Optical Layers and Materials for Next Generation Solar Cells
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OPTICAL LAYERS AND MATERIALS FOR NEXT GENERATION SOLAR CELLS Ping Lee1, Jason Shank1, Komal Magsi1, Yeona Kang1, C.M. Fortmann1, 2 1. Materials Science and Engineering Department, Stony Brook University, Stony Brook, NY 11794-2275 2. Idalia Solar Technologies LLC, 270 Lafayette St. Suite 1402 New York, NY 10012 Abstract Layers that enhance light scattering and Raman-scattering-based spectral modification for solar cell applications were investigated. Titanium-oxide based rear diffuse reflector were found to increase the long wavelength response of crystalline solar cells. Also particle within the Titanium-oxide produce a far greater Stokes and anti-Stokes shift when compared to bulk crystal counterparts. The anti-Stokes to Stokes shift ratio in these particle systems is also greater and increased with increasing probe or bias light intensity. When applied to solar cells these layers extend the red response and thereby increase the overall performance. Introduction Over thirty years of solar cell advancement provides a vista to new strategic technologies for greater photovoltaic solar energy production. This work examines the increased performance and reduced cost made possible by front and rear mounted spectral modification layers for use with a variety of solar cell platforms [1]. Since, photovoltaic cells convert a narrow portion of the sun’s energy to electrical power any means that broadens the response without consuming useful light will lead to improved efficiency. Front mounted systems that down convert UV light and rear mounted systems that up convert light are sought. Raman up converters incorporated into the diffuse rear reflector offer a means by which to scavenge unused light and convert it into light of sufficient energy to broaden the conversion range. Raman scattering is an intrinsically weak phenomena commonly used for material characterization. The challenge is to increase the shift to levels that result in significant improvement of solar cell performance. On the other hand Raman scattering can account for significant loss (~~25%) in long distance fiber optic communication. Raman-scattering (Stokes and anti-Stokes shift) based up-conversion characterized by: energy and momentum conservation was investigated because it has no minimum photon flux requirement and when positioned at on the back of the solar cell minimal parasitic light absorption. Experiment Titanium oxide and Zirconium oxide/Titanium oxide mixed particles films of various thicknesses were prepared and applied to the back of commercial silicon solar cells (after removal of the as delivered rear contact paste). Similar films were also deposited onto
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glass slides using a standard hobby spray apparatus. To facilitate film spraying nanoparticles were mixed with isopropanol and water. The films were then annealed at 500 oC for one hour and slow cooled. Film coated glass slides were placed in front of the reference silicon solar cell (~ 16% efficient under AM 1.5 illumination) and the quantum efficiency measured using a Newport Oriel q
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