How Low A Solar Cell Can Go, Perovskite Edition
The hits just keep on coming for fossil energy stakeholders, and the worst is yet to come as new low-cost perovskite solar cell technology bubbles up through the R&D pipeline. Helping things along is the US Department of Energy. The agency has spent years plotting the nation’s course back to a leadership role in the global solar industry, and they are counting on perovskites to carry the torch.
Winning The Global Perovskite Solar Cell Race…Eventually!
The Energy Department hopped on the perovskite train around 2009 and it has been plotting world domination nonstop ever since. The agency even kept up the momentum all through the previous four years, when official White House policy favored fossil fuels. It didn’t have a choice. The world keeps spinning no matter who occupies 1600 Pennsylvania Avenue, and researchers all over the world are hot on the trail of the perfect perovskite solar cell.
In one recent development, a team from the Okinawa Insitute of Science and Technology in Japan is on track to solve two key challenges for commercializing perovskite technology: perovskite solar cells tend to wilt in humidity, and they perform less efficiently as their size increases.
The humidity issue is solvable, and the OIST team pinpointed the source of the problem. As the team explains, nanoscale pinholes and defects are the culprits. They allow humidity and oxygen to seep into the solar cell, and the problem worsens as the size of the solar cell increases.
To correct all that, the OIST team decided to double the thickness of the layer that forms the heart of a typical perovskite solar cell. That’s easier said than done, and you can get all the juicy details about how they did it from the latest issue of the journal Advanced Energy Materials.
The shorter version is that they added ammonium chloride to the mixture used in growing the perovskite film, and then subtracted ammonia after the process was complete.
Here’s the rundown from the research team:
“Overall, the solar modules sized 5 x 5 cm2 showed an efficiency of 14.55%, up from 13.06% in modules made without ammonium chloride, and were able to work for 1600 hours – over two months – at more than 80% of this efficiency.
“The larger 10 x 10 cm2 modules had an efficiency of 10.25% and remained at high levels of efficiency for over 1100 hours, or almost 46 days.”
The project is still very much in the labwork phase, but the team is excited to note that their research demonstrated a first-of-its-kind lifespan achievement for a perovskite solar cell.
Next steps include switching fabrication methods and increasing the size of the solar cell while maintaining solar conversion efficiency.
Another Road To Low-Cost Solar
Another interesting development recently emerged from the National University of Science and Technology in Russia with an assist from the University of Tor Vergata in Italy.
The team modded out their perovskite solar cell with MXenes, a class of two-dimensional ceramics, in order to improve performance.
“The MXenes-based modified cells showed superior performance, with power conversion efficiency exceeding 19% (the reference demonstrated 17%) and improved stabilized power output with respect to reference devices,” the team reported.
Interesting! Not for nothing, but MXenes were discovered in 2011 by a research team at Drexel University, which soon sparked interest from the Energy Department.
In 2013 CleanTechnica took note of the potential impact of MXenes on the energy storage field, and by 2017 the Energy Department’s Oak Ridge National Laboratory was hammering away on the energy storage angle, too. The solar cell application is news to us, so stay tuned for more on that.
Why Is Everybody Talking About Perovskites?
Good question. The global solar industry has traveled far and wide on silicon-based technology, and there is still some room to cut costs and improve solar conversion efficiency.
However, silicon has been the go-to material for commercial solar cells ever since Bell Labs demonstrated the first practical PV device in 1954. That was 67 years ago. The mass market is long overdue for the Next Best Thing, the cheaper, lighter, and more flexible the better. Considering the urgency of climate action, the ability to step up the pace of manufacturing would be a plus, too.
That is where perovskites come in. A class of crystalline materials with superior optical qualities, perovskites first popped up on the PV research radar around 2006. They initially sported a lowly solar conversion efficiency of just 3%, but the rate of improvement has been speedy, and the Energy Department is banking on the potential for the learning curve to keep shooting upwards.
Perovskites can be grown synthetically at relatively low expense, compared to the cost of fabricating silicon. Also, a perovskite solution can be painted, printed, or sprayed on a surface to make a solar cell, which lowers the cost of manufacturing while speeding up the pace of production.
The solution-based element also means that perovskite solution can be applied to surfaces that are light, flexible, and/or irregularly shaped, which would provide for a far greater range of application.
US Eyeballs Leadership In Global Solar Field
The early Bell Labs research gave the US a jump on the global solar industry, and the US held a leading position for pretty much the rest of the 20th century. However, that was back when solar cell technology was expensive, and mainly confined to space applications.
By the time affordable silicon-based technology surged into the mass market, domestic solar cell manufacturers could not compete in the global arena. The notable exception that proves the rule is Washington-based First Solar. The company specializes in thin film CdTe (cadmium telluride) technology, which holds a small but significant share of the global market.
Thin film solar cells cost less to manufacture than conventional solar cells, so combine that idea with perovskites and you just might have a winning model for ramping up solar cell production in the US. That’s what the Energy Department seems to be banking on. The agency has set up a whole suite of initiatives to accelerate the advanced manufacturing trend, and it has been promoting perovskite technology as the doorway through which the US manufacturing sector can compete.
Who’s Gonna Clean Up This Mess?
If all goes according to plan, the next problem is what to do when millions of square feet of perovskite solar cell-coated surfaces reach the end of their useful life. Lifecycle issues are of particular concern due to the use of lead in the perovskite-growing formula.
Lead-absorbing coatings are among the measures that can prevent the risk of lead leaching out from a damaged solar cell while still in use, but that still leaves the problem of handling lead in solar cells that are being recycled.
A team of researchers based at the Hebrew University of Jerusalem in Israel is already on the case. Their solution is a screen-printed, triple-layer matrix of nanoparticles that frames the layer of perovskite film. The matrix enables somebody to come along and remove the perovskite layer without disturbing the rest of the solar cell, which could then be refurbished with a fresh layer of perovskite.
So far the team has demonstrated that the refurbished solar cell performs just as well as a new one. The next thing to wonder about is what to do with all that spent perovskite. If you have any thoughts about that, drop us a note in the comment thread.
Meanwhile, over here in the US the Energy Department’s National Renewable Energy Laboratory is behind yet another new development in perovskite solar cell technology, so stay tuned for more on that.
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Photo (cropped): Perovskite solar cell courtesy of Okinawa Institute of Science and Technology.
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