A new fabrication method has allowed researchers to make larger perovskite solar cells with few defects, helping to maintain efficiency at larger cell sizes. Image: Brown University/NREL.Using a newly-developed fabrication method, a research team has attained a greater than 15% energy conversion efficiency from perovskite solar cells larger than 1cm2. The researchers, from Brown University and the US National Renewable Energy Lab (NREL), report their findings in Advanced Materials.
Perovskites are crystalline materials that have caused quite a buzz in the solar energy world. Perovskite solar cells are relatively cheap to make, and the efficiency with which they can convert sunlight into electricity has been increasing rapidly in recent years. Researchers have reported efficiency in perovskite cells of higher than 20%, rivaling traditional silicon cells. Those high efficiency ratings, however, have so far been achieved using cells just 0.1cm2 in size – fine for laboratory testing, but too small to be used in a solar panel.
"The use of tiny cells for efficiency testing has prompted some to question comparisons of perovskite solar cells with other established photovoltaic technologies," said Nitin Padture, professor of engineering at Brown, director of Brown's Institute for Molecular and Nanoscale Innovation, and one of the senior authors of the new research. "But here we have shown that it is feasible to obtain 15% efficiency on cells larger than 1cm2 through improved processing. This is real progress."
Maintaining high efficiency on larger perovskite cells has proved to be a challenge, Padture says. "The problem with perovskite has been that when you try to make larger films using traditional methods, you get defects in the film that decrease efficiency."
The fabrication process that the researchers from Brown and NREL have now reported builds on a previously reported method developed by Yuanyuan Zhou, a graduate student in Padture's lab. This method involves dissolving perovskite precursors in a solvent and coating them onto a substrate, which is then bathed in a second solvent (called an anti-solvent) that selectively grabs the precursor-solvent and whisks it away. What's left is an ultra-smooth film of perovskite crystals.
In this new study, Zhou and Mengjin Yang, a postdoctoral researcher at NREL, developed a trick to grow the perovskite crystals to a larger size. The trick is to add an excess of organic precursor that ‘glues’ the small perovskite crystals and helps them merge into larger ones during a heat-treatment that also bakes away the excess precursor.
"The full coverage and uniformity over a large area come from the solvent method," Padture said. "Once we have that coverage, then we increase the size of the crystals. That gives us a film with fewer defects and higher efficiency." The 15% efficiency reached in this latest work is a good start, Padture said, but there's still room for improvement. Ultimately, he would like to reach 20–25% in large-area cells, and he thinks that goal could be within reach using this method or a similar one.
Padture and colleagues at the University of Nebraska-Lincoln were recently awarded a $4-million grant by the National Science Foundation to expand their perovskite research.
This story is adapted from material from Brown University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.