Tuning Ternary Deep Red Exciplex-Forming Hosts to Achieve a Stable OLED with EL Peak Centered at 834 nm

Abstract

This study explores new ternary exciplex-forming systems comprising a deep red-emitting CPF:58p-QN blend and various ratios of spacer TPF to optimize donor-acceptor interactions and exciplex characteristics. Time-resolved photoluminescence reveals delayed fluorescence of CPF:58p-QN:TPF blends, confirming the thermally activated delayed fluorescence (TADF) characters. By introducing different ratios of TPF, a progressive blueshift emission wavelength ranging from 696 nm (without TPF) to 659 nm (50 wt.% TPF) is observed. Notably, device A2, featuring CPF:58p-QN:TPF (2:2:1) blend as emitting layer, achieves a maximum external quantum efficiency (EQE(max)) of 2.13% with the electroluminescent peak (EL lambda(max)) centered at 672 nm. Moreover, a fluorescence emitter iCzPBBT is introduced as a dopant to realize a near-infrared (NIR) emissive device. Device B2, utilizing the CPF:58p-QN:TPF (2:2:1) blend as host doped with 5 wt.% iCzPBBT, exhibits an EQE(max) of 1.35% (EL lambda(max) = 848 nm), demonstrating effective energy transfer from exciplex to NIR dopant. Device C2 with a reduced amount of iCzPBBT (2 wt.%) to mitigate concentration quenching achieves an EQE(max) of 1.72% (EL lambda(max) = 834 nm) and good stability (LT90 > 88 h under a constant current density of 0.6 mA cm(-)(2)). This study underscores the potential of a ternary exciplex-forming system as a promising host for NIR OLED applications.