Energy level alignment at the organic-organic heterojunction interfaces: The role of gap states

Abstract

Understanding the mechanism of interfacial energy level alignment at various organic-organic heterojunctions is crucial for many technologically important organic electronic devices. Intensive research efforts have been devoted to the optimization of the electron energetics at these interfaces in order to improve the device performance. This thesis describes a balanced assessment on the understanding of the energy level alignment at the small-molecule based organic-organic interfaces, with particular emphasis on the role of gap states in organic thin films. Generalized pictures of gap states determined energy level alignment at the organic-organic heterojunctions are provided. The proposed gap states model helps to solve several critical issues in understanding the energy level alignment mechanism, such as the Fermi level pinning and band-bending like behaviors, showing a step towards the understanding of the interfacial energetics at weakly interacting organic heterojuntions.