4 years ago

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

Achieving Hybridized Local and Charge-Transfer Excited State and Excellent OLED Performance Through Facile Doping
Gan Chen, Jun Liu, Zihan He, Yongming Zhang, Wang Zhang Yuan, Yongyang Gong, Huili Ma, Gufeng He, Bingwu Wei, Xin Bin, Qian Peng, Yawei Lu
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 (EQEmax) 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 EQEmax 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. High efficiencies and maximal luminance are attained using doping to achieve the hybridized local and charge-transfer (HLTC) excited state and to prevent excimer formation for an AIEgen. Whilst the equivalent undoped organic light-emitting diodes (OLEDs) perform poorly, the doped devices demonstrate excellent performances with extremely low efficiency roll-off.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adom.201700466

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