Tailoring Transport in Transparent and Conducting Non-conjugated Polymers for Next-Generation Materials in Organic Photovoltaic Devices

Purdue University, West Lafayette IN

Investigators

Abstract

PI: Boudouris, Bryan Proposal Number: 1336731 Institution: Purdue University Title: Tailoring Transport in Transparent and Conducting Non-conjugated Polymers for Next-Generation Materials in Organic Photovoltaic Devices Organic photovoltaic (OPV) cells are recording device efficiencies that are beginning to rival many inorganic photovoltaic systems due to breakthroughs in the design of materials; as such, they present themselves as potential sources of sustainable energy generation. However, much of the groundbreaking research has focused on the design of pi-conjugated, light-absorbing macromolecules for use in the semiconducting layers of the OPV devices. Less success has been had in the realm of new polymeric materials for charge extraction at the electrode-organic interfaces of OPV devices despite the inherent need to remove the photogenerated charges from the solar cell efficiently. Therefore, there exists a critical need to develop and understand the fundamental charge transport in novel materials that are highly transparent, stable in ambient conditions, and that have the ability to transport charges in a rapid manner. Here, the PI introduces a promising new class of conducting polymers where a stable radical group is pendant on each repeat unit of a macromolecular chain whose polymer backbone is composed entirely of aliphatic carbon-carbon bonds; these materials are known as radical polymers. In addition to providing a method by which to conduct charge, radical polymers have the advantages traditionally associated with common aliphatic polymers (e.g., polystyrene) in that they: 1) can be generated from easily-synthesized monomers, 2) have their polymerizations occur through controlled mechanisms (e.g., controlled radical polymerizations) and on large scales, and 3) are processed readily either from solution or from the melt. Therefore, it is anticipated that the project will be able to generate transparent, conducting polymer thin films that have distinct synthetic, processing, and stability advantages over traditional OPV charge-collecting layers [e.g., poly(3,4-ethylene dioxythiophene)-poly(styrene sulfonate) (PEDOT:PSS)] while still retaining high charge transfer rates. The interplay between the molecular architectures of radical polymers and their solid state optoelectronic properties is important both in terms of fundamental structure-property relationships and for their performance in OPV devices. Deciphering these interactions will require a combination of polymer synthesis, structural characterization, and electronic testing. Implementation of these skills will result in: 1) the synthesis of new hole-conducting and electron-conducting non-conjugated polymers, 2) a description of charge transport in radical polymers such that improvement in the conductivity values of these functional macromolecules can occur, and 3) the utilization of these materials in OPV devices such that an environmentally-stable, low-cost alternative to existing charge collecting layers can be found. As such, completion of the research objectives will provide the fundamental scientific understanding to lay the foundation for a new area of polymer development and interfacial modifications in organic electronics with a deep impact in the organic photovoltaics and sustainable energy fields. This could lead to high-performance OPV devices that will help address current uncertainty in the global energy landscape. Furthermore, the basic discoveries regarding charge transport relationships in a new class of solid state polymeric conductors will have the potential to spread to other realms of organic electronics currently dominated by the conjugated materials. In addition to providing a concrete physical understanding of radical polymer conductors, this project will aid in the teaching and career development of graduate, undergraduate, and high school students through laboratory and outreach activities. For example, it will increase the participation of traditionally underrepresented groups in science and engineering through support of the Boudouris-founded Purdue Project SEED high school research experience. Bridging the disciplines of chemistry, polymer science, chemical engineering, and electrical engineering will afford the graduate, undergraduate, and high school students associated with this project a unique opportunity to engage in interdisciplinary, energy-related research that will have them well-prepared for future endeavors in academic and industrial circles. This synergistic relationship between research and educational activities will be of prime import in producing high impact scientific results, generating transformative technologies, and inspiring the next generation of sustainable energy scientists and engineers.