Feb. 25, 2008 – IMEC says it has achieved a record 24.7% efficiency with a single-junction GaAs solar cell grown epitaxially on a Ge substrate, part of work to develop a hybrid monolithic/mechanically stacked triple-junction solar cell.

The 0.25 sq. cm cell has an open-circuit voltage of 999mV, short circuit current of 9.7mA/sq. cm, and fill factor of 83.2%. IMEC explained in a statement that this particular type of solar cell incorporates stacks of solar cells made from different semiconductors to absorb as much solar spectrum as possible. The group’s research is focusing on stacked cells with the top cells of III-V materials, and bottom cells made from Ge, a combination for which it is targeting at least 35% efficiency. End use applications include satellites and earth-based concentrators.

Performance characterization of IMEC’s GaAs cell, measured by NREL. (Source: IMEC)

Back in October IMEC said it has achieved >17% efficiency with thin-film silicon solar cells, with >20% efficiencies “definitely within reach.” It also said it is nearing the theoretical efficiency limits of Ge solar cells, currently topping 8.5%.