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

Abstract

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 λmax 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 λmax 758 nm. Further increase of the doping concentration to 10 wt.% of DCzPBBT exhibits a bathochromic shifted EL λmax 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.