New Perovskite Solar Cells: How Low (And How Fast) Can Solar Go?
The cost of solar power has been dropping like a rock, and apparently we ain’t seen nothing yet. New low-cost perovskite solar cells are finally beginning to bump their way into the solar market. One promising pathway involves a piggyback with silicon technology, and thin film is also in play.
“Transformational” Perovskite Solar Cells Are Coming
Researchers at the US Department of Energy’s National Renewable Energy Laboratory (NREL) have been cheerleading for perovskite solar cells, and with good reason. Perovskite is a mineral with superior optical properties, and synthetic variations can be lab-grown at relatively low cost (more details here).
There being no such thing as a free lunch, synthetic perovskites require some tweaking before they can beat silicon solar cells to the clean power punch.
“Perovskite materials offer excellent light absorption, charge-carrier mobilities, and lifetimes, resulting in high device efficiencies with opportunities to realize a low-cost, industry-scalable technology,” NREL enthuses, while cautioning that “[a]chieving this potential will require us to overcome barriers related to stability and environmental compatibility.”
If those kinks can be worked out, perovskite solar cells will have “transformational potential for rapid terawatt-scale solar deployment,” NREL added.
If You Can’t Beat ‘Em, Join ‘Em
The rap on perovskite solar cells used to be their fragility and relatively low solar conversion efficiency. There are different ways to resolve those issues, and one of them involves combining perovskite solar cells with silicon. The tandem relationship is mutual, with silicon providing the stability and perovskites kicking up overall solar cell efficiency without adding excess expense.
NREL is a longtime fan of perovskites and the lab has picked up on the tandem perovskite-silicon angle. In 2020, NREL took note of the potential for boosting the efficiency and reducing the cost of silicon solar cells by adding perovskites. They achieved a conversion efficiency of 27% with their perovskite-silicon solar cell, compared to just 21% for a silicon-only version.
The South Korean firm Qcells (an offshoot of Hanwha Solutions) has also gotten the memo, and the company is taking it on the road. On May 17, Qcells announced that it has invested a cool $100 million in a pilot line to bring tandem perovskite cells with silicon to market.
“The investment will pave the way for Qcells to mass-produce perovskite tandem cells, which have a much higher efficiency rate than silicon-based solar cells that utilize TOPCon (Tunnel Oxide Passivated Contact) or heterojunction technology,” Qcells explained.
Don’t just take their word for it. Earlier this year, NREL verified a solar conversion efficiency rate of up to 29.3% for the tandem perovskite-silicon solar cell developed by Qcells and its research partners in Germany. That surpasses the theoretical maximum of 29.1% for silicon-only solar cells.
Hanwha will host the new tandem line at its Jincheon factory in South Korea, and it is not letting the grass grow under its feet. The line should be up and running by late 2024, with commercialization expected 2026.
The Perovskite Solar Cell Game Is Afoot
That’s just the tip of the perovskite-silicon iceberg. Qcells is part of a European tandem solar cell commercialization project called PEPPERONI, which currently includes 17 partners from 12 different European countries. Korea also has a foot in the door by way of the Qcells team in Germany, which is hosting the PEPPERONI project at its facility in Thalheim.
PEPPERONI launched in November last year, and that may have caught the eye of the US company First Solar, which has been scouting for opportunities to boost the conversion efficiency of its thin-film solar technology.
Thin-film technology can’t match the solar conversion efficiency of conventional silicon solar cells, but it does have two advantages. Thin-film solar cells lend themselves to rapid, high-volume, low-cost manufacturing processes, and they are lightweight and flexible, which means they have a far greater range of application.
Perovskites could help narrow the conversion gap for thin film. That may be what First Solar had up its sleeve when it recently acquired the Swedish perovskite startup Evolar AB (more First Solar coverage here). The deal is a two-phase arrangement, with the second phase depending on technology advancements, so stay tuned for more on that.
Perovskite Solar Cells, Thin-Film Edition
First Solar’s thin-film formula is based on cadmium telluride solar cell technology, or CdTe for short, which the company describes as “lower cost, superior scalability, and a higher theoretical efficiency limit” than conventional silicon solar cells, along with a laundry list of other advantages.
The company is still tweaking its formula, and its website currently anticipates achieving 25% solar conversion efficiency by 2025, with 28% in the company’s sights by 2030.
Perovskite solar cells could boost First Solar ahead of those goals. Back in 2019, a team of researchers at the University of Texas at Austin and Colorado State University made the case for adding perovskites to thin-film CdTe solar cells. They indicated that the perovskite formula of methylammonium-lead-bromide would be a good candidate, partly because it is amenable to energy-efficient, low-temperature fabrication.
“The approach of increasing CdTe PV efficiency by the addition of a wide bandgap perovskite layer in a 4T tandem device configuration appears to be a plausible way to increase efficiency without significantly increasing manufacturing cost,” they concluded.
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Many Paths To A Perovskite Future
The tandem approach is just one angle on the potential for next-generation perovskite technology to keep driving the cost of solar power down. Another angle involves eliminating the need to use an expensive gold anode to juice the performance of perovskite solar cells.
A research team in China has just published a study that indicates how a buffer layer can prevent a low-cost carbon paste anode from corroding the perovskite. They reached a conversion rate of 20.8% for their new carbon-perovskite solar cell. That doesn’t hit the high mark set by perovskite-silicon solar cells, but it does offer a pathway towards driving down the cost of reasonably efficient, affordable solar technology.
In another cost-cutting development for solar power, earlier this year, NREL introduced a self-assembling formula for trimming down the number of heating and coating steps needed to fabricate perovskite solar cells. Xiaopeng Zheng, a postdoctoral researcher in the Chemistry and Nanoscience Center at NREL, estimates that the process could be cut down by one-third.
Those of you following the perovskite saga may also be wondering whatever happened to the firm Oxford PV. The Oxford University spinoff first sailed across the CleanTechnica radar about 10 years ago with a perovskite-silicon solar cell (complete covereage here). It’s been a long journey, but it looks like all that hard work is about to pay off. Earlier this year, Reuters reported that Oxford PV’s tandem solar cells are expected to launch on the market sometime this year, sporting a conversion efficiency of 27%.
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Photo: Fabricating solar cells with perovskites, courtesy of Qcells.
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