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Houston lab's breakthrough light-harvesting processes near market readiness

The new process developed by Rice University researchers makes solar cells that are about 10 times more durable than traditional methods. Photos by Jeff Fitlow/Rice University

A groundbreaking Rice University lab has made further strides in its work to make harvesting light energy more efficient and stable.

Presented on the cover of a June issue of Science, a study from Rice engineer Aditya Mohite's lab uncovered a method to synthesize a high-efficiency perovskite solar cell, known as formamidinium lead iodide (FAPbI3), converting them into ultrastable high-quality photovoltaic films, according to a statement from Rice. Photovoltaic films convert sunlight into electricity.

The new process makes solar cells that are about 10 times more durable than traditional methods.

“Right now, we think that this is state of the art in terms of stability,” Mohite said in a statement. “Perovskite solar cells have the potential to revolutionize energy production, but achieving long-duration stability has been a significant challenge.”

The change come from "seasoning" the FAPbI3 with 2D halide perovskites crystals, which the Mohite lab also developed a breakthrough synthesis process for last year

The 2D perovskites helped make the FAPbI3 films more stable. The study showed that films with 2D perovskites deteriorated after two days of generating electricity, while those with 2D perovskites had not started to degrade after 20 days.

“FAPbI3 films templated with 2D crystals were higher quality, showing less internal disorder and exhibiting a stronger response to illumination, which translated as higher efficiency," Isaac Metcalf, a Rice materials science and nanoengineering graduate student and a lead author on the study, said in the statement.

Additionally, researchers say their findings could make developing light-harvesting technologies cheaper, and can also allow light-harvesting panels to be lighter weight and more flexible.

"Perovskites are soluble in solution, so you can take an ink of a perovskite precursor and spread it across a piece of glass, then heat it up and you have the absorber layer for a solar cell,” Metcalf said. “Since you don’t need very high temperatures ⎯ perovskite films can be processed at temperatures below 150 Celsius (302 Fahrenheit) ⎯ in theory that also means perovskite solar panels can be made on plastic or even flexible substrates, which could further reduce costs.”

Mohite adds this has major implications for the energy transition at large.

“If solar electricity doesn’t happen, none of the other processes that rely on green electrons from the grid, such as thermochemical or electrochemical processes for chemical manufacturing, will happen,” Mohite said. “Photovoltaics are absolutely critical.”

The Mohite lab's process for creating 2D perovskites of the ideal thickness and purity was published in Nature Synthesis last fall. At the time, Mohite said the crystals "hold the key to achieving commercially relevant stability for solar cells."

About a year ago, the lab also published its work on developing a scalable photoelectrochemical cell. The research broke records for its solar-to-hydrogen conversion efficiency rate.

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A View From HETI

Rice's Atin Pramanik and a team in Pulickel Ajayan's lab shared new findings that offer a sustainable alternative to lithium batteries by enhancing sodium and potassium ion storage. Photo by Jeff Fitlow/Courtesy Rice University

A new study by researchers from Rice University’s Department of Materials Science and NanoEngineering, Baylor University and the Indian Institute of Science Education and Research Thiruvananthapuram has introduced a solution that could help develop more affordable and sustainable sodium-ion batteries.

The findings were recently published in the journal Advanced Functional Materials.

The team worked with tiny cone- and disc-shaped carbon materials from oil and gas industry byproducts with a pure graphitic structure. The forms allow for more efficient energy storage with larger sodium and potassium ions, which is a challenge for anodes in battery research. Sodium and potassium are more widely available and cheaper than lithium.

“For years, we’ve known that sodium and potassium are attractive alternatives to lithium,” Pulickel Ajayan, the Benjamin M. and Mary Greenwood Anderson Professor of Engineering at Rice, said in a news release. “But the challenge has always been finding carbon-based anode materials that can store these larger ions efficiently.”

Lithium-ion batteries traditionally rely on graphite as an anode material. However, traditional graphite structures cannot efficiently store sodium or potassium energy, since the atoms are too big and interactions become too complex to slide in and out of graphite’s layers. The cone and disc structures “offer curvature and spacing that welcome sodium and potassium ions without the need for chemical doping (the process of intentionally adding small amounts of specific atoms or molecules to change its properties) or other artificial modifications,” according to the study.

“This is one of the first clear demonstrations of sodium-ion intercalation in pure graphitic materials with such stability,” Atin Pramanik, first author of the study and a postdoctoral associate in Ajayan’s lab, said in the release. “It challenges the belief that pure graphite can’t work with sodium.”

In lab tests, the carbon cones and discs stored about 230 milliamp-hours of charge per gram (mAh/g) by using sodium ions. They still held 151 mAh/g even after 2,000 fast charging cycles. They also worked with potassium-ion batteries.

“We believe this discovery opens up a new design space for battery anodes,” Ajayan added in the release. “Instead of changing the chemistry, we’re changing the shape, and that’s proving to be just as interesting.”

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