Silicon-based peripheral steric donor modifications for a high-efficiency multi-resonance thermally activated delayed fluorescence emitter

Abstract

Multi-resonance thermally activated delayed fluorescence (MR-TADF) emitters have broad applications in organic light-emitting diodes (OLEDs). However, their device performance is often limited by the large conjugated planarity that makes them easily aggregate in the form of π–π stacking, resulting in aggregation-caused quenching (ACQ) and the formation of excimers, which reduce exciton utilization efficiency and color purity. To address these issues, large shielding units can be incorporated to prevent interchromophore interactions. In this study, we introduced 10,10-diphenyl-5,10-dihydro-dibenzo[b,e][1,4]azasiline (DPPASi), which contains a silicon atom, at the para-carbon position of a B-substituted phenyl ring as a steric group to synthesize the emitter BNSi. This modification successfully achieved a narrow-band blue emission at high doping ratios with a maximum external quantum efficiency (EQE_max) of 34.8% in the corresponding OLED device. Even at luminance levels of 1000 cd m⁻², an impressive EQE of nearly 20% was maintained. This study provides valuable insights for designing efficient narrow band blue emitters by utilizing the steric effect.