Exciton

An exciton is a bound state of an excited electron and the hole it leaves behind in a material. It carries energy and can move through the material without transporting net electric charge.

Electron–hole pair: A semiconductor excitation consisting of an electron promoted to a higher-energy state and the vacancy it leaves behind. Their attraction binds the pair into an exciton.
Valence band: The range of electron energies occupied by electrons in a solid at low temperature. The hole usually marks a missing electron in this band.
Wannier–Mott exciton: A weakly bound exciton whose electron and hole are spread across many unit cells of a crystal. This extended form commonly describes excitons in conventional semiconductors.
Organic solar cell: A photovoltaic device that uses organic semiconductors to absorb light and generate electrical power. Its operation depends on exciton diffusion and separation at donor–acceptor interfaces.
Free electron–hole pair: An electron and hole in a material that are not bound together as a single state. Unlike an exciton, this pair is not held together by Coulomb attraction.
Coulomb interaction: The electrostatic interaction between electrically charged particles. It binds the negatively charged electron to the positively charged hole.
Conduction band: The range of electron energies in a solid where electrons can move through the material. Light can promote an electron here, leaving a hole behind.
Frenkel exciton: A tightly bound exciton localized mainly on one molecule or unit cell. Its compact structure is typical of molecular crystals and many organic materials.
Light-emitting diode: A semiconductor device that emits light when electrical current causes electrons and holes to recombine. Radiative exciton formation and decay can produce its emitted light.
Trion: A charged quasiparticle consisting of an exciton bound to an additional electron or hole. Its extra carrier gives it net charge, unlike a neutral exciton.

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