High-Efficiency Exciplex-Based White Organic Light-Emitting Diodes with a New Tripodal Material as a Co-Host
The exciplex-forming co-hosts have been reported to be potentially suitable host for organic light-emitting diodes (OLEDs). However, it might not be able to achieve optimal low voltage and maximal power efficiency (PE), when it comes to white organic light-emitting diodes (WOLEDs). Herein, a novel strategy called multi-exciplex-forming co-hosts (MEHs) is introduced to achieve enhanced efficiency with low operating voltage. To realize this strategy, a new tripodal bipolar compound CNTPA-DPA was synthesized and used as a co-host in the devices. As a result, the orange light-emitting component in the WOLEDs reaches 27% in external quantum efficiency (EQE), 2.1 V in turn-on voltage, and 115.5 lm W-1 in PE, which is among the best values of orange color emission in OLEDs. And then this orange light emitting component was adopted in the MEHs strategy to construct WOLEDs, achieving 19.5% of EQE and 73 lm W-1 of PE at the maximum, which are 45.7% and 19.6% higher than those of using a single exciplex as the host, respectively. Moreover, the well-matched energy alignment endows the device with a very low operating voltage of 3.8 V at 1000 cd m-2. These results indicate that the performance of the exciplex-based WOLEDs can be remarkably enhanced by using the strategy of MEHs.