Performance optimization of solution-processed TADF-OLEDs using core-identical small, medium, and high molecular weight hosts†

The physical interactions between the host and emitter in solution-processed organic light-emitting diodes (OLEDs) significantly influence device performance. In this study, we designed and synthesized a novel solution-processable blue multi-resonance (MR) emitter, 4FlDABNA, which features narrow-band blue emission and excellent solubility with a sterically protected emissive core to mitigate aggregation-induced quenching. Using this bulky emitter, we investigated the effect of host materials with varying molecular weights (MWs) on OLED performance while maintaining a fixed conjugated core unit, CzCzPh. Three hosts were synthesized: CzCzPh-mAd (low-MW), Cy-2(Ph-mCzCz) (medium-MW), and P(Ph-mCzCz) (high-MW). All hosts shared the same CzCzPh core and exhibited similar energy levels and optical properties, as well as high triplet energy levels, making them compatible with blue emitters. OLEDs based on the low-MW CzCzPh-mAd and medium-MW Cy-2(Ph-mCzCz) outperformed those based on the high-MW P(Ph-mCzCz). Notably, the medium-MW host Cy-2(Ph-mCzCz) maintained stable device performance even under high-temperature drying conditions. These findings suggest that medium-MW Cy-2(Ph-mCzCz) provides an optimal balance between molecular stability, thin-film morphology, and device efficiency, making it a promising host for solution-processed MR-OLEDs.