LEUVEN, BelgiumResearchers at IMEC, a research centre for nanoelectronics and nanotechnology, have created a high-efficiency single-junction gallium-arsenide solar cell on a germanium substrate, which was provided by Umicore of Brussels. Shown is a single-junction gallium- arsenide solar cell on a germanium substrate.The cell, grown epitaxially on a substrate with an improved microdefect distribution, measures 0.25 cm2. The maximum conversion efficiency of 24.7 per cent was achieved with an open-circuit voltage of 999 mV, a short-circuit current of 29.7 mA/cm2 and a fill factor of 83.2 per cent. The efficiency was measured and confirmed by the National Renewable Energy Laboratory in Golden, Colo., USA. IMEC specializes in hybrid monolithic/mechanically stacked triple-junction solar cells consisting of top cells made of III-V materials and bottom cells made of germanium. The research centre is targeting a conversion efficiency of greater than 35 per cent. The solar cell stacks can be used in satellites and in Earth-based solar concentrators.