Narrow Band Organic Emitter for Pure Green Solution‐Processed Electroluminescent Devices with CIE Coordinate y of 0.77

Abstract While the development of solution‐processed organic light‐emitting diodes (sOLEDs) utilizing multiple resonance‐induced thermally activated delayed fluorescence (MR‐TADF) is highly significant, it is restricted by the limited solubility and film‐forming property resulting from the rigid conjugate and planarity of MR‐TADF materials. Herein, an effective strategy is presented to obtain solution‐processed narrowband emitters by introducing an inert steric bulky hindrance group into the multiple resonance skeleton, thereby mitigating issues arising from intermolecular packing‐induced poor solution processing ability and quenching effects. The resulting target emitter, designed as 3CzSF‐BN, exhibits pure‐green emission with a peak at 520 nm and a small full width at half maximum (FWHM) of 30 nm (0.14) eV. Remarkably, it achieves an exceptional photoluminescence quantum yield (PLQY) of 100% and notable advancements in solution processing attributes. The optimized bottom‐emitting sOLED (BE‐sOLED) device achieves an external quantum efficiency (EQE) over 20% with Commission Internationale de I’Éclairage (CIE) coordinates of (0.214, 0.716). Notably, the top‐emitting sOLED (TE‐sOLED) device exhibits an ultra‐pure green color with FWHM of 22 nm and CIE coordinates of (0.138, 0.771), thereby highlighting the effectiveness of this strategy in designing high‐performance solution‐processed MR‐TADF materials.