Enhanced triplet-triplet fusion for high efficiency and long lifetime of multiresonant pure blue organic light emitting diodes

Multiresonant (MR) narrowband emitters became extensive attention as a blue fluorescent dopant for organic light-emitting diodes (OLEDs) due to their high color purity and large photoluminescence quantum yields (PLQY), but they show poor operational lifetime. Herein, we present a double emissive layer (DEML) architecture to enhance the efficiency and lifetime of pure blue fluorescent OLEDs for MR type emitters. Mainly the DEML are divided into recombination zone and triplet–triplet fusion (TTF) zone based on different triplet energy hosts. Notably, we achieved a tremendous TTF ratio of 32.4% for MR-type dopant, which is close to the theoretical maximum of 37.5%. Furthermore, fabricated fluorescent devices based on DEML structure manifested tremendous maximum external quantum efficiency (EQEmax) of nearly 11% and revealed a longer lifetime (LT95) of 79 h at 1000 cd/m2 due to efficient triplet harvesting, which is almost double compared to the single host device. We believe that our findings can pave the way for enhancement in EQE and lifetime for blue OLEDs.