Interface dipole engineering at buried organic–organic semiconductor heterojunctions

•An ultrathin TiO2 layer was deposited on PCBM using a low temperature CVD process.•The TiO2 layer acts as a template for the functionalization of the PCBM surface with dipolar phosphonate SAMs.•The SAMs induce shifts in work function at the surface.•The SAMs induce shifts in energy level alignment between PCBM and α-NPD.

A general technique for modifying energy level alignment at organic–organic heterojunctions is introduced, and is demonstrated here for phenyl-C61-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.

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