Achieving Hybridized Local and Charge-Transfer Excited State and Excellent OLED Performance Through Facile Doping

Hybridized local and charge-transfer (HLCT) excited states provide a new avenue for achieving high yields of singlet excitons (>25%) and outstanding electroluminescence (EL) performance in organic light-emitting diodes (OLEDs). In this contribution, donor-acceptor (D-A) structured (Z)-2,3-bis[4-(diphenylamino)phenyl]acrylonitrile (BDPACS) with aggregation-induced emission (AIE) characteristics is demonstrated to possess HLCT excited states in low-polarity solvents and in vacuum-deposited neat films. However, undoped OLED devices of the same material show unexpectedly poor performances with external quantum efficiencies (EQE(max)) of at most 0.41%, due to the formation of exciplexes or excimers. To alleviate this, doped devices are fabricated using low-polarity 2-methyl-9,10-di(2-naphthyl)anthracene (MADN), which has the appropriate energy levels to serve as a host in the emissive layer and can eradicate exciplexes/excimers and moreover help achieve the HLCT state through the solid-state solvation effect. Such devices exhibit strikingly improved EQE(max) of 6.8%, as well as singlet utilization yields exceeding the theoretical limit of 25%. Furthermore, all doped devices exhibit extremely low efficiency roll-off. These results may have significant implications for the future fabrication of high-performance OLEDs based on AIE luminogens and HLCT emitters.