Insights into energy transfer pathways between the exciplex host and fluorescent guest: attaining highly efficient 710 nm electroluminescence
Journal
Journal of Materials Chemistry C
Journal Volume
8
Journal Issue
17
Pages
5704-5714
Date Issued
2020
Author(s)
Huang, C.-Y. et al.
Ho, S.-Y.
Lai, C.-H.
Ko, C.-L.
Wei, Y.-C.
Lin, J.-A.
Chen, D.-G.
Ko, T.-Y.
Zhang, Z.
Hung, W.-Y.
Abstract
Energy transfer between the exciplex host and fluorescent guest is a demanding process for attaining high-performance organic light-emitting diodes (OLEDs), particularly in the near-infrared (NIR) region, and insight into the dynamics of energy transfer has been elusive. In this study, new deep-red/NIR chromophores,NOz-TPAandNOz-t-TPAwhereNOzand TPA denote naphthobisoxadiazole and triphenylamine, respectively, have been developed with an electron donor-acceptor-donor (D-A-D) configuration. The optimized 1 wt% doped films forNOz-TPAandNOz-t-TPAblended with theTris-PCz:CN-T2T(1 : 1 in molar ratio) exciplex host showed similar deep red/NIR emissions with photoluminescence quantum yields (PLQY) of 42 (680 nm) and 28%, (709 nm), respectively. Comprehensive time-resolved measurements and dynamics analyses revealed significant differences in the energy transfer pathways,i.e.FörsterversusDexter-type energy transfer between the exciplex host and the fluorescent guest, in which the introduction of bulkytert-butyl groups in theNOz-t-TPAdoped film greatly suppressed the Dexter-type energy transfer pathway. Despite the lower PLQY, the analytical simulation predictedNOz-t-TPAto be a better candidate for realizing highly efficient electroluminescence. Confirmation was provided by the performance of theNOz-t-TPA-doped OLED, showing an external quantum efficiency (EQE) of 6.6% with peak wavelength at 710 nm, which is among the best records for the metal-free NIR OLEDs around 710 nm. Insight into energy transfer pathways thus plays a pivotal role in achieving the high-performance OLEDs that incorporate the exciplex host and fluorescent guest.
SDGs
Type
journal article