Imec Makes Epitaxial Solar Cells with Higher Efficiencies

Labels: PV Cells & Modules, R&D, Europe, Silicon, Research - Universities

20 July 2010

Imec, Europe’s largest independent research center in nanoelectronics and nano-technology, reports that it has achieved large-area (70 cm²) epitaxial solar cells with efficiencies of up to 16.3% on high-quality substrates and efficiencies of up to 14.7% on large-area low-quality substrates.

The work was done within Imec’s silicon solar cell industrial affiliation program, which explores and develops process technologies that reduce silicon use while increasing cell efficiency and further lowering the cost per Watt peak. Epitaxial solar cells could reduce the amount of silicon required to make a solar cell by using only a thin film of active silicon on top of a low-cost substrate, but the challenge is to find an optimal combination of cell efficiency, large-scale production, and manufacturing cost.

To make the solar cells, epitaxial silicon stacks (20-um thick) were placed on highly-doped high-quality substrate and on a low-cost upgraded metallurgic grade (UMG)-type, multi-crystalline silicon substrate. The light-trapping scheme consisted of plasma texturing the front surface and positioning an internal porous silicon Bragg reflector at the epitaxial/substrate interface to improve the optical confinement of light in the active part of the cell. The cells on the high-quality substrate had copper plating contacts, and those on the low-quality substrates had screen-printed metal contacts. The epitaxially grown ‘wafer equivalent’ substrates are fully compatible with standard industrial (bulk) solar cell processing.

“These efficiencies of up to 16.3% on high-quality substrates and of up to 14.7 % on low-cost substrates show that industrial-level efficiencies are within reach for this technology,” said Jef Poortmans, director imec energy/solar program. “By implementing copper-based contact schemes, we can further increase the efficiency, making epitaxial thin-film silicon solar cells on low-cost wafers an interesting industrial technology.”

Imec has made a large-area (70 cm2) epitaxial solar cell with
an efficiency of up to 16.3% on high-quality substrate