Molecular Glue Perovskite Solar Cells

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

A analysis group from Brown College has made a significant step towards enhancing the long-term reliability of perovskite photo voltaic cells, an rising clear power expertise. In a research to be revealed on Friday, Could 7, 2021, within the journal Science, the group 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 enhancing 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,” stated Nitin Padture, a professor of engineering at Brown College and senior writer of the brand new analysis. “However the ultimate hurdle to be cleared earlier than the expertise could 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 blissful to report some essential progress.”

Perovskites are a category of supplies with a selected crystalline atomic construction. A bit over a decade in the past, researchers confirmed that perovskites are excellent at absorbing mild, which set off a flood of recent analysis into perovskite photo voltaic cells. The effectivity of these cells has elevated shortly and now rivals that of conventional silicon cells. The distinction is that perovskite mild absorbers could 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 occasions thinner than silicon wafers. The relative ease of the manufacturing processes and the usage of much less materials means perovskite cells could be probably 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 secure 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 constituted of totally different supplies, they reply in another way to exterior forces. Additionally, temperature modifications that happen throughout the manufacturing course of and through 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 means of the cell.

“A series is just as robust as its weakest hyperlink, and we recognized this interface because the weakest a part of the entire stack, the place failure is almost certainly,” stated 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 generally known as self-assembled monolayers or SAMs.

“It is a giant class of compounds,” Padture stated. “While you deposit these on a floor, the molecules assemble themselves in a single layer and get up like quick hairs. Through the use of the proper formulation, you possibly can kind robust bonds between these compounds and all types of various surfaces.”

Padture and his group discovered {that a} formulation of SAM with silicon atom on one aspect, and iodine atom on the opposite, might kind robust bonds with each the election transport layer (which is often fabricated from tin oxide) and the perovskite light-absorbing layer. The group hoped that the bonds shaped by these molecules would possibly fortify the layer interface. And so they had been proper.

“After 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 kind on the interface have a tendency to not propagate very far,” Padture stated. “So in impact, the SAMs change into 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 undertaking 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,” stated Zhenghong Dai, a Brown doctoral pupil and first writer of the analysis. “Within the management cells with out the SAMs, we noticed all types of harm reminiscent of voids and cracks. However with the SAMs, the toughened interfaces appeared actually good. It was a dramatic enchancment that basically form of shocked us.”

Importantly, Padture stated, the advance in toughness didn’t come at the price of power-conversion effectivity. Actually, the SAMs truly improved the cell’s effectivity by a small quantity. That occurred as a result of the SAMs eradicated tiny molecular defects that kind when the 2 layers bond within the absence of SAMs.

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

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

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 following weakest, then the following and so forth till they’ve fortified the complete stack. That work will contain strengthening not solely the interfaces, but in addition the fabric layers themselves. Just lately, Padture’s analysis group gained a $1.5 million grant from the U.S. Division of Vitality to develop on their analysis.

“That is the form of analysis that’s required with the intention to make cells which might be cheap, environment friendly, and carry out effectively for many years,” Padture stated.

Reference: 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).

By Rana

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