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“Molecular Glue” Boosts Efficiency and Makes Perovskite Solar Cells Dramatically More Reliable Over Time

Researchers have used self-assembled monolayer “molecular glue” to toughen interfaces in perovskite photo voltaic cells to make them extra environment friendly, steady, and dependable. Credit score: Padture lab/Brown College

A analysis workforce from Brown College has made a serious step towards bettering the long-term reliability of perovskite photo voltaic cells, an rising clear power expertise. In a research to be printed on Friday, Could 7, 2021, within the journal Science, the workforce demonstrates a “molecular glue” that retains a key interface inside cells from degrading. The remedy dramatically will increase cells’ stability and reliability over time, whereas additionally bettering the effectivity with which they convert daylight into electrical energy.

“There have been nice strides in rising the power-conversion effectivity of perovskite photo voltaic cells,” mentioned Nitin Padture, a professor of engineering at Brown College and senior creator of the brand new analysis. “However the last hurdle to be cleared earlier than the expertise might be extensively out there is reliability — making cells that preserve their efficiency over time. That’s one of many issues my analysis group has been engaged on, and we’re pleased to report some necessary progress.”

Perovskites are a category of supplies with a selected crystalline atomic construction. Just a little over a decade in the past, researchers confirmed that perovskites are excellent at absorbing mild, which set off a flood of latest analysis into perovskite photo voltaic cells. The effectivity of these cells has elevated rapidly and now rivals that of conventional silicon cells. The distinction is that perovskite mild absorbers might be made at close to room temperature, whereas silicon must be grown from a soften at a temperature approaching 2,700 levels Fahrenheit. Perovskite movies are additionally about 400 instances thinner than silicon wafers. The relative ease of the manufacturing processes and using much less materials means perovskite cells might be doubtlessly made at a fraction of the price of silicon cells.

Whereas the effectivity enhancements in perovskites have been outstanding, Padture says, making the cells extra steady and dependable has remained difficult. A part of the issue has to do with the layering required to make a functioning cell. Every cell incorporates 5 or extra distinct layers, every performing a distinct operate within the electricity-generation course of. Since these layers are made out of totally different supplies, they reply in another way to exterior forces. Additionally, temperature modifications that happen through the manufacturing course of and throughout service may cause some layers to develop or contract greater than others. That creates mechanical stresses on the layer interfaces that may trigger the layers to decouple. If the interfaces are compromised, the efficiency of the cell plummets.

The weakest of these interfaces is the one between the perovskite movie used to soak up mild and the electron transport layer, which retains present flowing by way of the cell.

“A series is barely as robust as its weakest hyperlink, and we recognized this interface because the weakest a part of the entire stack, the place failure is most certainly,” mentioned Padture, who directs the Institute for Molecular and Nanoscale Innovation at Brown. “If we will strengthen that, then we will begin making actual enhancements in reliability.”

To do this, Padture drew on his expertise as a cloth scientist, creating superior ceramic coatings utilized in plane engines and different high-performance functions. He and his colleagues started experimenting with compounds often called self-assembled monolayers or SAMs.

“This can be a giant class of compounds,” Padture mentioned. “While you deposit these on a floor, the molecules assemble themselves in a single layer and rise up like quick hairs. Through the use of the precise formulation, you possibly can type robust bonds between these compounds and all types of various surfaces.”

Padture and his workforce discovered {that a} formulation of SAM with silicon atom on one facet, and iodine atom on the opposite, may type robust bonds with each the election transport layer (which is often product of tin oxide) and the perovskite light-absorbing layer. The workforce hoped that the bonds shaped by these molecules may fortify the layer interface. They usually had been proper.

“Once we launched the SAMs to the interface, we discovered that it will increase the fracture toughness of the interface by about 50%, which means that any cracks that type on the interface have a tendency to not propagate very far,” Padture mentioned. “So in impact, the SAMs turn out to be a form of molecular glue that holds the 2 layers collectively.”

Testing of photo voltaic cell operate confirmed that the SAMs dramatically elevated the purposeful lifetime of the perovskite cells. Non-SAM cells ready for the research retained 80% of its preliminary effectivity for round 700 hours of lab testing. In the meantime the SAM cells had been nonetheless going robust after 1,330 hours of testing. Primarily based on these experiments, the researchers venture the 80%-retained-efficiency life to be about 4,000 hours.

“One of many different issues we did, which individuals don’t usually do, is we broke open the cells after testing,” mentioned Zhenghong Dai, a Brown doctoral pupil and first creator of the analysis. “Within the management cells with out the SAMs, we noticed all types of injury corresponding to voids and cracks. However with the SAMs, the toughened interfaces appeared actually good. It was a dramatic enchancment that actually form of shocked us.”

Importantly, Padture mentioned, the development in toughness didn’t come at the price of power-conversion effectivity. The truth is, the SAMs really improved the cell’s effectivity by a small quantity. That occurred as a result of the SAMs eradicated tiny molecular defects that type when the 2 layers bond within the absence of SAMs.

“The primary rule in bettering the mechanical integrity of purposeful gadgets is ‘do no hurt,’” Padture mentioned. “In order that we may enhance reliability with out dropping effectivity — and even bettering effectivity — was a pleasant shock.”

The SAMs themselves are made out of available compounds and are simply utilized with a dip-coating course of at room temperature. So the addition of SAMs would doubtlessly add little to the manufacturing price, Padture mentioned.

The researchers plan to construct on this success. Now that they’ve fortified the weakest hyperlink within the perovskite photo voltaic cell stack, they’d like to maneuver onto the subsequent weakest, then the subsequent and so on till they’ve fortified your complete stack. That work will contain strengthening not solely the interfaces, but additionally the fabric layers themselves. Lately, Padture’s analysis group gained a $1.5 million grant from the U.S. Division of Power to develop on their analysis.

“That is the form of analysis that’s required in an effort to make cells which are cheap, environment friendly, and carry out nicely for many years,” Padture mentioned.

Reference: “Interfacial toughening with self-assembled monolayers enhances perovskite photo voltaic cell reliability” by Zhenghong Dai, Srinivas Ok. Yadavalli, Min Chen, Ali Abbaspourtamijani, Yue Qi and Nitin P. Padture, 7 Could 2021, Science.
DOI: 10.1126/science.abf5602

Srinivas Ok. Yadavalli, Min Chen, Ali Abbaspourtamijani and Yue Qi had been co-authors of the analysis, which was funded by the Workplace of Naval Analysis (N00014-17-1-2232 and N00014-20-1-2574) and the Nationwide Science Basis (1538893 and 2002158).

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