Benzo[b]furan-based host materials for blue fluorescent emitter to achieve an external quantum efficiency of 6.6 % in organic light-emitting device

Abstract

Recently, much research effort has been devoted to design emitter molecules with high horizontal dipole ratios to enhance optical coupling output efficiency of organic light-emitting devices (OLEDs), while less attention focused on designing host material to endow it with favorable horizontal dipole orientation. Five host materials dBF-Ph, 4dBF-Cz, dBF-dCz, 3dBF-Cz and tBF-Ph have been developed for blue emitters employing benzo [b]furan as key constructing unit. The benzo [b]furan could endow the resulting host materials with bipolar charge transport characteristics, high singlet and triplet energy level due to its electron-withdrawing property and small conjugate length. When using our developed 2356fTPA-BF as blue fluorescent emitter (λ_em = 446 nm, Φ_PL = 98 %), the host materials 3dBF-Cz could adjust horizontal dipole ratios of blue emitter to be as high as 96 %. This enables blue fluorescent OLED to achieve an external quantum efficiency of 6.6 % and current efficiency of 5.9 cd A⁻¹, respectively. This research highlights the important role of the host molecular design for improving molecular horizontal dipole orientation, as well as promising potential of benzofuran as important building unit for realizing bipolar host materials.