Charge transport in organic semiconductors

Abstract In this chapter, the basic principles of the origins of transport levels and bands, charge conduction in disordered materials, and injection from contacts are introduced. Charge transport in organics is fundamentally different than in inorganic semiconductors due to narrow transport bands that, in general, lead to charge transport via hopping, resulting in carrier mobilities that are at most only a few cm2/V s. Processes of charge injection leading to space charge limited transport that defines the current vs. voltage characteristics of the materials are discussed. Methods of measuring mobility, background charge densities, and quantifying charge recombination are described. Doping of organics using both molecular and atomic species to modify their conductivity is also considered. The theory of transport in energetically and structurally disordered films is developed. The chapter closes by describing, from first principles, the theory of conduction over organic and organic/inorganic semiconductor heterojunctions that are used in almost all organic photonic devices.