Charge injection barrier at the pentacene thin film and electrode interface characterized by time-resolved electrostatic force microscopy

The contact resistances at the metal–organic interface often limit the performance of organic thin-film transistors. However, it is not straightforward to characterize the electrical property of the metal–organic interface of the organic thin film. This is because the conventional electrical measurement only gives the total electrical property of the metal–organic–metal system that is affected by many grain boundaries. In this study, we investigated a single pentacene grain connected to a Au electrode by time-resolved electrostatic force microscopy (tr-EFM), which can capture the time-evolving electrostatic force images at a nanometer-scale spatial resolution. Using the tr-EFM, we found the gradual and uniform potential increase in the pentacene grain following the positive step voltage applied to the Au electrode, which indicates that the resistance in the grain–electrode system is governed by the grain–electrode interfacial resistance. By assuming the equivalent circuit of the grain–electrode interface system, we reconstructed the femto-ampere-order current-to-voltage characteristic at the grain–electrode interface. The asymmetric characteristic in the hole injection regime and the ejection regime suggests the existence of a metal–organic Schottky junction at the interface.