Nanoscale control of conjugated (conducting) polymers is especially important as the morphology of such functional materials plays a significant role in device performance, influencing properties such as conductivity, thermal stability, processability, and mechanical integrity. The goal of this proposal is to create new polymeric network materials for organic electronics devices, with improved performance due to the formation of well defined and continuous nanoscale conducting pathways. This goal will be achieved by combining the synthesis of near monodisperse conducting polymers (regioregular poly(3-alkylthiophenes) (rr-P3AT)s ), with the natural self assembly of block copolymers (BCPs) to create novel polymeric materials with the ability to form multiply continuous assemblies. There are two specific aims of this proposal. First, novel network forming ABC triblock copolymers containing an electrically conductive block will be synthesized. These materials will be designed such that they contain the block copolymer volume fractions necessary to generate the interfacial curvature and saddle surfaces, which are a hallmark of nanoscale networks. In addition, the chemical connectivity of the polymer will be designed such that crystallization of the conducting (rod) block is confined in order to maintain the network morphology. Next, membrane structures will be characterized by scattering, microscopy, and mechanical analysis techniques; membrane conductivity (and mobility) also will be examined using four point probe measurements, and dielectric spectroscopy. The proposed nanoscale network morphologies have superior mechanical attributes, relative to layers and cylindrical channels, and their percolating interconnected domains and large interfacial area present the opportunity to create conducting materials with tailored transport, chemical, and mechanical properties. These factors will lead to a dramatic improvement over polymer blend systems, where the creation of uniform-sized continuous pathways for conduction and transport is a key hurdle to improving the efficiency of polymeric devices.
Broader Impact:
The ability to create continuous nanoscale conducting pathways in organic thin films is crucial for further development and use of organic materials because poor electronic properties at domain boundaries often limit overall device properties. This is of particular concern for light emitting diodes (LEDs), thin-film transistors (TFTs), and photovoltaics (PVs), where improved transport is essential in the electronically active layers of these devices. While the synthesis of rr-P3AT BCPs has been reported in the literature, this work seeks to innovate their design. Specifically, the copolymers described above will contain one block that imparts toughness; a second block to provide confinement of the crystallizable block; and a third block that is crystallizable and conducting. A novel aspect of this work is that the chemistry of the conducting rr-P3AT block has been modified to lower the crystallization temperature, so that crystallization does not alter the overall self assembled block copolymer structure. The proposed research will provide new insights into the interplay between rod coil block copolymer composition, morphology and electronic properties. Collectively, this is expected to result in the optimization of CP morphology and electronic properties. Furthermore, this interdisciplinary project will train graduate and undergraduate students to address key scientific and engineering challenges in nanotechnology. Specific broader impact and educational initiatives are focused on increasing the participation of under represented groups. These include: providing summer research and mentorship opportunities through the PI's involvement with the ACS Diversity Partner Program and Minority Scholars Program. Additionally, the co-PI's involvement with several programs at Iowa State University [ISU] (AGEP, Freshman Honors, and NOBCChE) will be used to recruit graduate students from under represented groups to ISU. Finally, we propose the exchange of students between the University of Delaware, Chemical Engineering Department, and the ISU, Department of Chemistry, to broaden their research knowledge base.
Photovoltaic devices based on polymers possess several advantages over conventional inorganic semi-conducting materials, despite their lower overall efficiencies. These advantages include processing through low-cost and solution-based techniques, continuous versus batch fabrication, and electronic property manipulation through chemical synthesis that can lead to more versatile devices. The efforts in this proposal represent a transformative strategy for the design and investigation of nanostructured (1/1000th the width of a human hair) materials for organic solar cell applications. The long-term and potentially global impact of this research is that improved conducting copolymers will lead to the development of more efficient organic solar cells to reduce the costs and environmental impacts of energy generation. This effort will have substantial effects on the design of more efficient solar cells by establishing well-defined and potentially universal links between nanoscale architecture and charge transport, and by introducing a holistic approach to materials discovery linking molecular design, synthesis, detailed characterization, and property evaluation. Intellectual Merit: We examined several nanostructured polymer systems with tunable nanoscale morphologies to study the utility of controlled and well-defined small-scale structure on the transport behavior of polymeric materials for organic photovoltaics applications. We employed a series of specialized characterization tools to probe the assembly of the nanostructured polymers and linked the polymer behavior to macromolecular characteristics. These materials helped us gain new insights into methods to improve charge transport and to enhance the efficiency of organic photovoltaic devices. Key results were highlighted in multiple publications in the peer-reviewed literature, oral and poster presentations to the scientific and local community, and collaborative scientific activities with other academic research groups. Broader Impact: In addition to the design of new materials that can have a significant impact on the generation of clean energy and protect the environment, we engaged in a variety of educational and outreach activities that had a substantial and positive effect on the community. We partnered with the American Chemical Society (ACS) through ACS’s Project SEED program to provide summer research opportunities in our laboratories for local high school students from groups underrepresented in science and engineering. The majority of the students have chosen to continue their education at the college/university level. This activity has catalyzed several similar outreach programs across the University campus with a goal of broadening the pipeline of students who are engaged in furthering their educational opportunities and experiences. Additionally, the principal investigator of this project designed and taught a new nanoscale materials course and revitalized an introduction to polymer course that reached approximately 300 students during this project. These courses have provided relevant materials insights that have proven useful for students interested in pursuing both industrial and academic career opportunities.
