Pure Hydrocarbon Hosts Enabling Efficient Multi-Resonance TADF Blue-Emitting Organic Light-Emitting Diodes.

Pure hydrocarbon (PHC) materials are a class of highly efficient and stable host materials for organic light-emitting diodes (OLEDs), composed solely of carbon and hydrogen atoms. Despite recent great advancements in PHC research, their applications are still mainly limited to phosphorescent OLEDs (PHOLEDs). High-performance blue OLEDs still pose a considerable challenge. Thus, expanding PHC materials into other types of OLEDs is critical for advancing organic electronic technologies. In this study, we designed a series of original high-triplet PHC materials based on a multi-substitution approach of the 9,9'-spirobifluorene (SBF) backbone and used them, for the first time, as a host in phosphorescence-sensitized multi-resonance thermally activated delayed fluorescence (MR-TADF) OLEDs. Devices based on the 2,6-bis(3,6-di-tert-butyl-9H-carbazol-9-yl)boron (DtBuCzB) emitter, using FIrpic or fac-Ir(tpz) as the sensitizer, achieved high maximum external quantum efficiency (EQE) values ranging from 29.1 % to 33.9 %. Additionally, blue MR-TADF OLED devices based on v-DABNA with a phosphorescent sensitizer (CN-Ir), demonstrated outstanding electroluminescent performance, with an EQE of approximately 31 % due to an excellent molecular orientation induced by the PHC hosts. All devices exhibited narrow full-width at half-maximum spectra and minimal efficiency roll-off. This study marks the first application of PHC materials as hosts in phosphorescence-sensitized MR-TADF OLEDs, highlighting their potential as promising candidates for next-generation blue OLEDs and offering a viable pathway to achieve high-performance devices.