Researchers have actually utilized self-assembled monolayer “molecular glue” to strengthen user interfaces in perovskite solar batteries to make them more effective, steady, and trustworthy. Credit: Padture laboratory/Brown University
A research study group from Brown University has actually made a significant action towards enhancing the long-lasting dependability of perovskite solar batteries, an emerging tidy energy innovation. In a research study to be released on Friday, May 7, 2021, in the journal Science, the group shows a “molecular glue” that keeps an essential user interface inside cells from deteriorating. The treatment significantly increases cells’ stability and dependability gradually, while likewise enhancing the performance with which they transform sunshine into electrical energy.
“There have been great strides in increasing the power-conversion efficiency of perovskite solar cells,” stated Nitin Padture, a teacher of engineering at Brown University and senior author of the brand-new research study. “But the final hurdle to be cleared before the technology can be widely available is reliability — making cells that maintain their performance over time. That’s one of the things my research group has been working on, and we’re happy to report some important progress.”
Perovskites are a class of products with a specific crystalline atomic structure. A little over a years earlier, scientists revealed that perovskites are excellent at taking in light, which triggered a flood of brand-new research study into perovskite solar batteries. The performance of those cells has actually increased rapidly and now matches that of standard silicon cells. The distinction is that perovskite light absorbers can be made at near space temperature level, whereas silicon requires to be grown from a melt at a temperature level approaching 2,700 degrees Fahrenheit. Perovskite movies are likewise about 400 times thinner than silicon wafers. The relative ease of the production procedures and making use of less product implies perovskite cells can be possibly made at a portion of the expense of silicon cells.
While the performance enhancements in perovskites have actually been impressive, Padture states, making the cells more steady and trustworthy has actually stayed tough. Part of the issue pertains to the layering needed to make an operating cell. Each cell consists of 5 or more unique layers, each carrying out a various function in the electricity-generation procedure. Since these layers are made from various products, they react in a different way to external forces. Also, temperature level modifications that take place throughout the production procedure and throughout service can trigger some layers to broaden or contract more than others. That produces mechanical tensions at the layer user interfaces that can trigger the layers to decouple. If the user interfaces are jeopardized, the efficiency of the cell plummets.
The weakest of those user interfaces is the one in between the perovskite movie utilized to take in light and the electron transportation layer, which keeps existing streaming through the cell.
“A chain is only as strong as its weakest link, and we identified this interface as the weakest part of the whole stack, where failure is most likely,” stated Padture, who directs the Institute for Molecular and Nanoscale Innovation at Brown. “If we can strengthen that, then we can start making real improvements in reliability.”
To do that, Padture made use of his experience as a product researcher, establishing innovative ceramic finishes utilized in airplane engines and other high-performance applications. He and his associates started explore substances called self-assembled monolayers or SAMs.
“This is a large class of compounds,” Padture stated. “When you deposit these on a surface, the molecules assemble themselves in a single layer and stand up like short hairs. By using the right formulation, you can form strong bonds between these compounds and all kinds of different surfaces.”
Padture and his group discovered that a formula of SAM with silicon atom on one side, and iodine atom on the other, might form strong bonds with both the election transportation layer (which is typically made from tin oxide) and the perovskite light-absorbing layer. The group hoped that the bonds formed by these particles may strengthen the layer user interface. And they were right.
“When we introduced the SAMs to the interface, we found that it increases the fracture toughness of the interface by about 50%, meaning that any cracks that form at the interface tend not to propagate very far,” Padture stated. “So in effect, the SAMs become a kind of molecular glue that holds the two layers together.”
Testing of solar battery function revealed that the SAMs significantly increased the practical life of the perovskite cells. Non-SAM cells gotten ready for the research study maintained 80% of its preliminary performance for around 700 hours of laboratory screening. Meanwhile the SAM cells were still going strong after 1,330 hours of screening. Based on these experiments, the scientists forecast the 80%-retained-efficiency life to be about 4,000 hours.
“One of the other things we did, which people don’t normally do, is we broke open the cells after testing,” stated Zhenghong Dai, a Brown doctoral trainee and very first author of the research study. “In the control cells without the SAMs, we saw all kinds of damage such as voids and cracks. But with the SAMs, the toughened interfaces looked really good. It was a dramatic improvement that really kind of shocked us.”
Importantly, Padture stated, the enhancement in strength did not come at the expense of power-conversion performance. In reality, the SAMs in fact enhanced the cell’s performance by a percentage. That took place since the SAMs removed small molecular problems that form when the 2 layers bond in the lack of SAMs.
“The first rule in improving the mechanical integrity of functional devices is ‘do no harm,’” Padture stated. “So that we could improve reliability without losing efficiency — and even improving efficiency — was a nice surprise.”
The SAMs themselves are made from easily offered substances and are quickly used with a dip-coating procedure at space temperature level. So the addition of SAMs would possibly include little to the production expense, Padture stated.
The scientists prepare to construct on this success. Now that they’ve strengthened the weakest link in the perovskite solar battery stack, they’d like to move onto the next weakest, then the next and so on till they’ve strengthened the whole stack. That work will include reinforcing not just the user interfaces, however likewise the product layers themselves. Recently, Padture’s research study group won a $1.5 million grant from the U.S. Department of Energy to broaden on their research study.
“This is the kind of research that’s required in order to make cells that are inexpensive, efficient, and perform well for decades,” Padture stated.
Reference: 7 May 2021, Science.
DOI: 10.1126/science.abf5602
Srinivas K. Yadavalli, Min Chen, Ali Abbaspourtamijani and Yue Qi were co-authors of the research study, which was moneyed by the Office of Naval Research (N00014-17-1-2232 and N00014-20-1-2574) and the National Science Foundation (1538893 and 2002158).
