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Encyclopedia > Organic semiconductor

Semiconductors are compounds whose electrical conductivity is midway between that of typical metals and that of insulating compounds. 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-phenylene vinylene), F8BT, as well as polyaectylene and its derivatives. In chemistry, an oligomer consists of a finite number of monomer units (oligo is Greek for a few), in contrast to a polymer which, at least in principle, consists of an infinite number of monomers. ... A polymer is a long, repeating chain of atoms, formed through the linkage of many molecules called monomers. ... Pentacene is an aromatic molecule consisting of 5 fused benzene rings. ... In chemistry, anthracene is a solid polycyclic aromatic hydrocarbon consisting of three benzene rings derived from coal-tar. ... Rubrene (5,6,11,12-tetraphenylnaphthacene) is a polycyclic aromatic hydrocarbon. ... The monomer repeat unit of unsubstituted polythiophene. ... Poly(p-phenylene vinylene) (PPV) is conducting polymer of the rigid-rod polymer host family. ...


With significant overlap, there are roughly two major classes of organic semiconductors. These are 1) the organic charge-transfer complexes and 2) various derivatives of polyacetylene. The latter "linear backbone" polymers include polyacetylene itself, polypyrrole, and polyaniline. At least locally, the charge-transfer complexes often exhibit similar conduction mechanisms to inorganic semiconductors. This includes the presence of a hole and electron conduction layer and a band gap. As with inorganic amorphous semiconductors, tunneling, localized states, mobility gaps, and phonon-assisted hopping also contribute to conduction, particularly in the polyacetylenes. Like inorganic semiconductors, organic semiconductors can be doped. Highly doped organic semiconductors, for example Polyaniline (Ormecon) and PEDOT:PSS, are also known as organic metals. A charge transfer complex (CT complex) is defined as an electron donor–electron acceptor complex, characterized by electronic transition(s) to an excited state. ... Polyacetylene (PA) is conducting polymer of the rigid-rod polymer host family. ... A Polypyrrole (PPy) is a chemical compound formed from a number of connected pyrrole ring structures. ... Polyaniline (PANI) is a conducting polymer of the semi-flexible rod polymer family. ... A charge transfer complex (CT complex) is defined as an electron donor–electron acceptor complex, characterized by electronic transition(s) to an excited state. ... Inorganic chemistry is the branch of chemistry concerned with the properties and reactions of inorganic compounds. ... A semiconductor is a material that is an insulator at very low temperature, but which has a sizable electrical conductivity at room temperature. ... e- redirects here. ... This article or section does not adequately cite its references or sources. ... Normals modes of vibration progression through a crystal. ... In semiconductor production, doping refers to the process of intentionally introducing impurities into an intrinsic semiconductor in order to change its electrical properties. ... Polyaniline (PANI) is a conducting polymer of the semi-flexible rod polymer family. ...


Several kinds of carriers mediate conductivity in organic semiconductors. These includeπ-electrons and unpaired electrons. Almost all organic solids are insulators. However, when their constituent molecules have π-conjugate systems, electrons can move via π-electron cloud overlaps. Polycyclic aromatic hydrocarbons and phthalocyanine salt crystals are examples of this type of organic semiconductor. Electron atomic and molecular orbitals, showing a Pi-bond at the bottom right of the picture In chemistry, pi bonds (Ï€ bonds) are bonds with a single nodal plane containing the line segment between the two atoms. ... This article or section is in need of attention from an expert on the subject. ... A chemically conjugated system, is a system of atoms covalently bonded with alternating single and double bonds (e. ... Aromaticity is a chemical property in which a conjugated ring of unsaturated bonds, lone pairs, or empty orbitals exhibit a stabilization stronger than would be expected by the stabilization of conjugation alone. ... An aromatic hydrocarbon (abbreviated as AH) or arene [1] is a hydrocarbon, the molecular structure of which incorporates one or more planar sets of six carbon atoms that are connected by delocalised electrons numbering the same as if they consisted of alternating single and double covalent bonds. ... This article needs to be cleaned up to conform to a higher standard of quality. ...


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. A charge transfer complex (CT complex) is defined as an electron donor–electron acceptor complex, characterized by electronic transition(s) to an excited state. ...


History

Voltage-controlled switch, an "active" organic polymer electronic device from 1974. Now in the Smithsonian.
Voltage-controlled switch, an "active" organic polymer electronic device from 1974. Now in the Smithsonian.

For a history of the field, see: "An Overview of the First Half-Century of Molecular Electronics" by Noel S. Hush, Ann. N.Y. Acad. Sci. 1006: 1–20 (2003). Some key events: Image File history File linksMetadata Gadget128. ...


