It is expected that organic semiconductors based on low-molecular or polymer materials will also be used increasingly in the future in many fields of the electronics industry alongside conventional inorganic semiconductors. These materials afford many advantages compared to conventional inorganic semiconductors, for example an improved substrate compatibility and an improved processability of the semiconductor components based thereon. They allow processing on flexible substrates and make it possible to adapt their frontier orbital energies to the respective field of application using the methods of molecular modelling. “Organic electronics” focuses on the development of new materials and manufacturing processes for the production of electronic components based on organic semiconductor layers. Above all, these include organic light-emitting diodes (OLEDs), organic field-effect transistors (OFETs) and organic photovoltaics. A high development potential, for example in storage cells and integrated optoelectronic devices, is attributed to organic field-effect transistors. In organic light-emitting diodes (OLEDs) the property of materials is utilised to emit light when these materials are excited by electric current. In particular, OLEDs are an interesting alternative to cathode ray tubes and liquid crystal displays for the production of flat screens. Owing to the very compact construction and the intrinsically relatively low power consumption, devices which contain OLEDs are suitable in particular for mobile applications, for example for applications in mobile telephones, laptops, etc. A high development potential is also attributed to materials which have maximum transport distances and high mobilities for light-induced excited states (high exciton diffusion lengths) and are therefore advantageously adapted for use as an active material in organic solar cells, particularly in “excitonic solar cells”.
It is known to modify the electronic properties of silicon semiconductors by doping. An increase in conductivity is achieved by generation of charge carriers and, depending on the type of doping agent (dopants) used, the Fermi level of the semiconductor is modified.
It is further known that the electrical conductivity of organic semiconductors can also be influenced by doping. Organic semiconducting materials can be formed from compounds having good electron donor properties or good electron acceptor properties. Strong electron acceptors such as tetracyano quinone dimethane (TCNQ) or 2,3,5,6-tetrafluorotetracyano-1,4-benzene quinone methane (F4TCNQ) are known for doping electron donor materials. These produce “holes” in electron-donor-like base materials (hole transport materials) by electron transfer processes, the number and mobility of these holes changing the conductivity of the base material. For example, N,N′-perarylated benzidines, N′N′,N″-perarylated starburst compounds or specific metal phthalocyanines, such as zinc phthalocyanine (ZnPc) in particular, are known as materials having hole transport properties.
EP 1 596 445 A1 describes the use of quinine derivatives, which exhibit a lower volatility than tetrafluorotetracyano quinone dimethane (F4TCNQ) under identical evaporation conditions, for doping an organic semiconductor matrix material. In practice 1,4-quinone diimines substituted with fluorine and/or chlorine as well as 1,4,5,8-tetrahydro-1,4,5,8-tetrathia-2,3,6,7-tetracyano anthraquinone (CN4TTAQ) are used. Their tendency to migrate into adjacent undoped layers is a drawback, particularly with halogen-containing dopants. In addition, the service life of electronic components produced therefrom, and in particular of OLEDs could also be improved.
There is also a great need for new dopants for organic electronics having advantageous electronic and application-specific properties.