CAREER: Structure-Function-Property Relationships in Charged Conjugated Polymers

University Of California-Santa Barbara, Santa Barbara CA

Investigators

Abstract

Technical This CAREER project aims to understand the structure-function-property relationships in charged conjugated polymers for applications in plastic electronics. Conjugated polymers (CPs) are materials that have the optical and electrical properties of semiconductors with the mechanical properties of plastics. The project focus is on fundamental understanding of the optical and electronic properties of cationic and anionic conjugated polymers (conjugated polyelectrolytes) as a function of molecular structure, charge density (number of charge per repeat unit), type of counter ions, and material processing conditions. The advantage of conjugated polymers containing electrically charged functional groups is that they offer fine control of the polymer conformation in solution, and hence, the degree of electronic interaction of polymer chains in films (interchain interactions). These interchain interactions strongly influence optical and electronic properties and degradation rate such as photoluminescence quantum yield and lifetime, energy migration, and charge mobility in CP-based devices such as biosensors, light-emitting diodes (LEDs), solar cells, and field effect transistors (FETs), and so, the device efficiencies and operational lifetime. The approach is to control polymer conformation in solution by changing solvent, concentration, salt, functional group, charge density, and conjugated polymer backbone and film morphology by polymer conformation, annealing process, and various film fabrication methods. Light-scattering, steady-state and time-resolved spectroscopies, scanning probe techniques (Atomic Force Microscopy, Electrostatic Force Microscopy, and Conducting Atomic Force Microscopy), along with prototype device evaluation will be used to obtain a comprehensive understanding of polymer conformation, film morphology, optical and electronic properties, and charge transport at the nanoscale, and in bulk as a function of molecular structure and processing conditions. Specific goals include: 1) To understand and control charged conjugated polymer conformation in solution via molecular structure and processing conditions and how change in polymer conformation affects its photophysics. 2) To understand and control polymer photophysics and charge transport properties of polymer films as a function of molecular structure, charge density (number of charge per repeat unit), type of counter ions, and processing conditions. Non-Technical The broader impact of the project will be the link established between research and education at UCSB and the Santa Barbara community. Graduate and undergraduate students will be essential to carrying out the research. The research plan promotes teaching, training, and learning of graduate and undergraduate students in the field of organic semiconductors. The research is highly interdisciplinary; students will be exposed to a wide range of research experience in material design and synthesis, materials characterization, and device fabrication and evaluation that will provide breadth and flexibility for their future careers. They will develop knowledge in chemistry, physics, and materials science. Several graduate and undergraduate courses will be developed by the PI to strengthen and update new science in the science curriculum at UCSB. Through several outreach programs at UCSB, the PI will bring summer undergraduate students, college students, and high school teachers to her laboratory to participate in research activities. To increase the diversity and to promote children to go to college and major in science, the PI will participate in Science and Technology Day, an annual event that brings students and teachers from middle and high schools to UCSB to participate in science workshops and competitions.