Dipole-Dipole Interaction Management for Efficient Blue Thermally Activated Delayed Fluorescence Diodes

Thermally activated delayed fluorescence (TADF) diodes have emerged in recent years. However, blue devices still suffer from low luminance and serious efficiency roll-off, partially because of the utilization of unipolar host materials, which can suppress interaction-induced quenching at the cost of carrier flux unbalance. Herein, we demonstrate that the strong host excited-state dipole field can significantly worsen exciton quenching of blue TADF dopants through hostdopant dipole-dipole interactions. To integrate low excited-state polarity and ambipolar characteristics, we developed a donor-s-acceptor host with dramatically reduced excited-state dipole moments by one order of magnitude to only similar to 2 Debye, which gave rise to state-of-the-art external quantum efficiency beyond 20% from its devices, as well as record-low roll-off. Comparison between the device efficiencies of the hosts and various excited-state polarities revealed that the suppression of dipole-dipole interaction-induced quenching is the primary determinant of device performance for ambipolar blue TADF hosts.