Polycrystalline Si photovoltaic cells were coated with photoluminescent phosphors to increase the power conversion efficiency by down-conversion of high energy ultraviolet photons to less energetic visible photons, for which the Si solar cell conversion efficiency is greater. Phosphor coatings consisting of Y2O3:Eu3+, Y2O2S:Eu3+, 3,9-perylenedicarboxylic acid bis(2-methylpropyl) ester, and tetraphenylporphyrin dispersed in either polyvinyl alcohol or polymethylmethacrylate were tested. Cells coated with the Y2O3:Eu3+, or Y2O2S:Eu3+, showed an increased power conversion efficiency by up to a factor of 14 under UV illumination. The increased power conversion efficiency was shown to depend on the quantum efficiency of the down-conversion phosphor, the overlap between the photoluminescence excitation and the illumination spectra, and the overlap of the emission spectrum and the solar cell spectral response function. (c) 2007 American Vacuum Society.