Plasmonically Enhanced Spectral Upconversion for Improved Performance of GaAs Solar Cells under Nonconcentrated Solar Illumination

Spectral upconversion has the potential to compensate for sub-bandgap transparency of single-junction solar cells. Here a composite module of GaAs solar cells is presented that can improve their one-Sun photovoltaic performance by capturing long-wavelength photons below the bandgap via plasmonically enhanced spectral upconversion. Ultrathin, microscale GaAs solar cells released from the growth wafer and etched with a bottom contact layer are printed on a polymeric waveguide containing NaYF₄:Er³⁺, Yb³⁺ upconversion nanocrystals (UCNC), coated on a plasmonic reflector composed of hole-post hybrid silver nanostructure. The photovoltaic efficiency of GaAs microcells on a UCNC-incorporated plasmonic substrate is increased by ∼6.4% (relative) and ∼11.8% (relative), respectively, compared to those on a nanostructured silver reflector without UCNC and on a plain silver reflector with UCNC, owing to the combined effects of local electric-field amplification to enhance the absorption of UCNC, augmented upconverted emission via coupling into radiative modes, as well as waveguided photon concentration.