Long Afterglow SrAl2O4:Eu2+,Dy3+ Phosphors as Luminescent Down-Shifting Layer for Crystalline Silicon Solar Cells

SrAl2O4:Eu2+,Dy3+ phosphors can convert near ultraviolet light with lower sensitivity to the solar cell to yellow-green light at which the solar cell has higher sensitivity and exhibit the excellent luminescent property of long persistence. Therefore, in this study, the authors firstly synthesized the fine SrAl2O4:Eu2+,Dy3+ phosphors and then produced SrAl2O4:Eu2+,Dy3+/SiO2 composite films as spectral shifters to understand the effects of SrAl2O4:Eu2+,Dy3+ phosphor on photoelectric conversion efficiencies of a crystalline silicon photovoltaic module. Under one sun illumination, the composite film containing an appropriate amount of SrAl2O4:Eu2+,Dy3+ phosphor enhances the photoelectric conversion efficiency of the cell through spectral down-shifting as compared to the bare glass substrate, and the maximum achieves 11.12%. In contrast, the commercial SrAl2O4:Eu2+,Dy3+ phosphor composite film is not effective for improving the photoelectric conversion efficiency because of the relatively lower visible light transmittance of film caused by the large aggregates. After one sun illumination for 1min, the light source was turned off, and the cell containing the synthesized SrAl2O4:Eu2+,Dy3+ phosphor still shows an efficiency of 1.16% in the dark due to the irradiation by the long persistent light from SrAl2O4:Eu2+,Dy3+, which provides a possibility to fulfill the operation of solar cells even in the dark.