Complementary P = O…H and π-π interaction network enables synergistic exciton harvesting for high-efficiency white thermally activated delayed fluorescence diodes

Abstract

Wide-band emissions of conventional thermally activated delayed fluorescence (TADF) emitters with twisted intramolecular charge transfer (TICT) states are superior for realizing high-quality lighting. However, besides suppressing high-polarity TICT states induced exciton quenching, host matrixes are crucial for optimizing interactions in emissive layers for rational exciton allocation and utilization. Herein, we report an asymmetric phosphine oxide host named STSPO, whose 9,9′-spirobi[thioxanthene] (ST) core and diphenylphosphine oxide (DPPO) group are complimentary in balancing weak π-π interactions and intermolecular hydrogen bonds (IHB). As a result, besides favorable electron mobility (µ_e) of ∼ 10^-5 cm² V⁻¹ s⁻¹ and high-enough excited energy levels, STSPO facilitates uniform dispersions of blue and yellow TADF dopants, optimizes host-dopant and blue-to-yellow energy transfer, and supports direct carrier and exciton capture by yellow TADF emitters. Consequently, STSPO hosted single-emissive-layer complementary-white TADF devices realized the state-of-the-art performances, including external quantum efficiency and power efficiency up to 24.2 % and 82.9 lm/W, respectively.