Record efficiency of 18.7 percent for flexible CIGS solar cells on plastics

May 19, 2011
Record efficiency of 18.7 percent for flexible CIGS solar cells on plastics
Flexible thin film CIGS solar cell on polymer substrate developed at Empa (Copyright: Empa)

Scientists at Empa, the Swiss Federal Laboratories for Materials Science and Technology, have further boosted the energy conversion efficiency of flexible solar cells made of copper indium gallium (di)selenide (also known as CIGS) to a new world record of 18.7 percent -- a significant improvement over the previous record of 17.6 percent achieved by the same team in June 2010. The measurements have been independently certified by the Fraunhofer Institute for Solar Energy Systems in Freiburg, Germany.

It's all about the money. To make solar electricity affordable on a large scale, scientists and engineers worldwide have long been trying to develop a low-cost solar cell, which is both highly efficient and easy to manufacture with high throughput. Now a team at Empa's Laboratory for Thin Film and , led by Ayodhya N. Tiwari, has made a major step forward. "The new record value for flexible CIGS solar cells of 18.7% nearly closes the "efficiency gap" to solar cells based on (Si) wafers or CIGS thin film cells on glass", says Tiwari. He is convinced that "flexible and lightweight CIGS solar cells with efficiencies comparable to the "best-in-class" will have excellent potential to bring about a paradigm shift and to enable low-cost in the near future."

One major advantage of flexible high-performance CIGS solar cells is the potential to lower manufacturing costs through roll-to-roll processing while at the same time offering a much higher efficiency than the ones currently on the market. What's more, such lightweight and flexible solar modules offer additional cost benefits in terms of transportation, installation, structural frames for the modules etc., i.e. they significantly reduce the so-called "balance of system" costs. Taken together, the new CIGS polymer cells exhibit numerous advantages for applications such as facades, solar farms and portable electronics. With high-performance devices now within reach, the new results suggest that monolithically-interconnected flexible CIGS solar modules with efficiencies above 16% should be achievable with the recently developed processes and concepts.

Record efficiency of 18.7 percent for flexible CIGS solar cells on plastics
Improvement in energy conversion efficiency of flexible CIGS solar cells on polymer film.

In recent years, thin film photovoltaic technology based on glass substrates has gained sufficient maturity towards industrial production; flexible CIGS technology is, however, still an emerging field. The recent improvements in efficiency in research labs and pilot plants – among others by Tiwari's group, first at ETH Zurich and since a couple of years now at Empa – are contributing to performance improvements and to overcoming manufacturability barriers.

Working closely with scientists at FLISOM, a start-up company who is scaling up and commercializing the technology, the Empa team made significant progress in low-temperature growth of CIGS layers yielding flexible CIGS cells that are ever more efficient, up from a record value of 14.1% in 2005 to the new "high score" of 18.7% for any type of flexible solar cell grown on polymer or metal foil. The latest improvements in cell efficiency were made possible through a reduction in recombination losses by improving the structural properties of the CIGS layer and the proprietary low-temperature deposition process for growing the layers as well as in situ doping with Na during the final stage. With these results, polymer films have for the first time proven to be superior to metal foils as a carrier substrate for achieving highest efficiency.

Record efficiencies of up to 17.5% on steel foils covered with impurity diffusion barriers were so far achieved with CIGS growth processes at temperatures exceeding 550°C. However, when applied to steel foil without any diffusion barrier, the proprietary low temperature CIGS deposition process developed by Empa and FLISOM for polymer films easily matched the performance achieved with high-temperature procedure, resulting in an efficiency of 17.7%. The results suggest that commonly used barrier coatings for detrimental impurities on metal foils would not be required. "Our results clearly show the advantages of the low-temperature CIGS deposition process for achieving highest efficiency flexible solar cells on polymer as well as metal foils", says Tiwari. The projects were supported by the Swiss National Science Foundation (SNSF), the Commission for Technology and Innovation (CTI), the Swiss Federal Office of Energy (SFOE), EU Framework Programmes as well as by Swiss companies W.Blösch AG and FLISOM.

The continuous improvement in energy conversion efficiencies of flexible CIGS is no small feat, says Empa Director Gian-Luca Bona. "What we see here is the result of an in-depth understanding of the material properties of layers and interfaces combined with an innovative process development in a systematic manner. Next, we need to transfer these innovations to industry for large scale production of low-cost to take off." Empa scientists are currently working together with FLISOM to further develop manufacturing processes and to scale up production.

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Sonhouse
4 / 5 (1) May 19, 2011
I don't see anything here about life span of these cells, also they don't mention how much they would cost per watt. How well do they hold up in intense summer sun, for instance. How well would they hold up under winter ice and snow? If they only last say, 1/3 the span of silicon cells, they would not have gained much if anything.
Scottingham
not rated yet May 19, 2011
= watts per square meter?
SteveL
4.3 / 5 (6) May 19, 2011
This is just a new development, there won't be any life span information for a while.
that_guy
not rated yet May 19, 2011
and it has only been done in a lab...they probably haven't yet extrapolated the manufacturing costs on a large scale.
IngDutch
3 / 5 (1) May 19, 2011
I don't see any profit with these above silicium thin film. Silicium has 17% in mass production, with theoretical 24% possibility. The materials used in these solar cells are scars and could be hazardous, when released in the nature. Even tough the first paragraph talks about money it does not quote a prospect in cost per Watt hour. Thin being cheaper then normal solar cells is a given, less materials = less money.
IngDutch
5 / 5 (2) May 19, 2011
= watts per square meter?


This depends on the intensity of the sun, hours of sun light and efficiency. There is a standard model of light to calculate the efficiency. The other two factors depend on the deployment of the solar panel. Where, what angle, etc. etc. So you could calculate the watts per square meter if you know where you will be placing the solar panel.
that_guy
5 / 5 (1) May 19, 2011
who would give steveL a 1 for a pertinent observation?? I give a 5 to compensate.

@ dutch - solar array watt per square meter is generally based on and average of what it will generate under set conditions, which I believe to be peak noon or yearly average using the mid temperate climate conditions. I admit I don't know enough to actually give you the exact method of measurement.

I looked up some sites for solar panels, and they say rule of thumb is 8-10 watts a square foot (appx 73-90 watts per meter squared) for current home installations.

It also says that current home systems run 7-17% efficiency, so I would expect this thin film version to run at the high end of that range.

That said, your mileage may vary drastically due to the many variables involved.

solar-estimate.com
El_Nose
not rated yet May 23, 2011
after what that guy said...

solar cells normally last a really long time barring getting hit by flying debris from a major storm -- regularlly watering them to remove dust is a bonus to effeciency over time if you are in a low rainfall area -- but they normally last as long as a mortgage
SteveL
not rated yet May 23, 2011
Much like an LED, the life of a PV panel is based on useful output compared to the peak panel rating. Many are considered to have used up their life after their output has dropped 20% or so. For many panels this reduced output is expected after 20 - 25 years of service. At this point the panel will still put out 80% of its peak rated capacity, but this capacity will continue to steadily decrease at a rate of about 1% per year.

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