Efficient fluorescent white organic light-emitting devices with a reduced efficiency roll-off based on a blue ambipolar fluorescent emitter

• Efficient fluorescent white organic light-emitting devices were made.
• The efficiency roll-off and color coordinates stability were improved.
• Study on the role of ambipolar material in improving the efficiency roll-off.
• Research on improving the efficiency roll-off from internal structure of devices.

White organic light-emitting devices (WOLEDs) with fluorescent donor-acceptor-substituted spirobifluorene compounds (red 2-diphenylamino-7-(2,2-dicyanovinyl)-9,9′-spirobifluorene and blue 2-diphenylamino-7-(2,2-diphenylvinyl)-9,9′-spirobifluorene) have been fabricated. The optimized WOLEDs shows a maximum current efficiency 5.9 cd/A and very low efficiency roll-off. From the brightness at maximum current efficiency to high brightness of 10000 cd/m2, the current efficiency roll-off is only 0.4%. It can be attributed to the ambipolar blue fluorescent emitter with voltage-independnet mobility which makes the device having a broader charge recombination zone and balance of carrier transport.