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A3.07 - Infrared Plasmonic Absorption in Thin Crystalline Silicon Solar Cells 
April 22, 2014   3:45pm - 4:00pm

Poor internal reflection of IR light at the lossy metal rear reflector of crystalline silicon solar cells limits the spectral response of the cells near the silicon bandgap, even for highly reflective metals. Here, we present a thorough experimental and theoretical investigation of the optical properties of Si/dielectric/metal structures that are representative of the rear of rear-passivated crystalline silicon solar cells, and extend the analysis to “absorbing dielectrics” that represent the rear transparent conductive oxide (TCO) layer in silicon heterojunction solar cells. By calculating the electric field intensity at the surface of the metal, we find that for thin dielectric layers, p-polarized light arriving at the back surface above the Si/dielectric critical angle is strongly absorbed in plasmonic modes that cause significant internal reflection losses. We employ a ray tracer to calculate the total reflectance of a solar cell with random pyramids, using as input the internal reflectance values as a function of incident angle determined from the field intensities. The results reveal that—consistent with our measurements—dielectric layers at least 150 nm thick minimize absorption in the metal reflector; the rear passivation layers in solar cells can thus serve an optical as well as electrical role if properly designed. Finally, we demonstrate this in silicon heterojunction solar cells by measuring record IR internal quantum efficiency with a thick, low-refractive index dielectric buffer layer sandwiched between the rear of the cell and the metal reflector.

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Business Challenges to Starting a Materials-Based Company
Fred Kavli Distinguished Lectureship in Nanoscience
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