Thin film GaAs solar cell enabled by direct rear side plating and patterned epitaxial lift-off

Abstract

III-V based solar cells have demonstrated highest conversion efficiencies. To enable further integration into the photovoltaic industry cost reduction is required. We present a processing scheme to fabricate inverted GaAs solar cells via patterned direct rear side plating and subsequent epitaxial lift-off. Contact resistances well below 10−4 Ω cm2 are demonstrated using direct nickel plating on a palladium activated surface. In the presented process etching of the AlAs sacrificial layer with hydrofluoric acid is accelerated due to simultaneous attack through the patterned structure, leading to fast lift-off times of below 2:20 h for a four-inch wafer with 8.0×8.5 mm2-sized lift-off areas. We find that the homogeneity of direct plating is crucial for the stability of the process. Characterization results of inverted GaAs thin film cells are presented. The presented processing scheme is a promising approach for the processing of thin film solar cells which enables low-cost rear side metal deposition and a fast lift-off time.