Upconversion to enhance silicon solar cell efficiency - detailed experimental analysis with both coherent monochromatic irradiation and white light illumination

Upconversion (UC) of sub-band-gap photons is a promising approach to increase solar cell efficiencies, because it makes these sub-band-gap photons useful as well. We investigate the application of -NaYF4:20% Er3+ to silicon solar cells. We determine the external quantum efficiency of an UC silicon solar cell, both under monochromatic excitation and under white light illumination. We demonstrate that an UC silicon solar cell responds under white light with an average UC efficiency of 1.07 ± 0.13% in the spectral range from 1460 to 1600 nm. Concepts are discussed how the narrow absorption range of the UC material can be overcome.