Organic semiconductor
An organic semiconductor is an organic compound that exhibits similar properties to inorganic semiconductors. That is, hole and electron conduction and a band gap. Similar to inorganic semiconductors, organic semiconductors can be doped. Highly doped organic semiconductors, for example Polyaniline (Ormecon) and PEDOT:PSS, are also known as Organic metals.
As the origin of conductivity, two kinds of carriers are well known. One is a π-electrons and the other is unpaired electrons. Generally speaking, electronically neutral molecules gathered by Van der Waals force are composed of organic crystals. Therefore, almost all organic solids are insulators, which do not conduct electricity easily. However, in crystals that consist of molecules that have the π-conjugate system, electrons can move via π-electron cloud overlaps. That is why these crystals can conduct electricity. Polycyclic aromatic hydrocarbons and phthalocyanine salt crystals are examples of this type of organic semiconductor.
In some organic molecules, even unpaired electrons can stay stable for a long time. In such cases, unpaired electrons will be the carriers. This type of semiconductor is also obtained by pairing an electron donor molecule and an electron acceptor molecule and is called a charge-transfer complex.
The study of a charge-transfer complexes began with the discovery of the strikingly high conductivity of perylene-iodine complex (8 Ωcm) in 1954. In 1972, the TTF-TCNQ complex, whose conductivity is metallic, was synthesized. In 1980, superconductivity was observed in TMTSF-PF6 complex.
McGinness, Corry, and Proctor reported a high conductivity state in a polyacetylene (melanin) and the first organic electronic device. This was a voltage-controlled switch (Science, vol 183, 853-855 (1974)). Their orginal "gadget" is now in the Smithsonian's collection of early electronic devices.
See www.organicsemiconductors.com
Organic semiconductors are attractive as active elements in optoelectronic devices such as light emitting diodes (LED), solar cells and also field effect transistors (FET). There are many strong points of organic semiconductors, such as easy fabrication, mechanical flexibility, and low cost. Melanin is a semiconducting polymer currently of high interest to researchers in the field of organic electronics in both its organic and synthesized forms.
Both short chain (oligomers) and long chain (polymers) organic semiconductors are known. Typical examples for semiconducting oligomers are: Pentacene, Anthracene and Rubrene. Some semiconducting polymers are: Poly(3-Hexylthiophene), Poly(p-phenylvinylene) and F8BT.