October 19th, 2020 by Tina Casey
Election business is dominating the headlines over here in the US, but somehow the Department of Energy snuck in two pieces of news that squeeze more breath out of the nation’s beleaguered coal industry. The agency issued a new report that touts the benefits of oil and gas while leaving coal outside in the rain, and new research from an Energy Department laboratory indicates that next-generation perovskite solar cells could be far less expensive, and far more efficient, than any other PV currently available today.
Everybody Hates Coal
The timing of that new oil and gas report is especially interesting, considering that The New York Times also piled onto coal earlier this month with a new long-form article describing just how far the coal industry has declined during the Trump* administration, despite all those promises about saving coal jobs.
Wouldn’t this be a good time to rush to the defense of coal jobs instead of cheerleading for oil and gas? Just asking! After all, low cost natural gas has been the main force driving coal out of the power generation market.
Nevertheless, the Energy Department seems content to let gas push coal out of the picture.
“Not only is natural gas the largest contributor to the Nation’s electric power generation, but oil and natural gas combined are revitalizing the U.S. petrochemical manufacturing industry, supplying high-tech materials, increasing commerce from exporting liquefied natural gas, supporting renewable energy, and creating well-paying jobs across the country,” DOE explains.
Perovskite Solar Cells Aim Dagger At Heart Of Natural Gas
The Energy Department’s rosy outlook for oil and gas brushes off a rapidly accelerating trend, in which low cost renewable energy gives both coal and natural gas a run for the money in the power generation sector.
That’s where the new next-generation solar cells come in.
To be clear, silicon is still the gold standard for solar cell efficiency, and the cost of silicon solar cell costs has been spiraling downward. However, the cost of solar power is still a turnoff for many consumers. If a less pricey photovoltaic alternative could materialize, the pace of the renewable energy transition would pick up considerably.
With that in mind, the Energy Department is betting the ranch on a class of synthetic crystalline materials called perovskites. To support its case, the agency regularly cites the trajectory of perovskite solar cell efficiency improvements in the past few years. Serious research into perovskite solar cells began in 2009 at just 3% conversion efficiency, and now the latest perovskite PV iteration clocks in at 25%.
Eleven years is just the wink of an eye in the field of solar cell research. For context, consider that the first commercial silicon PV device was developed by Bell Labs with a conversion efficiency of 6% all the way back in 1954. Now here it is more than 60 years later, and commercial silicon has barely scraped into the 25% range.
High-Performance Perovskite PV On The Way
For those of you new to the topic, solar conversion efficiency is a way of measuring how good a solar cell is at converting light into electricity. The 100% mark is pretty much out of the question, but researchers have calculated that silicon PV maxes out at around 30%.
Conversion efficiency can bump up if other materials are added to the PV mix, but all else being equal, that means the cost bumps up, too.
Perovskites can shave some of the cost burden off the equation, and with that in mind let’s take a look at the latest news from the Energy Department’s Oak Ridge National Laboratory in Tennessee.
In a team effort with the University of Tennessee, Knoxville, ORNL spearheaded a new perovskite PV study that shines a light, so to speak, on a new pathway for improving perovskite solar cell efficiency.
“The discovery could improve novel hot-carrier solar cells, which convert sunlight to electricity more efficiently than conventional solar cells by harnessing photogenerated charge carriers before they lose energy to heat,” ORNL enthused in a press release last week.
The idea is to prevent the solar cell from wasting energy in the form of heat, as ORNL explains:
“When sunlight strikes a solar cell, photons create charge carriers — electrons and holes — in an absorber material. Hot-carrier solar cells quickly convert the energy of the charge carriers to electricity before it is lost as waste heat. Preventing heat loss is a grand challenge for these solar cells, which have the potential to be twice as efficient as conventional solar cells.”
“The conversion efficiency of conventional perovskite solar cells has improved from 3% in 2009 to more than 25% in 2020. A well-designed hot-carrier device could achieve a theoretical conversion efficiency approaching 66%,” the lab adds.
The basic idea is to reduce swaying in the solar material by removing hydrogen. That enables the calmed-down material to interact with vibrations that would otherwise remove heat.
For all the juicy details, check out the team’s study under the somewhat intimidating title, “Giant isotope effect on phonon dispersion and thermal conductivity in methylammonium lead iodide,” in the journal Science Advances.
Everybody Loves Perovskite Solar Cells
The Energy Department brought in the heavy artillery to support the ORNL effort. The agency’s Office of Science chipped in for the research along with the Vehicle Technology Office from the Office of Energy Efficiency and Renewable Energy, and so did the US Department of Homeland Security.
Wait — DHS? If you have any ideas on that angle, drop a note in the comment thread.
The Office of Science is billed as the “single largest supporter of basic research in the physical sciences in the United States,” but that’s just the tip of the iceberg of forces arrayed in support of perovskite solar cells.
Last spring the Energy Department’s National Renewable Energy Laboratory launched a new consortium aimed at staking out the pole position for the US in the global PV market.
The executive board of the so-named US Manufacturing of Advanced Perovskites Consortium (US-MAP) is spearheaded by NREL and joined by the Washington Clean Energy Testbeds at the University of Washington, the University of North Carolina at Chapel Hill, and the University of Toledo.
On the industry side, NREL has recruited an advisory board consisting of the US companies BlueDot Photonics, Energy Materials Corporation, First Solar, Hunt Perovskites Technologies, Swift Solar, and Tandem PV.
The University of Colorado at Boulder and the SLAC National Accelerator Laboratory are also on board, and US-MAP is probably eyeballing the potential to expand its network as we speak.
On Beyond Solar
Aside from solar energy applications, NREL points out that “perovskites have shown tremendous promise in a range of other technologies, including solid-state lighting, advanced radiation detection, dynamic sensing and actuation, photo-catalysis, and quantum information science.”
Tooting its own horn, NREL credits the Energy Department’s Solar Energy Technologies Office and Office of Science with supporting early-stage research that has stimulated a rich trove of perovskite expertise in the domestic sphere.
The new consortium will coordinate efforts to ensure that perovskite solar materials make it out of the lab and onto the shelves of your local hardware store.
“While perovskite cells have shown promise in the lab, more work remains to be done to ensure that the technology is ready for commercial success. Manufacturing, durability, and sustainability remain challenges and will be the consortium’s research focus,” NREL explains. “Members of US-MAP will share research and development, validation, and pilot manufacturing, which will reduce development costs and technology risks for potential investors.”
That sound you hear is the collapse of the US coal industry, to be followed shortly by oil and gas.
Condolences to the family and friends of ORNL engineer William Collier, who passed away last week after becoming infected with the COVID-19 virus.
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Image: “Substituting deuterium for hydrogen makes methylammonium heavier and slows its swaying so it can interact with vibrations that remove heat, keeping charge carriers hot longer” (credit: Jill Hemman/ORNL, U.S. Dept. of Energy).
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