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). Thus, expanding PHC materials into other types of OLEDs is critical for advancing organic electronics. In this study, we designed a series of 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 host in blue-emitting phosphorescence-sensitized multi-resonance thermally activated delayed fluorescence (MR-TADF) OLEDs. Devices based on 2,6-Bis(3,6-di-tert-butyl-9H-carbazol-9-yl)boron (DtBuCzB) emitter, using FIrpic or fac-Ir(tpz)3 as the sensitizer, achieved high maximum external quantum efficiency (EQEmax) 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 EQEmax of approximately 31% notably 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 hosts in phosphorescence-sensitized MR-TADF OLEDs, highlighting their potential as promising candidates for the next-generation of blue OLEDs.