Electronic structures of MoO₃ -based charge generation layer for tandem organic light-emitting diodes

The role of MoO₃ in charge generation layers for tandem organic light-emitting diodes is investigated. The electronic structure of a typical MoO₃ -based charge generation layer, consisting of N, N′ -bis(1-naphthyl)- N, N′ -diphenyl- 1, 1′ -biphenyl- 4, 4′ -diamine, MoO₃, and Mg doped 4,7-diphenyl-1,10-phenanthroline (NPB/ MoO₃/Mg:Bphen) is identified to be a p/n/n junction. It is shown that MoO₃ can pronouncedly modify the energy level alignment, beneficial to charge separation at the NPB/MoO₃ interface and electron injection at the MoO₃/Mg:Bphen interface from MoO₃ into suitable molecular energy levels of adjacent emission units. Moreover, Mg:Bphen is favorable to block holes flowing from the anode side directly into the adjacent emission unit.