CaF2:Ce3+/Yb3+ hollow spheres luminescence downconversion property optimize anti-reflective coatings for solar cells

• CaF2:Ce3+/Yb3+ phosphors were synthesized by a facile hydrothermal approach.
• The effects of doping concentration and lifetime on PL intensity were investigated.
• The AR coatings and the phosphors were combined to get the bi-functional films.
• The enhancement on photovoltaic efficiency of silicon solar cells were discussed.

Highly uniform and well dispersed CaF2 hollow spheres codoped with rare-earth (RE) ions Ce3+ and Yb3+ were synthesized by a facile and effective hydrothermal approach based on Ostwald ripening mechanism. The chosen phosphors were added in the SiO2 sols so as to get the anti-reflection (AR) coatings with wavelength conversion property, further to availably enhance the photovoltaic performance of solar cells. The ultraviolet (UV) light excitation induced the transition from 5D to 4F energy levels of Ce3+ with two emission bands centering at 317 nm and 336 nm. Through an efficient energy transfer process, the intense characteristic near-infrared (NIR) emission of Yb3+ peaking at 965 nm and 1026 nm attributed to the transition of 2F5/2 to 2F7/2, which is just matched the spectral response of Si band gap. In addition, all of the AR coating films containing phosphors showed an incredible transmittance performance in visible and NIR region as well as a preferable photo-electricity response. CaF2:Ce3+–Yb3+ AR coating film could effectively improve the photoelectric conversion efficiency by 0.16%, 0.50% and 1.20% compared to CaF2:Ce3+ AR coating film, SiO2 AR coating film and pure glass respectively. This work may promote a new platform and wider application of the wavelength conversion materials for silicon solar cells.