Indian American led team boosts ultrathin solar cells

Rice graduate student Wenbin Li, chemical and biomolecular engineer Aditya Mohite and graduate student Siraj Sidhik led the project to produce toughened 2D perovskites for efficient solar cells. (Rice News Photo)

Rice University professor Aditya Mohite ranked among the world’s highly cited researchers

Rice University engineers led by Indian American Aditya Mohite have with a new design boosted the efficiency of atomically thin solar cells made of semiconducting perovskites while still standing up to the environment.

Mohite’s lab at Rice’s George R. Brown School of Engineering discovered that sunlight itself contracts the space between atomic layers in 2D perovskites enough to improve the material’s photovoltaic efficiency by up to 18%, an astounding leap in a field where progress is often measured in fractions of a percent, according to Rice University press release.

“In 10 years, the efficiencies of perovskites have skyrocketed from about 3% to over 25%,” Mohite, an associate professor of chemical and biomolecular engineering and of materials science and nanoengineering, said. “Other semiconductors have taken about 60 years to get there. That’s why we’re so excited.”

Read: Indian American professor working to improve cancer treatment (November 2, 2021)

The research appears in Nature Nanotechnology.

Perovskites are compounds that have cube like crystal lattices and are highly efficient light harvesters. Their potential has been known for years, but they present a conundrum: They’re good at converting sunlight into energy, but sunlight and moisture degrade them.

“A solar cell technology is expected to work for 20 to 25 years,” said Mohite. “We’ve been working for many years and continue to work with bulk perovskites that are very efficient but not as stable.

“In contrast, 2D perovskites have tremendous stability but are not efficient enough to put on a roof,” he said. “The big issue has been to make them efficient without compromising the stability.”

The Rice engineers and their collaborators at Purdue and Northwestern universities, US Department of Energy national laboratories Los Alamos, Argonne and Brookhaven and the Institute of Electronics and Digital Technologies (INSA) in Rennes, France, discovered that in certain 2D perovskites, sunlight effectively shrinks the space between the atoms, improving their ability to carry a current.

“We find that as you light the material, you kind of squeeze it like a sponge and bring the layers together to enhance the charge transport in that direction,” Mohite said.

The researchers found placing a layer of organic cations between the iodide on top and lead on the bottom enhanced interactions between the layers.

“This work has significant implications for studying excited states and quasiparticles in which a positive charge lies on one layer and the negative charge lies on the other and they can talk to each other,” Mohite said. “These are called excitons, which may have unique properties.

“This effect has given us the opportunity to understand and tailor these fundamental light-matter interactions without creating complex heterostructures like stacked 2D transition metal dichalcogenides,” he said.

Experiments were confirmed by computer models by colleagues in France.

Both results showed that after 10 minutes under a solar simulator at one-sun intensity, the 2D perovskites contracted by 0.4% along their length and about 1% top to bottom. They demonstrated the effect can be seen in one minute under five-sun intensity.

“It doesn’t sound like a lot, but this 1% contraction in the lattice spacing induces a large enhancement of electron flow,” said Rice graduate student and co-lead author Wenbin Li. “Our research shows a threefold increase in the electron conduction of the material.”

At the same time, the nature of the lattice made the material less prone to degrading, even when heated to 80 degrees Celsius (176 degrees Fahrenheit). The researchers also found the lattice quickly relaxed back to its normal configuration once the light was turned off.

“One of the major attractions of 2D perovskites was they usually have organic atoms that act as barriers to humidity, are thermally stable and solve ion migration problems,” said graduate student and co-lead author Siraj Sidhik.

“3D perovskites are prone to heat and light instability, so researchers started putting 2D layers on top of bulk perovskites to see if they could get the best of both,” he said. “We thought, let’s just move to 2D only and make it efficient.”

To observe the material contraction in action, the team made use of two US Department of Energy (DOE) Office of Science user facilities: the National Synchrotron Light Source II at DOE’s Brookhaven National Laboratory and the Advanced Photon Source (APS) at DOE’s Argonne National Laboratory.

Meanwhile, Mohite has been ranked among the world’s highly cited researchers, according to a Rice University release.

Read: Rice University: Ultrathin Solar Cells Get A Boost (November 23, 2021)

The 2021 Highly Cited Researchers list is a global accounting of scientists who produced the last decade’s most influential papers, compiled by the Web of Science group, a Clarivate Analytics company.

The list recognizes researchers “who produced multiple papers ranking in the top 1% by citations for their field and year of publication, demonstrating significant research influence among their peers,” according to Web of Science.

It selected more than 6,600 researchers from 70 countries for their performance in 21 fields and for cross-field influence in scholarly publications.

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