Performances Enhancement of Thin Si Film Photovoltaic (PV) Devices by incorporating Ag Nanoparticles (Ag NPs)

P. Yu, P.S. Pokam, T. Pingault, J-P. Blondeau, E. Ntsoenzok, C. Andreazza, J. Roussel, P. Dutheil, A-L. Thomann, A. Caillard, E. Mustapha, J. Meot, E. Millon, P. Andreazza
CNRS CEMHTI,
France

Keywords: Silver nanoparticles, plasmonics, solar cells, scattering

Summary:

Thin Si film solar cells offer the benefit of reducing material consumption and fabrication costs. Additional benefits include advantages of light-weight and possible flexible devices by roll-to-roll deposition processing. However, such thin absorbing layer reduces the photovoltaic efficiency, due to the decrease in layer optical path length. Metal NPs such as Ag can exhibit strong localized surface plasmon resonances (SPR) at UV, visible and NIR wavelengths. Their optical properties can be tuned by changing their size, shape, or by altering the local dielectric environment. They have been shown to increase the absorption in the active material and then the cell performances. However, NPs size and position in such cells need to be optimized. Our work’s goal is to understand NPs influence in such cells and to perform an optimal structure by increasing the light absorbed within the cell using NPs scattering and luminescence. Modeling based on Mie theory is first carried out with bhmie program using bulk Palik data. The SPR properties of an Ag sphere are calculated for various diameters and refractive medium indexes. Using simulation parameters, ultra-thin Ag layers were deposited on different substrates by Plasma sputtering magnetron or evaporation under different conditions. The individual quasi-spherical NPs were realized with diameters include from 20-110nm. UV-Visible spectroscopy displays localized SPR respectively for Ag layers on different substrates. SEM pictures give access to the particles size distribution and are injected as input data for Mie simulation results, Diffusion reflectance spectroscopy is used to compare initial substrate with NPs covered ones. Thin Si solar films cells with Ag NPs based on these results were prepared. Characterized with Spectral Response, the configuration in NIP junction with the Ag NPs in back contact optimizes the photovoltaic properties with a performance improvement about 14%-19%. It is almost the best improvement induced by NPs in such cells reported so far. This improvement observed at wavelength between 550~750nm is due to Ag NP backscattering. The research leading to these results has received funding from the European Union Seventh Framework Programme (FP7/2007-2013) under grant agreement n° 608593.