Fabrication and characterization of GaAs solar cells on copper substrates

This letter presents performance comparison between a GaAs/mirror/copper thin-film solar cell and a conventional GaAs solar cell with a thick GaAs substrate. The GaAs thin-film solar cell was fabricated by transferring a GaAs solar cell onto a AuGe/Au mirror-coated copper substrate. With the aid of the excellent copper conductor, the thin-film solar cell exhibits significant improvement in both open-circuit voltage and short-circuit current density. The improved current-voltage (I-V) performance of the thin-film solar cell originates from the following two factors: reduced reverse saturation current by good heat dissipation of copper and enhanced light absorption by the highly reflective AuGe/Au mirror. The role of the mirror can further be verified in the measurement of external quantum efficiency (EQE) response where the thin-film solar cell exhibits a larger EQE response in the wavelength range of 700-900 nm than the conventional GaAs solar cell with the same active absorbing thickness.