Trap-Controlled Operational Stability in Dibenzofuran-Based Hosts for Blue TADF-OLEDs

Abstract

Stability remains the principal bottleneck for blue TADF-OLEDs, and it is strongly affected by the host response to electrical stress. Here we report a structure-property study of four hightriplet-energy dibenzofuran-biphenyl (DBF-BPh) hosts for stable blue TADF devices. DBF linkage position (2 vs 4) and tert-butyl substitution are exploited to tune solid-state charge dynamics within a chemically robust scaffold. All hosts exhibit high neat-film triplet energies (T₁ = 2.77-2.87 eV) suitable for blue/sky-blue exciton confinement, together with elevated multistate bond dissociation energies (BDEs) that exceed the fragility range typical of anionic C-N linkages in common carbazole-type hosts. In doped blue TADF-OLEDs, the 4-linked DBF-BPh hosts deliver the best overall device performance, reaching EQE_max = 23.5% with low efficiency roll-off and device lifetime LT₅₀ = 17.5 h at 1000 cd m^-2 (275 h at 100 cd m^-2). In contrast, tert-butyl-substituted hosts exhibit 2-4× shorter LT₅₀, despite comparable energetics and BDE profiles. Bias-dependent impedance spectroscopy combined with equivalent-circuit analysis indicates a larger resistive relaxation component in the tert-butyl hosts, consistent with increased trap-limited conduction and carrier accumulation, which accelerate exciton-polaron loss under operation. These results implicate trapping as a major contributor to device degradation in this DBF host series, thereby establishing trap suppression as a practical target for improving the lifetime of blue TADF-OLEDs.