This multidisciplinary symposium aims to bring together researchers working on quantifying nanoscale carrier transport processes in excitonic solar cells. Excitonic solar cells, including all-organic and dye-sensitized solar cells (DSCs), offer strong potential for inexpensive and large-area solar energy conversion. Unlike traditional inorganic semiconductor solar cells, where all the charge generation and collection processes are well understood, these excitonic solar cells contain extremely disordered structures with complex interfaces which results in large variations in nanoscale electronic properties and has a strong influence on carrier generation, transport, dissociation and collection. Rapid progress in this multidisciplinary area requires strong synergetic efforts among researchers from diverse backgrounds. Such effort can lead to novel methods for development of new materials with improved photon harvesting and interfacial treatments for improved carrier transport, process optimization to yield ordered nanoscale morphologies with well-defined electronic structures. The symposium plans to support the participation of underrepresented groups, including Hispanics, Native Americans, and women, through appropriate travel and registration support.

NON-TECHNICAL SUMMARY: Efficient and low-cost conversion of solar energy is important for environment protection and energy security of the nation. Excitonic solar cells offer strong potential for inexpensive and large-area solar energy conversion. These excitonic solar cells possess complex internal structure, which results in poor energy conversion efficiency. Rapid progress in this multidisciplinary area requires strong synergetic efforts among researchers from diverse backgrounds. This symposium aims to bring together scientists working on materials science, nanoscience, chemistry and theory to develop synergistic efforts to improve the efficiency of excitonic solar cells.

Project Report

Award No. DMR-1001266 Materials Research Society Symposium GG: Nanoscale Charge Transport in Excitonic Solar Cells 2010 MRS Spring Meeting, San Francisco, CA April 5 – 9, 2010 Symposium Organizers: Venkat Bommisetty, South Dakota State University Niyazi Serdar Sariciftci, Johannes Kepler University of Linz K.S. Narayan, Jawaharlal Nehru Centre Garry Rumbles, National Renewable Energy Laboratory Organic solar cells (OSC) have attracted worldwide attention from researchers due to their potential to replace traditional Si-based solar cells. Their low-cost and ability to be integrated with practically any surface (rooftops of bus stations to backpacks and umbrellas) makes OSCs an important technological path. Current SOC technologies produce cells with about 6-8% efficiency while commercialization of these technologies requires 10-13% efficiency. This symposium has brought together researchers developing novel materials, device technologies and approaches to study nanoscale charge transport processes that address current challenges to reach 10-13% efficiency. Two joint sessions with Symposium HH and II, namely, Molecular Engineering of OPV Materials and Advancing OPV, highlighted key recent developments in OPV. The symposium started with a tutorial session on Quantifying Nanoscale Charge Transport in Excitonic Solar Cells. Prof. Venkat Bommisetty, South Dakota State University, explained the importance of developing quantitative correlation between charge transport across nanoscale donor-acceptor morphologies and macroscale efficiency of the solar cell. He introduced scanning probe microscopy and the use of scanning probe based advanced characterization methods to probe these nanoscale processes. Prof. K.S. Narayan, JNCAR India, introduced concepts of OSCs; Prof. Andrey Kadashchuk, National Academy of Sciences of Ukraine, explained the effect of defects and disorder on charge transport and performance of OSCs. Prof. M.F. Baroughi, South Dakota State University, explained device concepts of OSCs and generalized charge transport models. Prof. Alan J. Heeger, UC-Santa Barbara, stressed the need to develop nanoscale morphologies that can efficiently collect a majority of charge carriers. During his talk on Recombination in Polymer Bulk Heterojunction Solar Cells, he described processes and materials that can lead to a cross-over from monomolecular recombination, which dominates at short circuit conditions, to bimolecular recombination that dominates at open circuit conditions. Using detailed experimental results, supported by theoretical simulations, Prof. Heeger concluded that monomolecular recombination is due to interfacial traps, whereas biomolecular recombination is due to band-to-band recombination. During the Charge Transport session, invited speakers (R.A. Street, PARC; Almantas Pivrikas, Linz Inst and Nir Tessler, Israel Inst of Technology) debated modeling and theoretical approaches that can explain nanoscale charge transport processes and their connection to macroscale efficiency of OSCs. The organizers are grateful for the National Science Foundation grant award that supported the travel of 12 students and early career researchers participating in the symposium. Proceedings published jointly with Symposia HH and II in both print and electronic formats (see MRS Online Proceedings Library at ) as Volume 1270 of the MRS Symposium Proceedings Series.

National Science Foundation (NSF)
Division of Materials Research (DMR)
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Linda Sapochak
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