Molecular Glue Perovskite Solar Cells

“Molecular Glue” Boosts Effectivity and Makes Perovskite Photo voltaic Cells Dramatically Extra Dependable Over Time

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, steady, and dependable. Credit score: Padture lab/Brown College

A analysis crew 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, Might 7, 2021, within the journal Science, the crew demonstrates a “molecular glue” that retains a key interface inside cells from degrading. The therapy 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 growing the power-conversion effectivity of perovskite photo voltaic cells,” stated 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 will be broadly obtainable is reliability — making cells that keep their efficiency over time. That’s one of many issues my analysis group has been engaged on, and we’re pleased to report some vital progress.”

Perovskites are a category of supplies with a selected crystalline atomic construction. Slightly over a decade in the past, researchers confirmed that perovskites are superb 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 will 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 using much less materials means perovskite cells will 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 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 special perform within the electricity-generation course of. Since these layers are constructed from totally different supplies, they reply in a different way to exterior forces. Additionally, temperature adjustments that happen in the course of the manufacturing course of and through service could cause some layers to broaden 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 simply as sturdy as its weakest hyperlink, and we recognized this interface because the weakest a part of the entire stack, the place failure is probably,” 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 fabric scientist, growing 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 massive class of compounds,” Padture stated. “Once you deposit these on a floor, the molecules assemble themselves in a single layer and rise up like quick hairs. By utilizing the best formulation, you possibly can type sturdy bonds between these compounds and every kind of various surfaces.”

Padture and his crew discovered {that a} formulation of SAM with silicon atom on one facet, and iodine atom on the opposite, might type sturdy bonds with each the election transport layer (which is often made from tin oxide) and the perovskite light-absorbing layer. The crew hoped that the bonds shaped by these molecules would possibly fortify the layer interface. They usually have 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%, that means that any cracks that type on the interface have a tendency to not propagate very far,” Padture stated. “So in impact, the SAMs develop into a form of molecular glue that holds the 2 layers collectively.”

Testing of photo voltaic cell perform confirmed that the SAMs dramatically elevated the useful 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 have been nonetheless going sturdy after 1,330 hours of testing. Based mostly on these experiments, the researchers mission 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 creator of the analysis. “Within the management cells with out the SAMs, we noticed every kind of harm comparable 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 stated, the advance in toughness didn’t come at the price of power-conversion effectivity. In reality, 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 enhancing the mechanical integrity of useful units is ‘do no hurt,’” Padture stated. “In order that we might enhance reliability with out shedding effectivity — and even enhancing effectivity — was a pleasant shock.”

The SAMs themselves are constructed from 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 value, 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 subsequent weakest, then the subsequent and so forth 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 broaden on their analysis.

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

Reference: 7 Might 2021, Science.
DOI: 10.1126/science.abf5602

Srinivas Ok. Yadavalli, Min Chen, Ali Abbaspourtamijani and Yue Qi have 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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