Highly efficient fluorescence/phosphorescence hybrid white organic light-emitting devices based on a bipolar blue emitter to precisely control charges and excitons†
Hybrid white organic light-emitting diodes (WOLEDs) combining blue fluorophores and green/red (or yellow) phosphors are still preferred for OLED production applications due to their advantages of good stability and high efficiency. One major challenge is to have a suitable blue fluorophore material to fully utilize the electrically generated excitons for fluorophore and phosphor emitters. Here, we employed an efficient blue fluorophore (PBI-PPI-TPA) with a high triplet energy of 2.48 eV as the blue emitter as well as the host for phosphors, whereby a series of highly efficient hybrid WOLEDs were successfully achieved. The two-color (BO) WOLEDs exhibited a maximum forward-viewing EQE/PE of up to 23.6%/77.8 lm W−1, and retained 20.0%/49.5 lm W−1 at 1000 cd m−2, thus exhibiting high-efficiency and low-efficiency roll-off. Furthermore, three-color (BYR) hybrid WOLEDs were also fabricated by adopting blue-yellow-red cascade energy transfer to ensure that all the excitons could be effectively utilized for the white emission. The resulting devices achieved a peak EQE/PE of 21.5%/53.2 lm W−1, retained 17.2%/26.8 lm W−1 at 1000 cd m−2, and the color rendering index (CRI) was doubled with respect to the two-color WOLEDs, showing a good trade-off between the efficiency and CRI. All these results are among the best reported for hybrid WOLEDs.