Enhancement of Performance of Crystalline and Amorphous Silicon Solar Cells through Optical Engineering by Nanostructured Materials

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Optical engineering of solar cells by nanostructured materials has recently emerged as a new frontier of photovoltaic research. Noble metal and dielectric nanostructures that can scatter and guide light have shown great capability for significantly improving the energy conversion efficiency of both crystalline and amorphous silicon solar cells, indicating a direction towards an innovative pathway for the advancement of solar industry. Silver nanoparticles applied on the front and rear surfaces of solar cells have dominated theoretical and experimental research as their high polarizability leads to large plasmonic scattering of the incident electromagnetic spectrum resulting in a reduction of reflectivity of the front surface as well as light trapping due to scattering. However, the joule loss of incident power in metal nanoparticles becomes very critical while designing high efficiency silicon solar cells. The use of lossless dielectric therefore emerges as an alternate solution to metal nanoparticles. Dielectric nanoparticle array helps to reduce the reflection losses by grading the refractive index mismatch in between silicon substrate and air along with omni-directionality. With a proper choice of design, photon transmission of more than 97 % of the incident photons in the solar AM 1.5 spectrum can be achieved which is comparable to the photon transmission by conventionally textured and ARC silicon surface. Further enhancements can be obtained by embedding lossless dielectric nanoparticles in the active absorber silicon layer to enhance scattering and corresponding light trapping. Optical simulations combined with the electrical model of a solar cell shows that a relative improvement in efficiency of about 6 % is obtained when 200 nm radius voids having 30 % coverage are embedded in a 20 μm thick solar cell to be pronounced in thinner cells (25 % for a thin cell 2 μm thick). For amorphous silicon solar cells also, optical engineering of the front glass surface by texturing and/or suitable coverage of silica nanoparticles have shown significant reduction in reflectivity and greater angular scattering of light leading to a large enhancement (about 6 %) in efficiency. The research work leading to possible performance enhancement in silicon solar cells through optical engineering by nanostructured will be discussed.