AmericanChemicalSociety.com

Summary: Affordable, renewable power generation, a critical component U.S energy independence, is not yet technologically or economically viable. New photovoltaic technologies, such as nanostructured organic photovoltaics (OPV), promise to greatly reducing both the manufacturing costs and the capital required to increase production capacity through low-temperature, solution-processing methods such as inkjet, spray and screen printing. However, chemical and morphological influences on device performance remain poorly understood, and development thus far has been largely empirical. Moreover, current OPV performance degrades to unacceptable levels after one year of operation, which is less than the required panel lifetime of 10 to 20 years. Fundamental studies that identify the origins of both high performance and degradation, and new developments to enhance both efficiency and extend lifetime, are critical to the success of this exciting new technology. This symposium focused on chemical and morphological influences on the efficiency and lifetime of organic photovoltaic cells.

Significance & Timeliness: Although the performance of organic photovoltaic technologies is nearing acceptable levels for commercialization, aging-induced performance degradation is considered to be the most significant single challenge to commercialization of the technology that has yet to be solved. Further improvements in cell efficiency remain critical to profitability and market acceptance. In 2008, several startups worldwide are beginning to manufacture OPV modules in small quantities, so now the Fall ACS 2009 meeting was the perfect time to address the aging issue from a fundamental science perspective.

Previous events: The theme was related to the International Summit on Organic Photovoltaic Stability (ISOS), sponsored by NREL of the DOE, that took place in Denver CO in July, 2008. While the emphasis of the ISOS was OPV manufacturing and testing standards, the ACS symposium provided a fundamental science counterpoint to discuss the origins of performance degradation and new, novel means to extend OPV device lifetime.

Factors contributing to accessibility: The community developing OPV technology for commercialization is decidedly international, with a variety of organizations distributed across the U.S., the U.K., and continental Europe. The European community is especially active. PRF funding substantially facilitated access to the conference for key European speakers working directly on these challenges in OPV technology development.

Program: The two-day symposium consisted of presentation from leading scientists in the OPV research community including Gilles Dennler from OPV startup Konarka, Martin Heeney from Queen Mary College of London, Alex Jen from University of Washington, Shijun Jia from OPV startup Plextronics, Tomaz Kowalewski from Carnegie Mellon University, Frederick Krebs from Riso National Laboratory in Denmark, Joachim Loos from Eindhoven University in the Netherlands, Michael McGehee from Stanford University, Adam Moule from University of California Davis, Thuc-Quyen Nguyen from University of California Santa Barbara, Garry Rumbles from the National Renewable Energy Laboratory, Yang Yang from University of California Los Angeles, and Luping Yu from University of Chicago. The program also included contributed presentations from a number of graduate students and postdoctoral researchers from around the globe. The ACS-PRF grant allowed Dr. Frederick Krebs, Prof. Joachim Loos, and Prof. Martin Heeney to attend the conference and present their work to the ACS community. Dr. Krebs presented on his work at Riso National Laboratory where they have developed roll-to-roll fabrication of solar cells on flexible substrates and are conducting detailed degradation studies. They have obtained promising results and showed demo cells that have been developed for powering portable LED lights for poor countries. Prof. Joachim Loos presented on work at Eindhoven University highlighting their characterization of the three-dimensional nanoscale organization of bulk heterojunction solar cells using tomographic transmission electron microscopy. Prof. Loos showed impressive images of how the three-dimensional nanostructure changes with various processing conditions. Prof. Martin Heeney presented on work at Queen Mary University highlighting the synthetic development of new semiconducting polymers for photovoltaics with lower band gaps to increase the device efficiency. Prof. Heeney replaced the sulfur in thiophene-based polymers with a selenium atom and showed how the inclusion of the selenophene rings lowered the band gap of the polymers. Overall, the symposium covered a broad spectrum of science relevant to organic photovoltaics including both the university and the industrial viewpoints and provided guidelines for future work that will potential result in both high efficiencies and high lifetimes for OPV devices.