P-type and n-type conductivity refer to the conductivity characteristics of semiconductor materials. P-type semiconductor materials are positive charge carriers (hole-transporting) and n-type semiconductors are negative charge carriers (electron-transporting). The key element in semiconductor devices is the p-n junction. A p-n junction is formed when two regions of opposite conductivity type are adjacent to each other. P-N junctions have widespread use for many applications such as semiconductors, power semiconductors, field effect transistors (FETs), organic light-emitting diodes (OLEDs) and photovoltaic cells.
The usefulness of electrically conducting organic materials may be associated to a large extent with a combination of properties such as desirable electronic properties (e.g. low electrical resistivity), chemical stability, and physical and chemical properties that would permit the preparation of useful articles for manufacture. The first two properties mentioned above are shared by a number of inorganic materials well known in the art, such as metals (e.g. aluminum, silver and copper) or semiconductors (e.g. gallium and silicon). Devises comprised of inorganic materials typically are brittle and require demanding manufacturing processes which make it both difficult and expensive to fabricate large area displays. However, the wide chemical versatility of organic molecules gives the organic conductors a distinct advantage over inorganic materials to the extent that it is possible to introduce and modify physical and chemical properties such as solubility, melting point, etc. by relatively minor changes in the chemical structure of the organic molecules. In other words, organic conductors or semiconductors open the possibility for tailor-made electrically conducting materials with properties not found in inorganic substances. As such, there have been intensive research efforts in developing organic materials to be used as conductors or semiconductors for electronic device applications.