Enhancing the stability of deep blue OLED via multiple exciton recycling channels provided by low-concentration doped TTF-HLCT combinational molecule

Currently, commercial deep blue organic light-emitting diodes (OLEDs) using triplet-triplet fusion (TTF) type emitting materials can only capture 50% of triplet (T₁) excitons, resulting in poor device efficiency. The utilization of nearly 100% excitons can be achieved by thermally activated delayed fluorescence (TADF) and hyperfluorescence strategy with narrowband blue emitters. However, the presence of high-energy T₁ excitons in the emitting layer (EML) typically results in inevitable molecule degradation, thereby limiting the device’s lifetime. To address this issue, a TTF-hybridized local and charge transfer (HLCT) combinational molecule is investigated in this work, aiming to enhance the stability of highly efficient deep blue OLED by reducing the density of T₁ excitons within EML through multiple exciton recycling channels. The utilization ratio of triplet excitons in EML can be enhanced by recycling T₁ excitons through the TTF process and high energy triplet (T_n) excitons through the HLCT process. Moreover, the low doping concentration of the TTF-HLCT molecule in the TADF system can mitigate the efficiency loss caused by the quenching of T₁ excitons. Finally, a top-emitting OLED with an external quantum efficiency of 25.9%, Commission Internationale de l’Eclairage (CIE) of (0.131, 0.050), and blue index of 312 cd A⁻¹ CIE_y⁻¹ are realized. Besides, the lifetime T₉₀@1000 cd m⁻² has been extended from 0.5 to 6.1 h. This work suggests the potential of the low doping concentration of a TTF-HLCT combinational molecule as a viable solution to address the stability issues encountered in deep blue OLEDs.