Linker aggregation engineering of TADF materials to tune carrier balance for highly efficient organic LEDs with long operational lifetime

Thermally activated delayed fluorescence (TADF) molecules are regarded as promising materials for realizing high-performance organic light-emitting diodes (OLEDs). The connecting groups between donor (D) and acceptor (A) units in D-A type TADF molecules could affect the charge transfer and luminescence performance of TADF materials in aggregated states. In this work, we design and synthesize four TADF molecules using planar and twisted linkers to connect the aza-azulene donor (D) and triazine acceptor (A). Compared with planar linkers, the twisted ones (Az-NP-T and Az-NN-T) can enhance A-A aggregation interaction between adjacent molecules to balance hole and electron density. As a result, highly efficient and stable deep-red top-emission OLEDs with a high electroluminescence efficiency of 57.3% and an impressive long operational lifetime (LT95 similar to 30,000 h, initial luminance of 1000 cd m-2) are obtained. This study provides a new strategy for designing more efficient and stable electroluminescent devices through linker aggregation engineering in donor-acceptor molecules. The carrier transport balance of donor-acceptor thermally activated delayed fluorescence molecules can be tuned by using planar and twisted linker units. And twisted ones can enhance acceptor aggregation interactions to accelerate charge transport between adjacent molecules, resulting in balanced carrier transport. Highly efficient and stable deep-red top-emission organic light-emitting diodes with an electroluminescence efficiency of 57.3% and an impressive long device lifetime LT95 similar to 30,000 h are obtained. image