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 promis-
ing 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 (LT$_{95}$ ∼ 30,000 h, initial luminance of 1000
cd m$^{−2}$ ) are obtained. This study provides a new strategy for designing more effi-
cient and stable electroluminescent devices through linker aggregation engineering
in donor–acceptor molecules.