Organic Semiconductors: Purification and Crystal Growth

First, a brief overview is given on literature dealing with purification, purity assessment, and crystal growth methods which are applicable to organic photoconductors and semiconductors under the aspect of the required high purity. Then some recent examples are presented of purification, material handling and crystal growth of some selected compounds (perylene, naphthalene, phenanthrene, TTF:chloranil and bipyridylammonium: (TCNQ)2). Progress is reflected in greatly improved electrical properties of these materials which allowed detection of entirely new features, such as enhanced charge carrier scattering at phase transitions and non-Ohmic transport. Finally, some advanced crystal growth techniques are presented: Czochralski growth of organic molecular crystals under high purity conditions, flux growth of donor:acceptor crystals from a melt solution in one of the two components, oriented epitaxial growth “organic on organic” and epitaxial growth of organic materials on inorganic substrates.