Interface dipole engineering at buried organic-organic semiconductor heterojunctions

A general technique for modifying energy level alignment at organic-organic heterojunctions is introduced, and is demonstrated here for phenyl-C ₆₁-butyric acid methyl ester (PCBM) and N,N′-Di-[(1-naphthyl)- N,N′-diphenyl]-1,1′-biphenyl)-4,4′-diamine (α-NPD). An ultra-thin layer (∼1 nm) of TiO₂ is used as an adhesion template to attach a self-assembled monolayer of dipolar phosphonate (PA) molecules to the lower interface of a two-stack ensemble. This modification induces shifts in the vacuum level and work function over ∼1.0 eV depending on the molecular dipole moment of the PA, which in turn modifies the electronic level alignment across the organic heterojunction interface by up to 0.5 eV.