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Researchers from École polytechnique fédérale de Lausanne in Switzerland are fine tuning perovskite solar cells with a "burst" of vacuum flash.

Clean Power

Coal-Killing Perovskite Solar Cell Beats 20% Efficiency Mark, Aims For 30%

Researchers from École polytechnique fédérale de Lausanne in Switzerland are fine tuning perovskite solar cells with a “burst” of vacuum flash.

The lab of perovskite solar cell pioneer Michael Graetzel is at it again. The Switzerland-based research team has  been fine-tuning its method for growing the finicky crystals on a thin film, and the latest variation injects a “burst” of vacuum flash into the mix. If commercialized, the new technique could lower manufacturing costs, and keep the cost of solar power heading on a downward spiral.

perovskite solar cell Graetzel

The Coal-Killing Perovskite Solar Cell

When presumptive Democratic nominee Hillary Clinton said that “we’re” going to put coal miners and mining companies out of business earlier this year, she most likely did not mean that Professor Graetzel and his team would be directly responsible for the death of coal. However, solar-to-electricity technology has been rapidly marching past the limits of coal-to-electricity technology, and the perovskite field is a good example.

For those of you new to the topic, perovskite crystals are relatively easy to manufacture, and they are much cheaper than silicon.

Solar researchers began tinkering with perovskites in earnest less than ten years ago. From a starting point of less than 4% solar conversion efficiency in 2009, research teams around the globe have quickly teased the rate up into the double digits while steadily pushing down costs.

Recipe For A Low Cost Solar Cell

The basic technique for creating perovskite solar cells is to ‘grow’ the crystals on a thin film. The challenge is to make that layer as uniform as possible, while making each grain of crystal approach a relatively large size.

It’s a complicated dance that involves spraying a solution of raw materials onto conductive glass and applying heat. The crystals form as the solution dries.

Graetzel’s team has found that the process can be manipulated to create a more uniform layer. One technique involves spinning off excess moisture, literally by spinning the glass while the solution is drying:

solar cell efficiency perovskite 2

The new vacuum flash technique provides a twofer. If you’re feeling ambitious, you can look it up in the journal Science under the title, “A versatile vacuum-flash assisted solution process for high-efficiency large-area perovskite solar cells.”

For those of you on the go, vacuum flash refers to the vaporization that occurs when a heated liquid is briefly exposed to a vacuum:

solar cell effciency perovskite 1

Graetzel’s team found that the process is ideal for removing volatile compounds in the excess liquid, helping to ensure that the resulting film grows uniformly. The ‘seeds’ left behind also tend to produce high quality crystals, which boosts conversion efficiency.

According to the lab, the conversion efficiency reached through the new fabrication method topped out at more than 20%.

Aside from tweaking the fabrication process, Graetzel’s lab has also been addressing the cost of materials used in the solution for growing perovskite crystals. Last January, for example, the lab announced that it had found a replacement for one such material, yielding the same conversion efficiency at one-fifth the cost.

More Life For Silicon Solar Cells

Perovskite solar cells offer another pathway for transitioning out of coal, but it’s too soon to sound the death knell for silicon.

One main obstacle is the lead component in conventional perovskite solar cells. In a conversation with CleanTechnica a couple of years ago, Graetzel cautioned that the commercial use of perovskite solar cells could be limited to secure sites where cradle-to-grave materials management can virtually eliminate the risk of lead hazards.

Assuming the lead issue can be resolved, Graetzel foresees that a combination solar cell with perovskites layered onto silicon could jump over the 30% efficiency mark. Such a solar cell would be considerably cheaper than silicon alone.

In that case, rather than killing off silicon solar cells, perovskites could actually extend the lifespan of the silicon industry — at least until something cheaper comes along.

Photo (cropped): via EPFL (École polytechnique fédérale de Lausanne), other images are screenshots.

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Tina specializes in military and corporate sustainability, advanced technology, emerging materials, biofuels, and water and wastewater issues. Tina’s articles are reposted frequently on Reuters, Scientific American, and many other sites. Views expressed are her own. Follow her on Twitter @TinaMCasey and Google+.


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