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Ultra-thin solar cells?

31 Dec, 2021

By hoppt

Ultra-thin solar cells

Ultra-thin solar cells?

Ultra-thin solar cells improved: 2D perovskite compounds have the suitable materials to challenge bulky products.

Engineers at Rice University have achieved new benchmarks in designing atomic-scale thin solar cells made of semiconductor perovskites, increasing their efficiency while maintaining their ability to withstand the environment.

The Aditya Mohite laboratory of Rice University's George R Brown School of Engineering found that sunlight shrinks the space between the atomic layers in a two-dimensional perovskite, enough to increase the photovoltaic efficiency of the material by as much as 18%, which is frequent progress. A fantastic leap has been achieved in the field and measured in percentages.

"In 10 years, the efficiency of perovskite has soared from about 3% to more than 25%," Mohite said. "Other semiconductors will take about 60 years to achieve. That's why we are so excited."

Perovskite is a compound with a cubic lattice and is an efficient light collector. Their potential has been known for many years, but they have a problem: They can convert sunlight into energy, but sunlight and moisture can degrade them.

"Solar cell technology is expected to last 20 to 25 years," said Mohite, associate professor of chemical and biomolecular engineering and materials science and nanoengineering. "We have been working for many years and continue to use large perovskites that are very effective but not very stable. In contrast, two-dimensional perovskites have excellent stability but are not efficient enough to be placed on the roof.

"The biggest problem is to make them efficient without compromising stability."
The Rice engineers and their collaborators from Purdue University and Northwestern University, Los Alamos, Argonne and Brookhaven of the US Department of Energy National Laboratory, and the Institute of Electronics and Digital Technology (INSA) in Rennes, France, and their collaborators found that In some two-dimensional perovskites, sunlight effectively shrinks the space between atoms, increasing their ability to carry electrical current.

"We found that when you ignite the material, you squeeze it like a sponge and gather the layers together to enhance the charge transfer in that direction," Mocht said. The researchers found that placing a layer of organic cations between the iodide on the top and the lead on the bottom can enhance the interaction between the layers.

"This work is of great significance to the study of excited states and quasiparticles, where one layer of positive charge is on the other, and the negative charge is on the other, and they can talk to each other," Mocht said. "These are called excitons, and they may have unique properties.

"This effect allows us to understand and adjust these basic light-matter interactions without creating complex heterostructures such as stacked 2D transition metal dichalcogenides," he said.

Colleagues in France confirmed the experiment with a computer model. Jacky Even, Professor of Physics at INSA, said: "This research provides a unique opportunity to combine the most advanced ab initio simulation technology, material research using large-scale national synchrotron facilities, and in-situ characterization of solar cells in operation. Combine." "This paper describes for the first time how the seepage phenomenon suddenly releases the charging current in the perovskite material."

Both results show that after 10 minutes of exposure to the solar simulator at a solar intensity, the two-dimensional perovskite shrinks by 0.4% along its length and about 1% from top to bottom. They proved that the effect could be seen within 1 minute under five sun intensities.

"It doesn't sound like much, but a 1% shrinkage of the lattice spacing will cause a substantial increase in electron flow," said Li Wenbin, a graduate student in Rice and co-lead author. "Our research shows that the electronic conduction of the material has increased threefold."

At the same time, the nature of the crystal lattice makes the material resistant to degradation, even when heated to 80 degrees Celsius (176 degrees Fahrenheit). The researchers also found that the lattice quickly relaxes back to its standard configuration once the lights are turned off.

"One of the main attractions of 2D perovskites is that they usually have organic atoms that act as humidity barriers, are thermally stable, and solve ion migration problems," said graduate student and co-lead author Siraj Sidhik. "3D perovskites are prone to thermal and light instability, so researchers started putting 2D layers on top of massive perovskites to see if they could make the most of both.

"We think, let's just switch to 2D and make it efficient," he said.

To observe the shrinkage of the material, the team used two user facilities of the US Department of Energy (DOE) Office of Science: the National Synchrotron Light Source II of the Brookhaven National Laboratory of the US Department of Energy and the Advanced State Laboratory of the US Department of Energy's Argonne National Laboratory. Photon Source (APS) Laboratory.

Argonne physicist Joe Strzalka, the paper's co-author, uses APS's ultra-bright X-rays to capture small structural changes in materials in real-time. The sensitive instrument at the 8-ID-E of the APS beamline allows for "operational" studies, which means studies conducted when the equipment undergoes controlled changes in temperature or environment under normal operating conditions. In this case, Strzalka and his colleagues exposed the photosensitive material in the solar cell to simulated sunlight while keeping the temperature constant and observed tiny contractions at the atomic level.

As a control experiment, Strzalka and his co-authors kept the room dark, increased the temperature, and observed the opposite effect—material expansion. This suggests that the light itself, not the heat it generates, caused the transformation.

"For such changes, it is important to conduct operational research," Strzalka said. "Just like your mechanic wants to run your engine to see what's going on in it, we essentially want to take a video of this conversion, not a single snapshot. Facilities such as APS allow us to do this."

Strzalka pointed out that APS is undergoing a significant upgrade to increase the brightness of its X-rays by up to 500 times. He said that when it is completed, brighter beams and faster, sharper detectors will increase the ability of scientists to detect these changes with greater sensitivity.

This can help the Rice team adjust the material for better performance. "We are designing cations and interfaces to achieve efficiencies of more than 20%," Sidhik said. "This will change everything in the perovskite field because then people will start to use 2D perovskite for 2D perovskite/silicon and 2D/3D perovskite series, which can bring the efficiency close to 30%. This will make Its commercialization is attractive."

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