Band alignment at the organic-inorganic interface

The band alignment of the bithiophene interface with a diverse range of substrates has been determined by a combination of ultraviolet photoemission and work function measurements. Not only is vacuum level alignment clearly shown to be invalid but also any sort of linear relationship between band alignment and substrate work function is shown not to be the case. Rather, the alignment is determined by the interface dipole, which is specific to the interaction at the inorganic-organic interface. The interface dipoles, which always appear, while dominated by the first monolayer interaction, are completed after two to three monolayers. As the ionization potentials of the films are shown to be constant, it is argued that a simple work function measurement, for an organic film on a particular substrate, quantifies the band alignment.