High-efficiency solution-processed triplet–triplet annihilation organic light-emitting diodes using oligocarbazole- and benzonitrile-modified polyaromatic blue fluorescent emitters

Abstract

Here, we report solution-processed non-doped triplet–triplet annihilation (TTA) organic light-emitting diodes (OLEDs). Three solution-processable blue emissive TTA molecules, namely CPhCN, CCsCN, and CAnCN, are designed and synthesized using polycyclic aromatic hydrocarbons of triphenylene (Ph), chrysene (Cs), and anthracene (An) as TTA emissive cores, asymmetrically substituted with oligocarbazole (C) and benzonitrile (CN), respectively. Experimental and theoretical investigations reveal that all molecules retain strong blue emissions with peaks at 460–470 nm, amorphous morphology with superior thermal stability, high-quality solution-cast thin films, decent hole mobility (1.19–4.74 × 10⁻⁷ cm² V⁻¹ s⁻¹), high-lying HOMO levels (−5.46 eV), and the lowest singlet (S₁)/triplet (T₁) excited states of 2T₁ > S₁ appropriate for the TTA process. They are successfully utilized as solution-processed non-doped emitters in simple structured TTA OLEDs. All solution-processed devices exhibit intense blue emissions (456–472 nm), low turn-on voltages (3.2–3.6 V), decent electroluminescence (EL) performances (EQE_max = 3.45–6.79% and CE_max= 3.55–6.50 cd A⁻¹), and TTA characteristics. Particularly, CCsCN-based TTA-solution processed OLEDs emit deep blue EL emission peaked at 456 nm with a high EQE_max of 6.79%. This work not only presents a new strategic design for the preparation of solution-processable TTA emitters, but also further ratifies that the TTA mechanism can also be effective in solution-processed OLEDs.