Donor extended blue TADF dendrimer for high-performance solution-processed OLEDs

Achieving efficient and stable blue solution-processed OLEDs remains an outstanding challenge in the field. We introduce a rational donor decoration strategy and apply it to the TADF emitter DOBNA-SpAc (aka. TDBA-SAF), exemplified in the emitter DOBNA-SpAc-DCz. By introducing ter(tert-butylcarbazole) units at the 2 and 7 positions of the acridine moiety, solubility and hole-transport properties are improved without compromising the blue emission endemic to DOBNA-SpAc. This emitter has a high photoluminescence quantum yield, Φ_PL, of 93% in 20 wt.% doped films in PPF (2,8-bis(diphenyl-phosphoryl)-dibenzo[b,d]furan), a very small singlet-triplet energy gap (ΔE_ST = 0.01 eV), and thus fast reverse intersystem crossing (k_RISC > 1 × 10⁶ s⁻¹), resulting in a short delayed lifetime of 2 µs. Solution-processed OLEDs with DOBNA-SpAc-DCz reached a maximum external quantum efficiency, EQE_max, of 29.4 ± 0.1% at CIE coordinates of (0.145, 0.211). By probing different electron transport materials and comparing to devices using DOBNA-SpAc, we found that the introduction of carbazole substituents promotes improved hole transport and a more spatially distributed recombination zone, while the faster k_RISC suppresses triplet-related annihilation processes. These results demonstrate that the targeted peripheral donor dendron decoration of spiroacridine-based TADF emitters is an effective strategy to achieve highly efficient emitters suitable for solution-processed OLED applications.