Researchers have developed a novel thin-film coating providing an unparalleled
level of surface
passivation of crystalline silicon solar cells. Using Oxford Instruments'
FlexAL® ALD tool, the team from
the Eindhoven University of Technology (TU/e) showed that ultra-thin aluminium
oxide layers deposited
by remote plasma ALD outperform existing passivation coatings in terms of eliminating
the - normally
significant - electronic losses at solar cells' back and front surfaces.
Oxford Instruments’ Flexal® ALD Tool
Oxford
Instruments customised its popular FlexAL and OpAL™ tools for this
specific application, which has resulted in multiple sales to the rapidly growing
solar cell industry.
The development facilitates breakthrough efficiencies for an important class
of solar cells. This was
recently demonstrated in collaboration between TU/e and the leading Fraunhofer
Institute for Solar
Energy Research (ISE) in Germany. An efficiency of 23.2% was obtained for PERL
solar cells based on
n-type silicon by the application of an ultra-thin aluminium oxide layer at
the front of the solar cell. To
date the p-type front of this class of solar cells was hard to passivate and
the relative efficiency
improvement of 6% is therefore a significant advance.
Chris Hodson, ALD Product Manager at Oxford Instruments Plasma Technology
is delighted with this
research, “Dr. Kessels and the Plasma & Materials Processing (PMP)
group at TU/e are pushing the boundaries of ALD research into new application
areas. This key technology breakthrough using our
ALD tools is creating real interest, and I am confident our continued collaboration
with TU/e will bring
further advances in this and other technology areas.
Dr. Kessels comments, “Surface passivation is a major issue for crystalline
silicon solar cell technology,
a type of solar cell that dominates 90% of the photovoltaic market. Many thin
film coatings have been
studied to reduce electronic losses at the front and rear surfaces of the solar
cells. Until recently none
were found to satisfactorily passivate the highly doped p-type surfaces of next-generation
solar cells
based on the more cost-effective n-type base material. During the recent PhD
research of Dr. Hoex, we
have shown the unprecedented high level of built-in negative charges in an ultra-thin
aluminium oxide
layer deposited by plasma ALD can almost entirely eliminate electronic loses
at the solar cell surfaces.
Aluminium oxide has recently gained the attention of the photovoltaics community
as a versatile and
compatible material that is expected to facilitate several advances in solar
cell design and technology.”