"This degradation is observed but not yet fully understood," she says,
explaining that the power output of solar cells is seen to decline as
they age. "Currently, up to 20 % efficiency loss is due to this effect,
although the reasons are still unknown. Industry is trying to tackle the
problem by using better quality, but more expensive materials, or by
using different dopants in the silicon, but to date there is no
This is where Prof. Savin’s background in electronic engineering has
come in useful: having studied Microelectronics at Helsinki University
of Technology (TKK), she is currently Head of the Electron Physics Group
in the Micro- and Nano-Sciences Department at the Aalto University
School of Electrical Engineering in Finland.
In recent years, the technologies and materials used in
microelectronics and silicon-based photovoltaic (PV) solar cells have
been converging. Prof. Savin is now trying to apply her previous
research to solve a problem in this new field.
"My proposal is that copper impurities in the silicon, reacting with
light, cause the decline in power output," she says. "There is always
copper in the silicon used in large PV cells – either pre-existing
impurities or resulting from the production process – and this copper
can move around, diffusing through the silicon, even at room
"In my PhD I studied copper in microelectronics – in particular,
copper contamination in silicon," she continues. "I used light to make
the copper electrically active. I wanted to produce this effect, but my
hypothesis is that this also explains the degradation the PV industry
would like to prevent. When you expose photovoltaic cells to sunlight,
it makes the copper impurities electrically active, they move and
accumulate so that existing clumps grow bigger, and this is what damages
the PV cell and disrupts the flow of electric current."
Prof. Savin’s research group is therefore developing a solution
using a negative charge at the surface of the silicon – exploiting the
insulation properties of the protective oxidised coatings common to most
PV cells. The surface therefore attracts copper ions – instead of them
accumulating in clusters – and the flow of electric power remains
"The degradation effect is slow, so the experiments have to last
days," she says. "The ERC’s support has meant we can focus on solving
this issue for the next five years – with a postdoc and PhD student
devoted to it – and use the specialised tools available at the Micronova
facility for controlling copper-contaminant levels."
Micronova is Finland’s national research infrastructure for micro-
and nanotechnology, run by the VTT Technical Research Centre of Finland
and Aalto University. Its dedicated equipment allows Prof. Savin to
study the effects of copper in silicon alone, while avoiding
cross-contamination from other impurities.
"This project is basic science, but the production capacity and
market for PV technology is already huge, so there will be a big
technological impact if it works – and applications could potentially
arrive quite quickly," she says. "On the other hand, even if it doesn’t
work at an industrial scale, a better understanding of the science of
this effect could also be a significant result, leading to other, better
solutions in the future." After hydro and wind power, solar energy
based on photovoltaics is already the third most important renewable
energy source – with more than 100 GW of capacity installed globally.
So, by continuing with her work, Prof. Savin may help to bring an energy
revolution – based on reliable, renewable power – one step closer.
"My dream is that technology developed by me will be utilised by the global photovoltaic industry," she concludes.
- Source: Prof. Hele Savin
- Project coordinator: Aalto University School of Electrical Engineering, Finland
- Project title: Riddle of light-induced degradation in silicon photovoltaics
- Project acronym: SOLARX
- Institution website
- FP7 funding programme (ERC call): Starting Grant 2012
- EC funding: EUR 850 000
- Project duration: 5 years