Organic electronics

Organic electronics is a field of materials science concerning the design, synthesis, characterization, and application of organic molecules or polymers that show desirable electronic properties such as conductivity. Unlike conventional inorganic conductors and semiconductors, organic electronic materials are constructed from organic (carbon-based) molecules or polymers using synthetic strategies developed in the context of organic chemistry and polymer chemistry. One of the promised benefits of organic electronics is their potential low cost compared to traditional electronics. The polymeric conductors have attractive properties, which include electrical conductivity (which can be varied by the concentrations of dopants) and comparatively high mechanical flexibility. The challenges in implementing of organic electronic materials are their inferior thermal stability, high cost, and diverse fabrication issues.

History

Electrically conductive polymers Traditional conductive materials are inorganic, especially metals such as copper and aluminum as well as many alloys. In 1862 Henry Letheby described polyaniline, which was subsequently shown to be electrically conductive. Work on other polymeric organic materials began in earnest in the 1960s. For example in 1963, a derivative of tetraiodopyrrole was shown to exhibit conductivity of 1 S/cm (S = Siemens). In 1977, it was discovered that oxidation enhanced the conductivity of polyacetylene. The 2000 Nobel Prize in Chemistry was awarded to Alan J. Heeger, Alan G. MacDiarmid, and Hideki Shirakawa jointly for their work on polyacetylene and related conductive polymers. Many families of electrically conducting polymers have been identified including polythiophene, polyphenylene sulfide, and others. J.E. Lilienfeld first proposed the field-effect transistor in 1930, but the first OFET was not reported until 1987, when Koezuka et al. constructed one using Polythiophene which shows extremely high conductivity. Other conductive polymers have been shown to act as semiconductors, and newly synthesized and characterized compounds are reported weekly in prominent research journals. Many review articles exist documenting the development of these materials. In 1987, the first organic diode was produced at Eastman Kodak by Ching W. Tang and Steven Van Slyke.

Electrically conductive charge transfer salts In the 1950s, organic molecules were shown to exhibit electrical conductivity. Specifically, the organic compound pyrene was shown to form semiconducting charge-transfer complex salts with halogens. In 1972, researchers found metallic conductivity (conductivity comparable to a metal) in the charge-transfer complex TTF-TCNQ.

Light and electrical conductivity André Bernanose was the first person to observe electroluminescence in organic materials. Ching W. Tang and Steven Van Slyke, reported fabrication of the first practical OLED device in 1987. The OLED device incorporated a double-layer structure motif composed of copper phthalocyanine and a derivative of perylenetetracarboxylic dianhydride. In 1990, a polymer light emitting diodes was demonstrated by Bradley, Burroughes, Friend. Moving from molecular to macromolecular materials solved the problems previously encountered with the long-term stability of the organic films and made high-quality films easy to produce. In the late 1990's, highly efficient electroluminescent dopants were shown to dramatically increase the light-emitting efficiency of OLEDs These results suggested that electroluminescent materials could displace traditional hot-filament lighting. Subsequent research developed multilayer polymers and the new field of plastic electronics and organic light-emitting diodes (OLED) research and device production grew rapidly.

Conductive organic materials

Organic conductive materials can be grouped into two main classes: polymers and conductive molecular solids and salts. Polycyclic aromatic compounds such as pentacene and rubrene often form semiconducting materials when partially oxidized. Conductive polymers are often typically intrinsically conductive or at least semiconductors. They sometimes show mechanical properties comparable to those of conventional organic polymers. Both organic synthesis and advanced dispersion techniques can be used to tune the electrical properties of conductive polymers, unlike typical inorganic conductors. Well-studied class of conductive polymers include polyacetylene, polypyrrole, polythiophenes, and polyaniline. Poly(p-phenylene vinylene) and its derivatives are electroluminescent semiconducting polymers. Poly(3-alkythiophenes) have been incorporated into prototypes of solar cells and transistors.

Organic light-emitting diode

An OLED (organic light-emitting diode) consists of a thin film of organic material that emits light under stimulation by an electric current. A typical OLED consists of an anode, a cathode, OLED organic material and a conductive layer.

OLED organic materials can be divided into two major families: small-molecule-based and polymer-based. Small molecule OLEDs (SM-OLEDs) include tris(8-hydroxyquinolinato)aluminium fluorescent and phosphorescent dyes, and conjugated dendrimers. Fluorescent dyes can be selected according to the desired range of emission wavelengths; compounds like perylene and rubrene are often used. Devices based on small molecules are usually fabricated by thermal evaporation under vacuum. While this method enables the formation of well-controlled homogeneous film; is hampered by high cost and limited scalability. Polymer light-emitting diodes (PLEDs) are generally more efficient than SM-OLEDs. Common polymers used in PLEDs include derivatives of poly(p-phenylene vinylene) and polyfluorene. The emitted color is determined by the structure of the polymer. Compared to thermal evaporation, solution-based methods are more suited to creating films with large dimensions.

Organic field-effect transistor

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