In order to improve conversion efficiency of crystalline silicon solar cells, optically down-converting encapsulate films were prepared by introducing rare earth particles Y 2 SiO 5 : Ce 3þ , Yb 3þ into ethylene vinyl acetate. First, ethylene vinyl acetate and the filler particles (up to 5 wt%) were melt compounded. Then, 0.4-mm thick film samples were made from the compounds with a laminator. Light conversion properties of the ethylene vinyl acetate films were investigated by UV-Vis-NIR spectra and fluorescence spectra. The relationships between the light conversion and the film transmittance were analyzed. The results show that the Y 2 SiO 5 : Ce 3þ , Yb 3þ-filled films were able to optically down-convert the 457 nm blue-violet light to the 980 nm near-infrared light. Peel strength increased to 31% (from 14.2 N/mm