Determination of the Polaron Density in Chemically Doped Conjugated Polymers

Sammanfattning: Semiconductors have become indispensable in modern electronics, playing vital roles across diverse devices such as computers, mobile phones, and solar cells. While inorganic semiconductors, such as silicon, currently dominates the industry, organic semiconductors offer promising alternatives. One of the most widely studied classes of organic semiconductors is conjugated polymers. Chemical doping is a critical tool that allows to tune their electrical conductivity through the introduction of positive or negative charge carriers, i.e. polarons, by the addition of dopants. The ability to adjust the polaron density is essential, as devices that employ conjugated polymers operate within distinct ranges of charge-carrier concentration. Therefore, accurately measuring and quantifying the number of polarons is paramount for both material development and device engineering. This thesis explores methods for measuring the polaron density in the high doping regime. The results suggest that optical methods can be used to effectively estimate the polaron density in chemically doped conjugated polymers. The methodology is then used to demonstrate that chemical doping significantly effects the mechanical and rheological properties of conjugated polymers. Furthermore, it is found that the concept of double doping, which involves the transfer of two electrons between the polymer and the dopant molecule, is a generic concept that extends beyond quinodimethane-type dopants. The concepts elucidated in this thesis aid the development of an in-depth understanding of structure-property relationships relevant for doped conjugated polymers. Through addressing fundamental questions and establishing a foundation for future inquiry, this thesis contributes to the ongoing advancement of the dynamic field of organic electronics.