Enhancing The Performance Of Solar Cells By SrAl₂O₄:Eu²⁺,Dy³⁺ Phosphor

In this study SrAl₂O₄:Eu²⁺, Dy³⁺powders were synthesized via chemicalco-precipitation followed by hydrothermal treatment at200oC, which wereused as down-converting phosphors（DC）. DC films were made by tape castingprocess after forming a suspension of SrAl₂O₄:Eu²⁺, Dy³⁺powders in PVDF orPMMA in order to measure transmittance of films. The effective of films,thickness, and the phosphor content on the transmittance were discussed. Andthe photoelectric conversion efficiency was observed by coating films on solarcells using screen-printing technique.（1） SrAl₂O₄:Eu²⁺, Dy3+precursors were prepared according to thestoichiometric ratio n（Sr）:n（Al）:n（Eu）:n（Dy）=2:7:0.02:0.04by co-precipitation.After hydrothermal treating at200, the precursors were washed, filtered anddried, then calcined in weak reducing atmosphere. SEM showed powders werespherical primarily, and their sizes were from40to300nm. Fluorescencespectroscopy indicated that the powder could be excited by250⁴50nmultraviolet light, and emitted510nm visible light. These experiments indicatedthat the phosphors were suitable for making down conversion materials.（2） DC films were made by mixing SrAl₂O₄:Eu²⁺, Dy³⁺powders in PVDF or PMMA via tape casting process. The effects of powder content, filmthickness on the light transmittance were tested. For PVDF films, whenphosphor content was7wt%and thickness was0.05mm, the lighttransmittance was85%; and for PMMA films, when phosphor content was10wt%and thickness was0.1mm, the light transmittance was92%. Thephotocurrent-voltage characteristics were measured after covering DC filmsonto the surface of Si solar cells. SrAl₂O₄:Eu²⁺, Dy³⁺/PVDF films couldincrease the Vocof the cell from0.534V to0.559V, and SrAl2O4:Eu2+,Dy3+/PMMA films increased power conversion efficiency（η） by0.43%. It wasseen that PMMA could be used to make DC films for solar cells.（3） SrAl₂O₄:Eu²⁺, Dy³⁺/PMMA films （content was10wt%and thicknesswas10m） was directly coated on solar cell by screen-printing technique. Apositive effect on the photoelectric conversion of solar cells was got:ηwasincreased from7.96%to8.96%, andηwas1%, higher than that of reportedon the same kind of efficiency. One of the reasons were that phosphorsprovided solar cells with more visible light turned from ultraviolet light. Theother reason was screen-printing technique made the film more closely withsolar cell to greatly eliminate the energy loss on surface, which helped toincrease conversion efficiency of solar cells.