Inverted Tandem Phosphorescence Organic Light-Emitting Diodes Based on <formula formulatype="inline"><tex Notation="TeX">$\hbox{MoO}_{3}/\hbox{Al/Cs}_{2}\hbox{CO}_{3}$</tex> </formula> Charge Generation Unit

Abstract

A multilayer charge generation unit (CGU) $\hbox{MoO}_{3}/\hbox{Al/Cs}_{2}\hbox{CO}_{3}$ has been developed for inverted tandem organic light-emitting diodes (OLEDs). The current efficiency of inverted tandem phosphorescence OLED with $\hbox{MoO}_{3}$ (8 nm)/Al (1 nm)/ $\hbox{Cs}_{2}\hbox{CO}_{3}$ (0.5 nm) CGU is almost twice as high as that of individual electroluminescent (EL) device. Charges generate at hole-transporting host material/ $\hbox{MoO}_{3}$ interface and $\hbox{MoO}_{3}$ bulk layer, and electrons are extracted by $\hbox{Cs}_{2}\hbox{CO}_{3}$ /electon-transporting layer (ETL) interface. The significantly enhanced performance of the tandem device with $\hbox{MoO}_{3}/\hbox{Al/Cs}_{2}\hbox{CO}_{3}$ CGU compared with a $\hbox{MoO}_{3}/\hbox{Cs}_{2}\hbox{CO}_{3}$ -based one may be attributed to preventing chemical reaction of $\hbox{MoO}_{3}$ and $\hbox{Cs}_{2}\hbox{CO}_{3}$ 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 $\hbox{MoO}_{3}/\hbox{Al/Cs}_{2}\hbox{CO}_{3}$ 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.