Characterization of Interfaces between Contacts and Active Layer in Organic Photovoltaics Using Impedance Spectroscopy and Equivalent Circuit Model

This study investigates the interface between the active layer and contacts in organic photovoltaics (OPVs) since the contact materials strongly affect the energy barrier at the interfaces. The interfacial characteristics are simply defined as a resistance-capacitance (R-C) shunt pair and extracted by fitting the impedance spectra to the equivalent circuit model. A change in the energy barrier is found to affect the values of R and C at the interface and the carrier transition time. In addition, the effect of electron buffer layer (TiO₂) thickness on the interfacial characteristics is analyzed using an impedance spectroscopy. The interfacial area between the hole buffer layer (MoO₃), and the active layer affects the values of R and C at the interface.