Lateral current suppression in tandem organic light-emitting diodes by adopting a buffer layer

For the tandem organic light emitting diodes (TOLEDs) with the charge generation unit (CGU) of LiF/Al/MoO3, there is a significant current lateral spreading causing light emission over an extremely large area outside the OLEDs pixel, due to the conductive interfacial layer caused by the oxidation-reduction reaction between Al and MoO3 layers. To crack this nut, a buffer layer of 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HAT-CN) is inserted between Al and MoO3 layers. The result shows the HAT-CN buffer layer eliminates the spread light emission in the TOLEDs. What's more, the device characteristics show the new CGU of LiF/Al/HAT-CN/MoO3 has stronger charge generation and injection capabilities. The white TOLEDs with the new CGU exhibit a high external quantum efficiency (EQE) of 28.4%. Compared with the single OLEDs and the TOLEDs with the CGU of LiF/Al/MoO3, the efficiency is increased by 143% and 44%, respectively.