Organic Semiconductors - History

History

In 1862, Henry Letheby obtained a partly conductive material by anodic oxidation of aniline in sulfuric acid. The material was probably polyaniline. In the 1950s, researchers discovered that polycyclic aromatic compounds formed semi-conducting charge-transfer complex salts with halogens. In particular, high conductivity of 0.12 S/cm was reported in perylene-iodine complex in 1954. This finding indicated that organic compounds could carry current. In 1972, researchers found metallic conductivity in the charge-transfer complex TTF-TCNQ. Superconductivity in charge-transfer complexes was first reported in the Bechgaard salt (TMTSF)₂PF₆ in 1980.

Similar conductivity values in linear backbone polymers (in an iodine-"doped" and oxidized polypyrrole black) were reported in 1963. The 1964 monograph Organic Semiconductors cites multiple reports of similar high-conductivity oxidized polyacetylenes.

In 1974 John McGinness and coworkers reported a working organic polymer electronic device . These investigators reported a high conductivity "ON" state and hallmark negative differential resistance in melanin, an oxidized copolymer of polyacetylene, polypyrrole, and polyaniline. Melanin is a semiconducting polymer currently of high interest to researchers in the field of organic electronics in both its natural and synthesized forms. This device was a "proof of concept" for their earlier paper in 1972, outlining what is now the classic mechanism for electrical conduction in such materials. In a typical "active" device, a voltage or current controls electron flow. This device is now in the Smithsonian's collection (see figure). An alternative interpretation of their results is given in.

In 1977, Shirakawa et al. reported high conductivity in oxidized and iodine-doped polyacetylene. They received the 2000 Nobel prize in Chemistry for "The discovery and development of conductive polymers". Similarly, highly-conductive polypyrrole was rediscovered in 1979.

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 in biosensing applications. Organic semiconductors have many advantages, such as easy fabrication, mechanical flexibility, and low cost.