Two-Channel Space Charge Transfer-Induced Thermally Activated Delayed Fluorescent Materials for Efficient OLEDs with Low Efficiency Roll-Off

Enhancing the reverse intersystem crossing (RISC) process of thermally activated delayed fluorescent (TADF) emitters is an effective approach to realize efficient organic light-emitting diodes (OLEDs) with low efficiency roll-off. In this work, we designed two novel TADF emitters, SATDAC and SATX-DAC, via a spiro architecture. Efficient maximum external quantum efficiencies (EQEs) of 22.6 and 20.9% with reduced efficiency roll-off (EQEs of 17.9 and 17.0% at 1000 cd m(-2)) were achieved via a two-RISC-channel strategy. X-ray diffraction shows close donor (D)/acceptor (A) spacing and suitable D/A orientation in crystals of the two emitters favoring both intra- and intermolecular through-space charge transfer (TSCT) processes. Transient photoluminescence decay measurements show that both emitters have two RISC channels leading to kISCT exceeding 10(6) s(-1). These results suggest that the two-RISC-channel design can be a novel approach for enhancing performance of TADF emitters, in particular at high excitation densities.

Automated summary

Enhancing the reverse intersystem crossing process of TADF emitters is an effective approach to achieve efficient OLEDs with low efficiency roll-off. The two novel TADF emitters designed in this work, SATDAC and SATX-DAC, showed efficient EQEs and reduced efficiency roll-off through a two-RISC-channel strategy. X-ray diffraction and transient photoluminescence decay measurements suggest that the design with two RISC channels can enhance the performance of TADF emitters, especially at high excitation densities.