Organic Semiconductor

An organic semiconductor is an organic material with semiconductor properties. That is, with an electricalconductivity between that of insulators and that of metals. Single molecules, short chain (oligomers) and organicpolymers can be semiconductive. Semiconducting small molecules (aromatic hydrocarbons) include the polycyclic aromatic compounds pentacene, anthracene, and rubrene. Polymeric organic semiconductors include poly(3-hexylthiophene), poly(p-phenylene vinylene), as well as polyacetylene and its derivatives.

Typical current carriers in organic semiconductors are holes and electrons in π-bonds. Almost all organic solids are insulators. But when their constituent molecules have π-conjugate systems, electrons can move via π-electron cloud overlaps, especially by hopping, tunnelling and related mechanisms. Polycyclicaromatic hydrocarbons and phthalocyanine salt crystals are examples of this type of organic semiconductor.

Mainly due to low mobility, even unpaired electrons may be stable in charge-transfer complexes. Such unpaired electrons can function as current carriers. This type of semiconductor is also obtained by pairing an electron donor molecule with an electron acceptor molecule.

Notes from wikipedia:  http://en.wikipedia.org/wiki/Organic_semiconductor#Characterization