Development of solution aggregation controlled novel conjugated polymers for organic solar cells and electrochromic device application

Abstract

Conjugated polymer are researched and applied to various organic electronics due to their distinct characteristics such as color tunability, solution processability, flexibility/stretchability. In particular, the accessible molecular structure modification, which is a unique feature of organic material, has been led rapid performance improvement of organic electronic devices for a short period. In general, strong aggregation behavior and following superior charge carrier mobility of conjugated polymers in organic solar cells are preferred. However, severe aggregation could reduce the solubility and induce excessive crystalline domains, thereby deteriorate mechanical properties. Therefore, in this dissertation, the disadvantages of highly efficient alternating copolymer polymers with low solubility and mechanical properties were solved by rationalized aggregation control. In the first study, a novel terpolymer containing ester thiophene was developed to solve the problems of low solubility of D18 and the use of toxic solvents. As the ester thiophene ratio was increased, the solubility of the polymer was improved, but the charge transfer property was decreased showing trade-off relationship. However, by optimizing the monomer ratio, we were able to develop non-toxic solvents processable high performance solar cell material. In the second study, in order to improve the mechanical properties of the PM6, a terpolymer, capable of distorting main chain was developed. Appropriate reduction of the planarity and rigidity of the main chain according to the monomer ratio not only improved the mechanical properties of the terpolymer itself, but also increased the compatibility with the electron acceptor material, enabling the development of high-performance solar cells with excellent mechanical properties. In the last study, we developed two novel dithienopyran-based conjugated polymers enclosing different hetero-atoms with distinct electronic characteristics to unveil the effect on electrochromic performance, especially for response speed. We found out electron donating alkoxy group in conjugated polymer accelerate bleaching speed of electrochromic device, whereas withdrawing alkylthio group promote coloration transition speed. We hope that these studies would serve as guidelines for the development of novel high-performance conjugated polymers.