Intrinsically Ionic, Thermally Activated Delayed Fluorescent Materials for Efficient, Bright, and Stable Light-Emitting Electrochemical Cells

Solid-state light-emitting electrochemical cells (LECs) using sustainable and eco-friendly materials and affording high brightness, efficiency, and stability are highly desired. Here, intrinsically ionic, thermally activated delayed fluorescence (TADF) materials 1-3 for efficient, bright, and stable LECs are reported. 1-3 feature carbazole-type donors and cationic triazine-type acceptors, which are located ortho to each other on the phenyl linkers. Through-space charge-transfer (CT) dominates the CT transitions in 1-3. In doped and neat films, 1-3 show blue and green TADF emission, respectively, with reverse intersystem crossing rates at around 7.0 x 10(5) s(-1). 1-3 possess excellent electrochemical stability (except for the oxidation of 1) and film-forming abilities. LECs using neat films of 1-3 as the single active layers afford green electroluminescence with peak brightness/peak external quantum efficiency (EQE) of up to 572 cd m(-2)/6.8% under 4.0 V and peak brightness/peak EQE/half-lifetime of up to 860 cd m(-2)/5.4%/48 h under 50 A m(-2). A longer half-lifetime of 218 h has further been achieved at 162 cd m(-2) under 10 A m(-2). The work reveals the bright prospect for the development of efficient, bright, and stable LECs with intrinsically-ionic TADF materials.

Automated summary

This study demonstrates the development of efficient, bright, and stable LECs using intrinsically-ionic TADF materials 1-3, showcasing excellent performance characteristics.