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DOE scientists' discovery may boost solar cells' energy output by up to 40%

In what is being called a "surprise discovery," researchers at the U.S. Department of Energy's Lawrence Berkeley National Laboratory have found they may be able to boost energy conversion rates in one type of solar module by as much as 40%.

The research was published in the peer-reviewed journal Nature Energy.

Using an atomic microscope, the researchers observed multifaceted surfaces like a gemstone in solar cells made with the mineral perovskite. Some of the grains, which were about 200 microns in width, had sharply formed multi-angled facets, while others were poorly formed. The poorly formed facets had energy conversion efficiencies approaching 31%, which beats today's top photovoltaic efficiency rates of 22%.

The top-performing facets of perovskite-based solar cells could hold the secret to highly efficient solar cells, "although more research is needed," according to the scientists from the Berkley Labs' Molecular Foundry and the Joint Center for Artificial Photosynthesis.

"If the material can be synthesized so that only very efficient facets develop, then we could see a big jump in the efficiency of perovskite solar cells," Sibel Leblebici, a researcher at the Molecular Foundry, said in a news release.

Berkley Lab

This atomic force microscopy image of the grainy surface of a perovskite solar cell reveals a new path to much greater efficiency. Individual grains are outlined in black, low-performing facets are red and high-performing facets are green. A big jump in efficiency could possibly be obtained if the material can be grown so that more high-performing facets develop.

Like organic solar cells made of carbon-based materials combined with various metals, perovskite cells are inexpensive and easy to fabricate, the researchers said.

The vast majority of solar modules being manufactured for rooftop and other use today have a light-conversion efficiency rating of 15% to 17%; the rating refers to the percentage of photons striking the modules that can be turned into electric current.

Even more interesting, the researchers added, is that the efficiency at which perovskite solar cells convert photons to electricity has increased more rapidly than any other material to date, starting with 3% in 2009 -- when research first began -- to 22% today. Twenty-two percent is roughly the same solar efficiency rate as crystalline silicon-based solar cells, which are, by far, the most prevalent material used to manufacture solar cells today.

MJ Shiao, director of solar research at GTM Research, explained that in large solar power systems, such as utility-scale power plants, photovoltaic modules make up over 50% of system costs and technology gains like improved efficiency can help reduce solar energy costs.

"However, it's difficult to bet against crystalline silicon technology in the next few years," Shiao said. "While developments in the lab can show a material's potential, the real challenge is driving commercial production at a high yield, low cost and with product reliability and corporate bankability that can match the 20- to 30-year asset life for a solar PV system."

Amit Ronen, director of George Washington University's Solar Institute, said perovskite-based solar cells are a "particularly promising technology that could one day generate much more electricity per photon than the silicon-based solar cells that dominate the marketplace today."

"However, economics drive solar uptake rates, not necessarily theoretical efficiency rates," Ronen said. "Perovskites have a long way to go before they can emerge from the lab bench to compete with hundreds of billions of dollars of silicon-based manufacturing capacity and a product that is already less expensive today than fossil fuel generation in most cases."

Ronen said that continued government funding of cutting edge research, like what Berkley Labs is doing, "is essential" to helping the private sector bring new innovations and breakthroughs to the marketplace "that can provide Americans with cheaper electricity and the world with cleaner power supplies."

"Opening up electricity markets to new entrants is also critical to getting perovskite-based cells to be part of our nation's mix," Ronen continued. "Even with today's solar cells outcompeting fossil fuels, a host of legal, regulatory, and technical hurdles continue to slow our urgently needed transition to a cleaner and more distributed energy system."

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