Shalav, A.Richards, B. S.Trupke, T.Krämer, K. W.Güdel, H. U.2015-12-042015-12-040003-6951http://hdl.handle.net/1885/17011Erbium-doped sodium yttrium fluoride (NaYF₄:Er³⁺) up-conversion phosphors were attached to the rear of a bifacial silicon solar cell to enhance its reponsivity in the near-infrared. The incident wavelength and light intensity were varied and the resulting short circuit current of the solar cell was measured. A close match between the spectral features of the external quantum efficiency and the phosphor absorption is consistent with the energy transfer up-conversion process. The peak external quantum efficiency of the silicon solar cell was measured to be (2.5±0.2)% under 5.1 mW laser excitation at 1523 nm, corresponding to an internal quantum efficiency of 3.8%.http://www.sherpa.ac.uk/romeo/issn/0003-6951..."Publishers version/PDF may be used on author's personal website, institutional website or institutional repository" from SHERPA/RoMEO site (as at 4/12/15). Copyright 2005 American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physics. The following article appeared in Applied Physics Letters and may be found at https://doi.org/10.1063/1.18445922005-12-2810.1063/1.1844592