However, MR-TADF molecules generally have long exciton lifetimes, creating challenges for device stability, particularly in blue OLEDs. In the blue-emitting layer, the accumulation and collision of excitons can produce high-energy excitons, leading to chemical-bond dissociation. Therefore, efficiently utilizing excitons is crucial to achieve high-quality blue OLEDs.

In a study published in Advanced Materials, a research group led by Prof. LU Canzhong and Prof. CHEN Xulin from the Fujian Institute of Research on the Structure of Matter of the Chinese Academy of Sciences proposed and implemented a novel sensitization strategy termed doublet-sensitized fluorescence (DSF) to achieve high-performance deep-blue electroluminescence.

In the DSF-OLEDs, the researchers utilized Ce-2 as the sensitizer and the MR-TADF material v-DABNA as the terminal emitter to fabricate DSF-OLEDs. Since the generation of doublet excitons was not restricted by spin statistics and both doublet radiative transitions and energy transfer were free from spin-forbidden constraints, this strategy allowed for the efficient and rapid utilization of excitons.

Moreover, the researchers revealed that in the emitting layer of the DSF-OLEDs, the ground state of Ce-2 captured a hole, resulting in the formation of a Ce(IV) species, which then readily combined with an injected electron to form a doublet excited state, referred to as Ce(III)*. Subsequently, the energy of the doublet excitons was transferred to the first singlet excited state of the terminal emitter via efficient Förster resonance energy transfer (FRET), which occurred without the need for spin-flip. 

Unlike cases where some excitons were initially generated on the co-host during photoexcitation, in the DSF-OLED, excitons were predominantly generated on Ce-2. This lowered the ratios of triplet excitons and delayed fluorescence by avoiding triplet-triplet Dexter energy transfer (DET) from the co-host to 𝜈-DABNA.

This study highlights the potential of the DSF strategy in achieving efficient, stable, and high-color-purity blue OLEDs, making it promising for ultra-high-definition OLED display applications.