Theory of Optical Properties of Organic Semiconductors

Organic semiconductors consist of organic molecules, which are usually hydrocarbons. A hydrocarbon molecule usually consists of hydrogen and carbon atoms bonding, sometimes with other atoms of oxygen and nitrogen, depending on the structures. Organic solids are formed by the weak Van der Waals forces, leading to frail bonding caused by the weak overlap of the electronic wave functions between neighbouring molecules. The energy gap may be controlled by the degree of conjugation of the individual systems, which opens various possibilities for the modification of opto-electronic properties of organic semiconductors. The chapter describes a theoretical study of the optical properties of organic semiconductors is reviewed with a view to its application in devices such as organic solar cells and organic light-emitting devices (OLEDs). The invention of OLEDs, based on thermally activated delayed fluorescence, has become a very active field of research in organic electronics.