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Broad Band, High Efficiency Solar Cells


OBJECTIVE: Demonstrate a high-efficiency solar cell with a photovoltaic efficiency comparable to that of present day multi-junction solar cells but with a spectral response extending into the IR, suitable for autonomous vehicle or space platform applications. DESCRIPTION: Solar cell technology represents a key power management component in a variety of terrestrial and space based Air Force systems. Improvements in solar cell efficiency, as well as the ability to harvest solar energy over a broader wavelength range represents a means to significantly improve mission lifetime and effectiveness while still adhering to strict size and weight requirements. Recent advances in the development of nanomaterials with tunable intermediate bands and enhanced multi-exciton generation, as well as achievements in nanophotonics, hold significant promise for dramatic improvements in the photovoltaic efficiency of next generation solar cells [1,2]. Modern nanomaterials offer the possibility of improving the harvesting of solar radiation by including the IR region of the solar spectrum, as well as the ability to manage photoelectron kinetics for more effective photovoltaic conversion. In practice, however, the actual demonstration of a nanomaterial-based solar cell with conversion efficiency comparable to that of a state-of-the-art multi-junction solar cell, (30%-40%), has yet to be demonstrated. The intent of this solicitation is to prove, that through the integration of the theoretical and experimental aspects of nanomaterial research, nanophotonics, and photovoltaics, an efficient, broad band (all-weather), lightweight, reliable solar cell can result with performance characteristics exceeding that of present day multi-junction solar cells. By implicitly incorporating energy harvesting from the IR region of the solar spectrum, a low-visible light, all weather capability will result significantly impacting autonomous vehicle effectiveness and dramatically improving space platform power management efficiency. The photovoltaic device proposed is expected to incorporate the developing nanomaterials and advanced nanophotonic and photovoltaic technologies. The intent of this integration is to significantly increase the wavelength range over which energy harvesting occurs, increase the overall photovoltaic conversion efficiency and to reduce the both the thermal and recombination losses for improved photovoltaic conversion efficiency while still maintaining acceptable photovoltaic circuit characteristics. The resulting device will represent a significant advancement in next generation single-junction solar cell technology in terms of size, weight and conversion efficiency. By achieving efficiencies comparable to multi-junction technologies in a single-junction format a relatively inexpensive solar cell will result when compared to existing high-efficiency, energy harvesting components. PHASE I: Develop a solar cell device incorporating novel nanomaterials and advanced photovoltaic technologies. These efforts should include modeling, experimental demonstrations, and a detailed evaluation of the performance. The Phase I device should demonstrate at least 25% photovoltaic efficiency at AM 1.5 with a clear path towards improvements needed to reach the Phase II performance characteristics. PHASE II: Demonstrate a light-weight photovoltaic device with at least 30% efficiency at AM 1.5. Demonstrate all-weather operation due to effective harvesting and conversion of IR radiation. Propose a manufacturing scheme for the large, wafer scale, production of the device and address manufacturing costs compared to other multi-junction solar cell technologies in terms of cost per kg. PHASE III: Terrestrial and space based energy harvesting for remote and autonomous vehicles. Energy harvesting, power production, photovoltaics. REFERENCES: 1. A. Luque and A. Marti,"Increasing the Efficiency of Ideal Solar Cells by Photon Induced Transitions at Intermediate Levels"Phys. Rev. Lett., 78, 5014 (1997). 2. K. A. Sablon, J. W. Little,V. Mitin, A. Sergeev, N. Vagidov, and K. Reinhardt,"Strong Enhancement of Solar Cell Efficiency Due to Quantum Dots with Built-In Charge", Nano Letters, 11, 2311 (2011).
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