Imec realized large-area
(70cm2) epitaxial solar cells with efficiencies of up to 16.3% on high-quality
substrates. And efficiencies of up to 14.7% were achieved on large-area low-quality
substrates, showing the potential of thin-film epitaxial solar cells for industrial
The results were achieved within imec’s silicon solar cell industrial
affiliation program (IIAP) that explores and develops advanced process technologies
aiming a sharp reduction in silicon use, whilst increasing cell efficiency and
hence further lowering substantially the cost per Watt peak.
Besides wafer-based bulk silicon solar cells imec aims at developing epitaxial
thin-film (<20µm) silicon solar cells grown on low-cost silicon carriers
within its silicon solar cell IIAP.. The epitaxial thin-film process on low-cost
silicon carriers is generically similar to the bulk process and the epi-process
can be implemented with limited equipment investment in an existing crystalline
silicon solar cell manufacturing line. To improve the optical confinement of
light in the active part of the cell, a buried porous Si reflector is developed.
Imec realized 20µm thick high-quality epitaxial silicon stacks both on
top of a highly-doped high-quality substrate and on a low-cost, UMG (upgraded
metallurgic grade)-type, multi-crystalline Si substrate. The p+-type back surface
field (BSF), the p-type base and the n-type front-side emitter were grown by
chemical vapor deposition. The light-trapping scheme consists of plasma texturing
of the front surface in combination with an internal porous silicon Bragg reflector
positioned at the epitaxial/substrate interface. The cells on the high-quality
substrate are contacted with copper plating. For the cells made on the low-quality
substrates, the metallization is realized with screenprinting, which is the
final step after the formation of the diffused front surface field (FSF) and
the silicon nitride antireflection coating. In this way, 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 to14.7 % 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 performs world-leading research in nanoelectronics. Imec leverages its
scientific knowledge with the innovative power of its global partnerships in
ICT, healthcare and energy. Imec delivers industry-relevant technology solutions.
In a unique high-tech environment, its international top talent is committed
to providing the building blocks for a better life in a sustainable society.
Imec is headquartered in Leuven, Belgium, and has offices in Belgium, the Netherlands,
Taiwan, US, China and Japan. Its staff of more than 1,750 people includes over
550 industrial residents and guest researchers. In 2009, imec's revenue (P&L)
was 275 million euro.
Imec is a registered trademark for the activities of IMEC International (a
legal entity set up under Belgian law as a "stichting van openbaar nut”),
imec Belgium (IMEC vzw supported by the Flemish Government), imec the Netherlands
(Stichting IMEC Nederland, part of Holst Centre which is supported by the Dutch
Government), imec Taiwan (IMEC Taiwan Co.) and imec China (IMEC Microelectronics
(Shangai) Co. Ltd.).