SOLAR: Integrated Electro-Photonic Development of Polymer Solar Cells

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TECHNICAL SUMMARY:This award on solar energy research is co-funded by the Divisions of Chemistry, Materials Research, and Mathematical Sciences of the Directorate for Mathematical and Physical Sciences. A collaboration of chemistry, physics, and applied mathematics groups at the University of North Carolina will explore the limitations of bulk-heterojunction polymer solar cells, which have been identified as economical and easy to manufacture. An interdisciplinary team will design, fabricate, and optimize photonic crystal solar cells that specifically address the disparate length scales in polymer photovoltaic materials, thereby confronting the major challenge in solar cell technology: efficiency. The aim is to achieve simultaneously an efficient absorption of photons with effective carrier extraction, but unfortunately the two processes have opposing requirements. Efficient absorption of light calls for thicker modules whereas carrier transport always benefits from thinner ones, and this dichotomy is at the heart of an efficiency/cost conundrum that has kept solar energy expensive relative to fossil fuels. The UNC approach, based on the advanced optical control possible with photonic crystals, enables efficient light capture by a photonic arrangement of nanostructures while significantly reducing the effective path carriers need to travel to reach contacts. Integrating an applied mathematics component into the team will enable rigorous and simultaneous optimization of both photonic crystal designs and carrier extraction pathways. Moreover, the optimized nanostructures will be scalable to large areal dimensions via a technique called PRINT (Pattern Replication In Nonwetting Templates), a recent breakthrough in roll-to-roll nanomolding pioneered in Chapel Hill. NONTECHNICAL SUMMARY:Polymer solar cells have demonstrable advantages such as ease and economy of fabrication, but to compete with the lower cost of fossil fuels they must attain higher efficiencies. A collaborative group of researchers at the University of North Carolina at Chapel Hill will use an interdisciplinary approach to optimize a novel type of photonic-crystal solar cell. Inspired by nature's own design, a design manifested in the beautiful iridescent colors of minerals, gems, insects, and butterflies photonic crystals enhance the absorption of light and are expected to increase solar cell efficiency. The unorthodox alliance of three disciplines at UNC (applied mathematics, chemistry and physics) will leverage rigorous mathematical modeling to optimize the design and fabrication of photonic crystal solar cells. Moreover, this atypical conjunction of a mathematician, a chemist and a physicist working together on the challenging problem of polymer solar cell efficiency will provide a unique educational environment for undergraduate and graduate students, one wherein the power of a diversity of backgrounds is emphasized in approaches to complex, interdisciplinary problems.