Achieving 20% External Quantum Efficiency for Fully Solution-Processed Organic Light-Emitting Diodes Based on Thermally Activated Delayed Fluorescence Dendrimers with Flexible Chains.

Actualizing high-efficiency thermally activated delayed fluorescent (TADF) organic light-emitting diodes (OLEDs) with fully wet processes is of great significance to the development of purely organic electroluminescence and the application of large-area OLED displays. Herein, new strategies are proposed to develop the TADF dendrimers with tunable colors by adjusting the way of linking branches to the core and the numbers of peripheral branches. Due to an energy gradient and efficient exciton utilization in the core-dendron system, the solution-processed OLEDs with the four dendrimers 5CzBN-O-Cz, 5CzBN-O-2Cz, 5CzBN-Cz, and 5CzBN-2Cz all give rise to low turn-on voltages and great device efficiency. Notably, 5CzBN-2Cz affords record-high fully solution-processed TADF OLEDs with external quantum efficiency of above 20%, which is significantly comparable to the efficiency of TADF OLEDs based on vacuum deposition. The work offers a guideline for designing solution-processable materials, paving the way toward practical applications of large-area fully solution-processed OLEDs.