Dibenzothiophene-Based Phosphine Oxide Host and Electron-Transporting Materials for Efficient Blue Thermally Activated Delayed Fluorescence Diodes through Compatibility Optimization

Thermally activated delayed fluorescence (TADF) organic light-emitting diodes arise from the development of high-performance host materials and carrier transporting materials fitting for TADF dyes with optimized respective properties and interplays, making simultaneous performance improvement and device structure simplification feasible. In this work, a highly efficient blue TADF diode with simplified four-layer structure was successfully achieved by utilizing bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS) as blue emitter, 4,6-bis(diphenylphosphoryl)dibenzothiophene (DBTDPO) as host, and 4,6-bis(diphenylphosphoryl)dibenzothiophene sulfone (46DBSODPO) as electron-transporting layer. The compatibilities between DBTDPO and DMAC-DPS and DBTDPO and 46DBSODPO were optimized with respect to configuration, polarity, energy level, and interfacial interaction, resulting in the unchanged roughness of ∼0.25 nm before and after doping, high photoluminescence quantum yield over 85%, and reduced interfacial exciplex emissions. With the similar triplet excited energy (T₁) of ∼3.0 eV but inferior electrical properties compared to its analogues 28DBSODPO and 37DBSODPO, besides the homogeneity with DBTDPO, 46DBSODPO suppressed the formation of interfacial exciplex and dipole for efficient exciton confinement and electron injection and transportation, in virtue of the steric effects of its ortho-substituted phosphine oxide groups. Consequently, DBTDPO and 46DBSODPO endowed their DMAC-DPS based four-layer devices with the state-of-the-art performance, for example, the maximum external quantum efficiency over 16%, which was more than two-fold of those of conventional electron-transporting material 1,3,5-tri[(3-pyridyl)-phen-3-yl]benzene (TmPyPB). This design strategy about material compatibility could pave a way for developing high-performance blue TADF diodes with simplified configurations.