The study of conductive charge-transfer complexes began with the discovery of the strikingly high conductivity of perylene-iodine complex (8 Ωcm) in 1954. In 1972, researchers reported metallic conductivity in a TTF-TCNQ complex. In 1980, superconductivity was observed in TMTSF-PF6 complex. A charge transfer complex (CT complex) is defined as an electron donor–electron acceptor complex, characterized by electronic transition(s) to an excited state. ... Perylene or perilene is a polycyclic aromatic hydrocarbon with chemical formula C20H12 and CAS number 198-55-0, occurring as a brown solid. ... General Name, Symbol, Number iodine, I, 53 Chemical series halogens Group, Period, Block 17, 5, p Appearance violet-dark gray, lustrous Atomic mass 126. ... A complex is a whole that comprehends a number of parts, especially one with interconnected or mutually related parts. ... Year 1954 (MCMLIV) was a common year starting on Friday of the Gregorian calendar. ... 1972 (MCMLXXII) was a leap year starting on Saturday. ... A charge transfer complex (CT complex) is defined as an electron donor–electron acceptor complex, characterized by electronic transition(s) to an excited state. ... 1980 (MCMLXXX) was a leap year starting on Tuesday. ... A magnet levitating above a high-temperature superconductor (with boiling liquid nitrogen underneath), demonstrating the Meissner effect. ...


In 1963, Weiss et al reported [1] passive high conductivity in iodine-"doped" oxidized polypyrrole. While not generally acknowledged, this is the first report of modern highly-conductive polyacetylenes and related linear-backbone polymer "Blacks" or Melanins. They achieved a resistance of 1 ohm/cm. These authors similarly described the effects of iodine doping on conductivity, the conductivity type (n or p), and electron spin resonance studies on polypyrrole. In later papers, they achieved resistances as low as .03 ohm/cm [2][3], on the order of present-day efforts. Likewise, these authors noted an Australia patent application (5246/61, June 5, 1961) for conducting polypyrrole. Interestingly, highly-conductive Polypyrrole is often incorrectly reported as being discovered in 1979 by Diaz et al. J. Chem. Soc., Chem Comm, 1979: 635-6.[4]. A Polypyrrole (PPy) is a chemical compound formed from a number of connected pyrrole ring structures. ... Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ...


In a similar 1977 paper, Shirakawa et al reported [5] equivalent high conductivity in similarly oxidized and iodine-doped polyacetylene. The latter researchers received the 2000 Noble prize in Chemistry for " The discovery and development of conductive polymers " [6]. The Nobel committee made no reference to the Australian's earlier reports, which also were never cited by the Nobel winners. See Nobel Prize controversies. Since the first Nobel Prize was awarded in 1901, the proceedings, nominations and awardees have generated criticism and engendered much controversy. ...


Likewise, an organic electronic device was reported in a 1974 paper in Science [7]. Here, John McGinness and his coworkers reported a high conductivity "ON" state and hallmark negative differential resistance in DOPA Melanin, an oxidized copolymer of polyacetylene, polypyrrole, and polyaniline. This device was a "proof of concept" for an earlier paper in Science [8] outlining what is now the classic mechanism for electrical conduction in such materials, long considered part of the "development" cited in the 2000 Nobel award. In a typical "active" device, a voltage or current controls electron flow. This gadget is now in the Smithsonian's collection. John Edward McGinness, PhD, MD, Pioneer in Organic electronics and Nanotechnology. ... A VI curve with a negative differential resistance region Negative resistance or negative differential resistance (NDR) is a property of electrical circuit elements composed of certain materials in which, over certain voltage ranges, current is a decreasing function of voltage. ... Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ... Polyacetylene (PA) is conducting polymer of the rigid-rod polymer host family. ... A Polypyrrole (PPy) is a chemical compound formed from a number of connected pyrrole ring structures. ... Polyaniline (PANI) is a conducting polymer of the semi-flexible rod polymer family. ... The Smithsonian castle, as seen through the garden gate. ...


Analogous rigid-backbone organic semiconductors are now-used as active elements in optoelectronic devices such as organic light-emitting diodes (OLED), organic solar cells, organic field effect transistors (OFET), electrochemical transistors and recently also in biosensing applications. 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. Optoelectronics is the study and application of electronic devices that interact with light. ... An organic light-emitting diode (OLED) is a special type of light-emitting diode (LED) in which the emissive layer comprises a thin-film of certain organic compounds. ... An Organic Field-Effect Transistor (OFET) is a class of thin film transistors based on organic semiconductors. ... Broadly, melanin is any of the polyacetylene, polyaniline, and polypyrrole blacks and browns or their mixed copolymers. ... Organic electronics, or plastic electronics, is a branch of electronics that deals with conductive polymers, or plastics. ...


External Links

See also


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