In this International Collaboration in Chemistry between US Investigators and their Counterparts Abroad (ICC) project funded by the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division and the Office of International Science and Engineering, Michael Chabynic and Craig Hawker of the University of California at Santa Barbara will synthesize hole and electron transporting polymers that can be utilized in nanoimprint lithography to form layers for organic photovoltaic devices. The approach is to synthesize poly(alkyl selenophene)s and copolymers of poly(cyclopenta-dithiophene) with poly(benzothiadiazole) containing thermal and photo-crosslinkable side groups, and these donor polymers will be examined for use in nanoimprint lithography. Next, novel poly(benzotrithiophene) donor polymers and fused thiazole and selenazole acceptor polymers will be prepared and studied. Conformal parylene C coatings will be stacked onto the nanoimprinted donor polymer layer before the double imprint of the acceptor polymer is deposited. Additionally, non-crystalline dyes will be added to the donor layer that should migrate to the surface upon annealing of the donor layer in the imprinting process. These interfacial layers should help to reduce the kinetics of back electron transfer during the charge separation step. This work includes an international collaboration with Prof. Martin Heeney and Prof. Iain McCulloch of the Imperial College London, U.K. Profs. Heeney's and McCulloch's work will be funded by the Engineering and Physical Sciences Research Council (EPSRC). The broader impacts involve training graduate students and enhancing infrastructure for research and education through establishment of an international collaboration between universities in the U.S. and the U.K. The collaborators will endeavor to develop course materials on organic electronics that can be used in the curricula at both universities.
Organic polymer-based solar cells show great technological promise but have significant drawbacks in terms of low efficiencies and significant processing problems. This research will enhance our fundamental understanding about how organic polymers can be used to form solar cells and capture light and turn it into electrical energy. By exploring new types of polymers, this research could lead to easier to process and less expensive solar cell technologies.
Solar cells convert light from the sun into electricity providing a source of renewable energy. Most solar cells are made from highly purified silicon, which is expensive to produce. Silicon solar cells are also relatively fragile which increases their cost of installation. For these reasons, solar energy conversion is still costly compared to combustion of fossil fuels. If solar cells could be made from materials that are simpler to manufacture and are less fragile, then the cost of electricity generated from them would be more competitive. Organic polymers, plastics, can be synthesized at large scales and made into rugged, mechanically flexible solar cells. These materials can be printed from solvent, like an ink, allowing for scalable manufacture. Currently the performance of organic solar cells lags that of silicon solar cells therefore significant effort is required to improve their performance and to achieve their full potential. During this project, researchers in the U.S. have collaborated with researchers in the U.K. to develop new materials and processes to fabricate organic solar cells. International collaboration was critical to the success of this work. The research required need a combination of research expertise and allowed students to learn how to engage in a multinational research project. This collaborative effort led to significant research outcomes that improved the ability to process and control the performance of organic solar cells. One success of the project was the development of sugar-based additives to control the structural order in organic polymers during casting from solvent. The structural order in organic solar cells is known to be a critical factor in their power conversion efficiency. The researchers used simple, low cost-organic additives to direct the structural order in semiconducting polymers during coating processes. These additives helped to remove the reliance on empirically determined processing methods and now enhance the ability to form solar cells reproducibly. Another success of the project was the development of novel crosslinkable polymers that provide structural stability in organic solar cells. Cross-linking polymers increases their resistance to structural change at elevated temperatures. The development of crosslinkable polymers that can absorb light over a broad range of the solar spectrum in this project provides a means to make more durable organic solar cells. The research in the project was performed by graduate and undergraduate student researchers The students gained important training in advanced research methods and in working across intellectual disciplines. Female and African American students were involved in the research effort helping to increase the diversity of the scientific workforce. The students and their mentors also helped to broaden participation in science through science outreach activities to K-12 students.
