Organic semiconductors with increased dielectric constants: properties and perspectives

Organic semiconductors are a versatile class of materials whose functionality can be tuned extensively with the use of synthetic organic chemistry techniques. Over the years, this has led to the development of organic light emitting diodes, organic solar cells, organic thermoelectric generators and organic field effect transistors, amongst other organic electronic devices. For organic photovoltaic (OPV) devices, a key challenge to developing high performance solar cells has been overcoming the exciton binding energy. The exciton binding energy keeps the photogenerated electrons (negative charge) and holes (positive charge) attracted to one another and hinders the generation of electrical current from the OPV device. Previous research has suggested that one way to tune the exciton binding energy in organic materials could be to change the dielectric constant. The dielectric constant is a material property that describes the ability of a material to screen charges from one another; in theory if the dielectric constant is increased, the exciton binding energy will decrease.

At the University of Groningen, various synthetic approaches have been employed to increase the dielectric constant of organic semiconductors. Of these approaches, the incorporation of polar ethylene glycol (EG) chains into the structure of known organic materials has shown particular promise. This thesis builds on this previous work with a focus on the fundamental aspects of how the EG chains affect the optoelectronic properties. In this way, the aim is to provide insight to the interplay between the dielectric constant and the functionality of organic semiconductors.