Jul 27, 2019 | |
A good first step toward nontoxic solar cells(Nanowerk News) Solar panel installations are on the rise in the U.S., with more than 2 million new installations in early 2019, the most ever recorded in a first quarter. |
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To meet the ever-increasing demands, low-cost and more efficient alternatives to silicon-based solar cells — currently the most widely used technology — are desirable. In the past decade, lead-halide perovskites have surged as the most promising class of alternative materials; however, they are unstable. They contain lead, which is toxic and poses potential health and environmental hazards such as groundwater contamination. | |
A team of engineers at Washington University in St. Louis has found what they believe is a more stable, less toxic semiconductor for solar applications using a novel double perovskite oxide discovered through data analytics and quantum-mechanical calculations. | |
Their work was published in Chemistry of Materials ("KBaTeBiO6: A Lead-Free, Inorganic Double-Perovskite Semiconductor for Photovoltaic Applications"). | |
An atomic model of KBaTeBiO6 (left), the most promising of 30,000 oxides in a potential solar panel. At right is a scanning transmission electron micrograph showing the atomic structure of KBaTeBiO6, along with snapshot of the synthesized powder. (Image: Rohan Mishra) | |
Rohan Mishra, assistant professor of mechanical engineering & materials science in the McKelvey School of Engineering, led an interdisciplinary, international team that discovered the new semiconductor, made up of potassium, barium, tellurium, bismuth and oxygen (KBaTeBiO6). The lead-free double perovskite oxide was one of an initial 30,000 potential bismuth-based oxides. Of those 30,000, only about 25 were known compounds. | |
Using materials informatics and quantum mechanical calculations on one of the fastest supercomputers in the world, Arashdeep Singh Thind, a doctoral student in Mishra’s lab based at Oak Ridge National Laboratory, found KBaTeBiO6 to be the most promising out of the 30,000 potential oxides. | |
“We found that this looked to be the most stable compound and that it could be synthesized in the lab,” Mishra said. “More importantly, whereas most oxides tend to have a large band, we predicted the new compound to have a lower band gap, which is close to the halide perovskites, and to have reasonably good properties.” | |
The band gap is the energy barrier that electrons must overcome to form free carriers that, in the context of a solar cell, can be extracted to power an electrical device or stored in a battery for later use. The energy to overcome this barrier is provided by sunlight. The most promising compounds for solar cell applications have a band gap of about 1.5 eV, or electronvolt, Mishra said. | |
Mishra discussed the possibility of synthesizing KBaTeBiO6 with Pratim Biswas, assistant vice chancellor, the Lucy & Stanley Lopata Professor and chair of the Department of Energy, Environmental & Chemical Engineering. Shalinee Kavadiya, then a McKelvey Engineering doctoral student and now a postdoctoral research associate at Arizona State University, got to work on perfecting the recipe. | |
“Shalinee spent about six months synthesizing the material,” Mishra said. “Once she was able to synthesize it, as we had predicted, it was stable and had a band gap of 1.88 eV, which we also predicted.” | |
Mishra said these are first-generation solar cells that need more fine tuning of the band gap, but it is a good first step toward nontoxic solar cells. | |
“This shows that we can go away from these lead-halide perovskites,” Mishra said. “This opens up a really big space for designing semiconductors not just for solar cell applications but also for other semiconductor applications, such as LCD displays.” | |
Next, the team will study the role of any defects in this new semiconductor and look to more advanced synthesis techniques, including using aerosol techniques. |
Source: Washington University in St. Louis | |
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