Iowa State engineers designed this proof-of-concept perovskite solar cell within their lab for research. Credit: Harshavardhan Gaonkar
Due to their crystal structure and electro-optical properties that are promising, Perovskites could be the key ingredient in future generations of cheap, efficient, light, and flexible solar cells.
The issue with the current technology of the silicon solar cell is its low efficiency in the conversion of solar energy into electricity, as per Vikram Dalal. She is the Iowa State University Anson Marston Distinguished Professor of Engineering, Thomas M. Whitney Professor in Electrical and Computer Engineering, and the Iowa State’s Microelectronics Research Center director.
The most efficient silicon solar cells in the lab are 26% efficient. Commercial cells are around 15 percent. The bigger the system, the more needed to produce a specific power, and bigger systems can mean higher prices.
Researchers are seeking new methods to increase efficiency and reduce costs. One possibility that could increase efficiency up to 50 percent is a tandem structure that layers two kinds of cells over one another, each using different and complementary components of the spectrum of solar energy to generate energy.
Perovskite promise, problems
Researchers are currently investigating hybrid organic-inorganic materials that could be a great companion for silicon cells. Perovskite cells are efficient to the tune of 25%, possess the benefit of a complementary bandgap, and are extremely thin (just one-millionth of a millimeter), and easily be placed on silicon.
However, Dalal claimed that researchers have discovered that these hybrid solar cells disintegrate when exposed to extreme temperatures.
This is a problem when installing solar panels where the sun is hot and deserts like those in American southwest Australia and Australia, the Middle East, and India. Temperatures in these regions can reach between 120 and 130 degrees Fahrenheit, while the solar cell’s temperature can exceed 200 degrees Fahrenheit.
As part of a project partly funded through the National Science Foundation, Iowa State University engineers have discovered a way to make use of the properties of perovskite while also stabilizing cells at high temperatures. They present their findings in a recent paper published in the journal who is the paper’s primary author. Gaonkar recently earned an engineering doctorate at Iowa State and is now working in Boise, Idaho, as an engineer for ON Semiconductor.
The material can be altered by tweaking it.
Dalal, the co-author of the research paper, stated two important innovations in the new technique for solar cells.
In the beginning, he stated that engineers tweaked the structure of the perovskite materials.
They removed organic elements in the material, particularly Cations, which have additional protons and positive charges, and replaced them with inorganic ones like cesium. The material was then solid at higher temperatures.
They also developed an elaboration technique that creates the perovskite material in a thin layer – one billionth of a millimeter at one time. The vapor deposition method is reliable, does not leave behind pollutants, and is employed in other industries, making it scalable to commercial production.
What is the result of these changes?
“Our perovskite solar cells show no thermal degradation even at 200 degrees Celsius (390 degrees Fahrenheit) for over three days, temperatures far significantly more than what the solar cell will have to endure in real-world environments,” Gaonkar stated.
Then Dalal conducted a bit of comparison and contrast: “That’s far better than organic perovskite-like cells which would have completely decomposed in this condition at the temperature. It’s a significant advancement within the science.”
The paper indicates that the new inorganic solar cells with a photoconversion efficiency of 11.8 percent. That means that there’s a lot of work to be done by engineers.
“We’re now trying to optimize this cell – we want to allow it to be more effective at converting solar energy into electricity,” Dalal stated. “We still have a lot of research to complete, but we think we can make it happen by utilizing new combinations of materials.”
The engineers, fol stated. “We still have lots of research to accomplish, but we think we could make it by utilizing new combinations of materials.”
The engineers, for instance, have replaced the iodine that is commonly found in perovskite material with bromine. This made the cells less susceptible to moisture, which solved another issue with conventional hybrid perovskites. But, the change in the cell’s properties reduced efficiency and the efficiency with which they function together to silicon-based cells.
So the tests and tweaks will continue.
While they’re moving forward with their research, they believe they’re on the right track: “This study demonstrates a better quality thermal stability of inorganic perovskite materials and solar cells at higher temperatures and over extended periods than reported elsewhere,” they said in their research paper. “(These are) promising results in the quest for the commercialization of perovskite solar panel materials..”
Reference: “Thermally Stable, Efficient, Vapor Deposited Inorganic Perovskite Solar Cells” by Harshavardhan Gaonkar, Junhao Zhu, Ranjith Kottokkaran, Behrang Bhageri Max Noack and Vikram Dalal, 23 March 2020, ACS Applied Energy Materials.
Alongside Vikram Dalal, Harshavardhan Gaonkar’s research team also includes Max Noack, associate scientist; Ranjith Kottokkaran, assistant scientist; Junhao Zhu and Behrang Bagheri as graduate students.