A spiro-silafluorene-phenazasiline donor-based efficient blue thermally activated delayed fluorescence emitter and its host-dependent device characteristics

We report a blue thermally activated delayed fluorescence compound based on a spiro-silicon-connected silafluorene-phenazasiline donor. By incorporating triphenyltriazine as an acceptor, the compound exhibited well-separated highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels and charge transfer-type emission, confirmed by density functional theory (DFT) calculations and its solvatochromic characteristics. The compound exhibited blue emission with a photoluminescence (PL) peak at 469 nm, a high photoluminescence quantum yield (PLQY) of 68%, and a single-triplet energy gap of 0.20 eV in a DPEPO host matrix. Due to its co-planar silafluorene and triphenyltriazine moieties, the compound exhibited a high horizontal emission dipole ratio of 79%. Various electroluminescent devices of single host, mixed host, and interface exciplex structures were fabricated using the compound as the emitter. The external quantum efficiency (EQE), maximum brightness, and Commission Internationale de L'Eclairage (CIE) y-values ranged from 0.63 to 20.6%, 210 to 6930 nit, and 0.120 to 0.206, respectively, depending on the host materials and device structures. Among the fabricated EL devices, the DPEPO host device exhibited the highest EQE of 20.6% with CIE color coordinates of (0.150, 0.184).