Tailoring structural rigidity utilizing a lock/unlock donor strategy for highly efficient solution processed blue and green HLCT OLEDs

Abstract

Highly efficient solution-processed HLCT OLEDs based on aromatic carbonyls are rarely reported, especially blue ones. In this pursuit, based on a twisted acceptor core, we designed and synthesized two unsymmetrical keto-carbonitrile emitters, namely, KCPhCz and KCPhDPA, utilizing a locked (carbazole) and unlocked (diphenylamine) donor strategy exhibiting color tunability. Additionally, we found that the insertion of a π-linker between the donor and acceptor converted an inefficient TADF emitter (KCCz, previously reported) into an efficient blue HLCT emitter (KCPhCz). We found this efficiency enhancement based on a weak carbazole donor was due to HLCT characteristics. KCPhCz and KCPhDPA-based molecules emitted in the blue and green regions respectively. Non-doped devices based on KCPhCz and KCPhDPA exhibited EQEs of 5.7 and 7.4%, respectively. The best performance was demonstrated by 7.5 wt% doped devices from both emitters. The KCPhDPA-based device showed a PE_max of 39.2 lm W⁻¹, a CE_max of 49.8 cd A⁻¹, and an EQE_max of 15.3% at a brightness of 100 cd m⁻² with CIE of (0.34, 0.58) and EL λ_max at 532 nm. In contrast, the KCPhCz-based optimized device showed a PE_max of 22.7 lm W⁻¹, a CE_max of 32.5 cd A⁻¹, and an EQE_max of 10.8% at a brightness of 100 cd m⁻² in the blue region with CIE of (0.18, 0.19) where EL showed λ_max at 480 nm.