chargetransport

Charge transport refers to the movement of electric charge within a material or across interfaces. It may involve electrons and holes in electronic conductors and semiconductors or ions in electrolytes and solid ionic conductors. The principal descriptors are mobility (how quickly a charge carrier moves in a field), conductivity (how readily a material conducts charge), and diffusion (movement due to concentration gradients).

In metals and crystalline semiconductors, electronic transport occurs mainly via band conduction, where delocalized states allow carriers to respond to electric fields, and, in disordered or organic materials, by hopping between localized states. Ionic transport occurs when ions migrate through a lattice or solvent, often by hopping between energetically favorable sites and assisted by defects or solvent reorganization. Some materials are mixed conductors, supporting both electronic and ionic transport.

Models include the drift-diffusion framework for carriers under fields, band theory for delocalized electrons, and hopping models for localized states. In electron transfer processes, Marcus theory describes rates of charge transfer between redox sites. The Nernst-Einstein relation links diffusion and mobility in certain regimes, while percolation theory explains transport in disordered networks.

Charge transport is strongly influenced by interfaces, where energy-level alignment and contact resistances affect injection and extraction. This is central to devices such as batteries, fuel cells, solar cells, and sensors, and to biological systems where membrane potentials drive ion movement.

Typical metrics include mobility (μ), conductivity (σ), diffusion coefficient (D), and ionic transference numbers in electrolytes. Temperature, doping, crystal structure, and disorder govern transport behavior, often producing Arrhenius-type or variable-range hopping temperature dependences.