High-Efficiency Near-Infrared OLED Enabled by Exciplex-Forming Hosts and a New Organic Fluorescent Emitter

Two blends comprising new dicyanopyrazine-based acceptors (m-CN and p-CN) and a carbazole-based donor CPTBF are explored for exciplex formation. The CPTBF:m-CN and CPTBF:p-CN blends show the signature red-shifted emission together with the delayed fluorescence observed in time-resolved measurement, manifesting the characteristics of thermally activated delayed fluorescence (TADF). The electroluminescence (EL) device employing CPTBF:m-CN (CPTBF:p-CN) blend as the emitting layer (EML) achieved an EQE of 5.22% (2.05%) with the EL λ_max centered at 607 nm (625 nm). The exciplex excitons can be efficiently extracted by a new benzobisthiadiazole-based near-infrared (NIR) emitter DCzPBBT, where a device is configured with CPTBF:m-CN: (5 wt.%) DCzPBBT as the EML to achieve a high EQE of 5.32% and an EL λ_max 758 nm. Further increase of the doping concentration to 10 wt.% of DCzPBBT exhibits a bathochromic shifted EL λ_max to 772 nm with 94% spectral coverage in the NIR (>700 nm) region, while the device EQE retains at 4.06%. The superior device performance stems from the highly efficient energy transfer between the exciplex-forming host and NIR dopant together.