A series of joint sub-projects and work-packages has enabled the scientists
to develop a new, less expensive grade of raw material for solar cells. And
the best news is that the new modules are just as efficient as current solar
cells.
Pleased solar-cell scientists
The EU's three-year FoXy programme has come to an end. The research group
is very satisfied, and the EU Commission is handing out praise.
SINTEF has coordinated
this major programme that rejoices in the long name: "Development of solar-grade
silicon feedstock for crystalline wafers and cells by purification and crystallisation",
which has been simplified to "FoXy". Together with ten other participants
from various European nations, the scientists have been developing a "good
enough" grade of silicon for solar cell production.
And there has been no lack of results: a series of joint sub-projects and work-packages
has enabled the scientists to develop a new, less expensive grade of raw material
for solar cells. And the best news is that the new modules are just as efficient
as current solar cells.
Less pollution
"We are very proud of what we have done," says Marisa Di Sabatino
of SINTEF Materials and Chemistry. "Many people before us have been working
on solar energy, but our results are actually quite important."
The ambition of the programme has always been to develop a new material that
would make future solar cells both at least as efficient as those of today and
cheaper than them.
"We started out from metallic silicon that contains around 1% impurities
- which is not good enough for use in solar cells. We attempted both to
reduce the impurities in the metallic silicon and to cut down the amount of
impurities that are already in the raw material by means of heat treatment,
for example," explains Di Sabatino.
Direct route
The research group managed to shorten the long production process currently
employed by most solar cell manufacturers by adopting a simpler, more direct
route. They managed this by using a special smelter and a kiln that removes
trace of carbon.
The scientists used pure carbon that contaminates the silicon far less than
coke or coal, as well as ultrapure quartz from the Norwegian County of Nordland.
This process is much less costly and energy-intensive than the conventional
chemical process.
"With today's solar cells, the energy used to produce them is paid
off in the course of two years:. With the new materials, the payback time could
be as little as six months," says Di Sabatino.
Understanding the relationships
Impurities in silicon cause problems. For example, silicon recycled from industry
contains boron and/or phosphorus that can alter the electrical characteristics
of the material. Other contaminants can, for example, lead to the formation
of poor-quality particles that in turn mean less efficient solar panels installed
on our roofs.
However, the project group concluded that even if contaminants are present,
we can still produce good-quality material with the aid of special procedures
that reduce or eliminate them. It is just a matter of understanding how things
fit together, so that things can be done in a better way; and the results of
FoXy have helped the researchers towards a better understanding of what takes
place in the process.
For example, the FoXy scientists have patented a new, more stable, passivation
process - a high-temperature treatment process that protects the surface
of the solar cells, making them more efficient and resistant to temperature
changes.
Characteristics of cells
Good material is essential, but even more important are the solar cells themselves.
In the course of their work on the FoXy programme, the scientists have produced
modules that incorporate new ways of assembling the individual cells. These
are normally put together with the n (-) and p (+) silicon laid in contact horizontally.
Now they are placed vertically in the panel, saving space, allowing more cells
to be inserted and reducing the probability of technical failure.
The work of the FoXy scientists ended up with full-scale trials of the new
modules. The results were encouraging; as well as being more robust, they were
just as efficient as today's solar cells.
"They will also be cheaper," says Di Sabatino. The aim of the FoXy
partners is that when the modules reach the production stage, they will be one
euro cheaper per Watt of electricity generated .
Although the programme has come to an end, the researchers hope to be able
to continue their efforts. If they do, the next phase of the work will focus
on developing thinner wafers. Today, the standard thickness is 180 - 200
micrometres, and the aim is to halve that, which will save valuable material.
The challenge lies in how the material is handled; it must be strong enough
to be cut without fracturing. This will be the subject of a new proposal that
we have just sent to Brussels for a project with eight other partners, and we
are keeping our fingers crossed that we will be awarded it," says Di Sabatino.
