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.