Donor Extended Blue TADF Dendrimer for High‐Performance Solution‐Processed OLEDs

ABSTRACT 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 (Δ E ST = 0.01 eV), and thus fast reverse intersystem crossing ( k RISC > 1 × 10 6 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.