and accelerates the reverse intersystem crossing (RISC) process of the emitters, while promoting the intersystem crossing (ISC) channel. The emitters exhibit efficient thermally activated delayed fluorescence (TADF) properties and obvious aggregation-induced emission (AIE) property. The OLEDs fabricated with these emitters achieve a maximum quantum efficiency (EQE) of 11.7%, and even at a luminance of 1000 cd m(-2), the device based on PXZ-DPS-DOPTZ emitter shows extremely low efficiency roll-off with an EQE of 10.1%.