Hyperbranched MR-TADF polymers with rigid-flexible balance engineering for solution-processed flexible narrowband OLEDs

Although multiple resonance thermally activated delayed fluorescence (MR-TADF) materials have emerged as a research hotspot in organic light-emitting diodes (OLEDs) due to their narrowband emission and high exciton utilization efficiency, their rigid planar structures hinder solution processability and flexible film fabrication. Herein, a “rigid-flexible balance” molecular engineering strategy is proposed to design and synthesize three-dimensional dendritic polymer materials for the first time, featuring MR-TADF units as the core and diphenyl fluorene as block units. The dendritic topology effectively suppresses intermolecular π-π stacking through steric hindrance from the block units, enhancing photoluminescence quantum yield to 60 % and reducing non-radiative transitions. The unique non-conjugated flexible linkage architecture not only preserves the high color purity of the deep blue MR core (CIE: 0.14, 0.12) but also significantly reduces backbone rigidity, endowing the material with superior solution processability and mechanical flexibility. This design, combined with PVK, can form excellent interloped films to further improve the device's stability under bending conditions, solving a key challenge for traditional rigid MR-TADF materials in flexible applications. The OLEDs based on this hyperbranched polymer exhibit a low turn-on voltage of 4.2 V, high external quantum efficiency (EQE) of 8.5 %, and narrow emission with FWHM of 52 nm. Remarkably, even after repeated bending of flexible devices, they retain an EQE of 5.9 % with maintained narrowband characteristics. This work provides an innovative solution to overcome the limitations of planar MR-TADF materials, highlighting the unique advantages of hyperbranched polymers in flexible OLEDs.