A new perovskite solar cell from Belgium’s IMEC research hub logs a conversion efficiency of 23.9%, which according to IMEC beats conventional silicon solar cells at their own game. The news is yet another indication that the cost of solar power still has a long way to go before it hits bottom.
Perovskite Solar Cells: It’s Such A Long Way Down
IMEC seems to be aiming at a moving target — Japan’s Kaneka Corp., for example, reported a 26.3% conversion efficiency for its new silicon solar cell last spring — but who’s counting? The main point of the story is perovskite.
Perovskite refers to a class of crystalline materials that can be easily synthesized to mock the properties of the naturally occurring mineral perovskite.
Perovskites are also incredibly cheap compared to silicon, and they are compatible with high volume, low cost manufacturing processes.
Even without perovskites, the cost of solar power is already competitive with fossil fuels in some markets. If and when perovskites break through commercially, costs will drop even further.
Researchers began tinkering around with perovskites in earnest just a few years ago, and progress in the field has been humming along at a rapid pace. The US National Renewable Energy Laboratory is particularly enthused:
Work on solar cells using perovskite material has advanced rapidly as a result of the materials excellent light absorption, charge-carrier mobilities, and lifetimes, resulting in high device efficiencies with significant opportunities to realize a low-cost, industry-scalable technology.
Of course, there’s a catch — a couple of catches, in fact. Perovskites don’t like humidity, and so far researchers have been leaning on lead as a key component.
Addressing those challenges while pumping up conversion efficiency and keeping manufacturing costs down is where it gets interesting.
IMEC Gets ThisClose To 24%
Just a few weeks ago, Korea’s UNIST (Ulsan National Institute of Science and Technology) reported that it hit the 22.1% mark with a low cost manufacturing process for inorganic-organic hybrid perovskite solar cells, so the IMEC mark of 23.9% represents a significant jump up in a short period of time.
To overcome the challenges, IMEC modded a perovskite solar cell with silicon, a pathway that other researchers have also been pursuing.
IMEC explains why the perovskite-silicon combo is so attractive:
…perovskite solar cells or modules may also be used to boost standard silicon (Si) solar technology when engineered to absorb a spectral range that is complementary to the optical range of silicon cells. By stacking the perovskite solar cells or modules on top of Si solar cells, power conversion efficiencies above 30 percent can potentially be achieved, thereby surpassing the efficiencies of the best single junction Si solar cells.
Work on the new solar cell is part of IMEC’s ongoing partnership with the Netherlands/Belgium/Germany research hub Solliance, and it looks like all that brain power is paying off.
The partnership produced an earlier iteration of the new cell last year with a conversion efficiency of only 20.2%.
So, how did they bump it up another 3.7% in just one year?
According to IMEC and Solliance, one key difference was switching up the type of perovskite used in the solar cell.
The newer version uses the perovskite CsFAPbIBr (notice the Pb in there), which tuned the conversion efficiency of the perovskite layer to 15.3%.
The research team also gave the architecture of the stacked perovskite-silicon combo a makeover. They texturized the topmost layer to reduce reflection, and they slipped a matching refractive liquid between the perovskite and the silicon.
The Pathway To Millions Of Perovskite Solar Panels
The IMEC research team has been keeping a close eye on manufacturing costs, and with that in mind, the new solar cell was designed with aperture areas of up to four square centimeters.
That has a dampening effect on conversion efficiency — the researchers actually achieved 25.3% with smaller apertures — but the larger size is more consistent with current manufacturing processes.
Meanwhile, over here in the US, researchers at Columbia University have figured out why perovskite solar cells perform so well, even when they are defective (silicon is expensive partly because it has to be flawless to perform well).
The discovery could lead to new, more effective forms of perovskite.
That pathway also has the potential for developing new forms of perovskite that don’t incorporate lead.
If all goes according to plan, it looks like the US Energy Department will reach its goal of sinking the cost of solar power down to the range of 2-3 cents per kilowatt hour by 2030.
That’s a mighty big “if,” considering that US President* Donald Trump is not exactly a big fan of renewable energy (the sole exception seems to be solar panels on walls).
On the other hand, despite Trump’s pro-coal rhetoric Energy Secretary Perry has been given a free hand to promote his agency’s renewable energy mission, and he’s been doing that with bells on — at least, so far.
Photo (margins cropped): via IMEC.
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