Charge generation layers comprising transition metal-oxide/organic interfaces: Electronic structure and charge generation mechanism

The energetics of an archetype charge generation layer (CGL) architecture comprising of $4,4′,4″$-tris(⁠$N$-carbazolyl)triphenylamine (TCTA), tungsten oxide $(WO3)$⁠, and bathophenanthroline (BPhen) n-doped with cesium carbonate $(Cs2CO3)$ are determined by ultraviolet and inverse photoemission spectroscopy. We show that the charge generation process occurs at the interface between the hole-transport material (TCTA) and $WO3$ and not, as commonly assumed, at the interface between $WO3$ and the n-doped electron-transport material $(BPhen:Cs2CO3)$⁠. However, the n-doped layer is also essential to the realization of an efficient CGL structure. The charge generation mechanism occurs via electron transfer from the TCTA highest occupied molecular orbital level to the transition metal-oxide conduction band.