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Nanophotonics and Plasmonics |
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Recent progress in the field of nanophotonic structures that enables one to couple optical fields with plasmonic excitations in metals opens up possibilities for a wide range of new applications. Over the years, our group has established capabilities to simulate nanophotonic structures fabricated out of metals and dielectrics, including finite difference in time domain (FDTD) methods and finite element simulation methods. We explore novel ways these plasmonic elements can be used to enhance optical functionalities at the system level. Our first application is the consideration of improving the power conversion efficiencies in organic solar cells. Achieving high power conversion efficiency in solar cells is fundamentally restricted by the fact that the solar energy reaches the surface of the earth as a broadband source, and all the photovoltaic devices we have has a fixed open-circuit voltage given by the material parameters of the device. Tandem cell architectures can resolve this issue, as multiple cells converting different portion of the solar spectrum are connected in series to achieve higher power conversion efficiency. For a wide-area solar cell systems, one must explore low cost fabrication techniques that can be scaled to a very large area devices. Organic solar cells provide a compelling solution in this regard, but they are constrained by short exciton diffusion length. Multi-junction vertical tandem cell is difficult to realize in organic materials due to the complex requirements on optical transparency and electrical transport. We proposed and analyzed a systems approach to organic solar cells that addresses many of the practical challenges. In our architecture (shown in figure below), the incoming solar energy is spectrally “pre-sorted” in the optical domain and matching organic devices are positioned in the appropriate image plane. This architecture enables natural implementation of tandem cells in lateral configuration. Furthermore, metallic optical cavities can be fabricated around each spectral region in a way that the cavity is resonant with the incident photon at that location, enhancing the optical absorption by think organic materials without sacrificing the diffusion characteristics of the photo-generated excitons. Using this approach, we estimate a dramatic improvement over conventional organic solar cell performance, enhancing the power conversion efficiency by as much as a factor of three. |
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Architecture for a lateral tandem configuration for an organic solar cell. |
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· Changsoon Kim · Jihnyun Cho |
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Project Participants: |
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· Air Force Office of Scientific Research · Defense Advanced Research Projects Agency · National Institute of Health (through Duke Center for Systems Biology) |
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Project Sponsor: |
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· Prof. David J. Brady, ECE, Duke University · Prof. Jie Liu, Chemistry, Duke University · Prof. Lingchong You, BME, Duke University · Dr. Scott McCain, Applied Quantum Technologies, Inc. |
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Project Collaborators: |
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Other applications of the plasmonic structures include substrates for surface-enhanced Raman spectroscopy (SERS) system and frequency-selective surfaces for spectral filters. In collaboration with Prof. Jie Liu in Chemistry and Prof. Lingchong You in Biomedical Engineering Department, we are exploring the fabrication of optimized SERS substrates for biomolecular sensing. We are also exploring periodic plasmonic structures to create spectral filters for multi-spectral imaging in the long-wave infrared spectral range. This work is performed in collaboration with Prof. David Brady’s group at Duke University. |
