Electronic polarization at pentacene/polymer dielectric interfaces: Imaging surface potentials and contact potential differences as a function of substrate type, growth temperature, and pentacene microstructure

Interfaces between organic semiconductors and dielectrics may exhibit interfacial electronic polarization, which is equivalently quantified as a contact potential difference (CPD), an interface dipole, or a vacuum level shift. Here we report quantitative measurements by scanning Kelvin probe microscopy (SKPM) of surface potentials and CPDs across ultrathin (1-2 monolayer) crystalline islands of the benchmark semiconductor pentacene thermally deposited on a variety of polymer dielectrics (e.g., poly(methyl methacrylate), polystyrene). The CPDs between the pentacene islands and the polymer substrates are in the range of -10 to +50 mV, they depend strongly on the polymer type and deposition temperature, and the CPD magnitude is correlated with the dipole moment of the characteristic monomers. Surface potential variations within 2 monolayer (3 nm) thick pentacene islands are ∼15 mV and may be ascribed to microstructure (epitaxial) differences. Overall, the microscopy results reveal both strong variations in interfacial polarization and lateral electrostatic heterogeneity; these factors ultimately should affect the performance of these interfaces in devices.