Inverted Tandem Phosphorescence Organic Light-Emitting Diodes Based on $\hbox {MoO}_{3}/\hbox {Al/Cs}_{2}\hbox {CO}_{3}$ Charge Generation Unit

A multilayer charge generation unit (CGU) MoO₃/Al/Cs₂CO₃ has been developed for inverted tandem organic light-emitting diodes (OLEDs). The current efficiency of inverted tandem phosphorescence OLED with MoO₃ (8 nm)/Al (1 nm)/ Cs₂CO₃ (0.5 nm) CGU is almost twice as high as that of individual electroluminescent (EL) device. Charges generate at hole-transporting host material/ MoO₃ interface and MoO₃ bulk layer, and electrons are extracted by Cs₂CO₃/electon-transporting layer (ETL) interface. The significantly enhanced performance of the tandem device with MoO₃/Al/Cs₂CO₃ CGU compared with a MoO₃/Cs₂CO₃-based one may be attributed to preventing chemical reaction of MoO₃ and Cs₂CO₃ by the inserted ultrathin Al layer. Moreover, the current efficiency and EL spectrum of another inverted tandem OLED combining red and green stack further prove the effective charge generation and separation with the multilayer MoO₃/Al/Cs₂CO₃ CGU. It is expected that such a CGU is a promising candidate for inverted tandem white OLED for active matrix organic light-emitting diode display driven by an n-type thin-film transistor backplane.