The first example of systematic control of the work function of a conducting polymer is illustrated for PEDOT:PSS. A nanometer-thick film of TiO2 is formed on the PEDOT:PSS surface and forms an adhesion layer to bond phosphonic acids to the polymer; the work function of the PEDOT:PSS (ΦPEDOT:PSS) is adjusted by choice of phosphonic acid over a range of approximately 0.8 eV, and ΔΦPEDOT:PSS correlates strongly with the calculated gas-phase dipole moments of the phosphonates.Graphical abstractHighlights► A nanometer thick adhesion layer can be synthesized on the surface of a conducting polymer. ► Self-assembled monolayers of phosphonates can be formed on this adhesion layer. ► The dipole moments of the phosphonates can be manipulated to control the work function of the conducting polymer. ► Ultraviolet photoelectron spectroscopic analysis supports Kelvin probe measurements of work function changes.

•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.Graphical abstract