Rice Lab discovers 2D perovskite compound has what it takes to challenge bulkier products.
Rice University engineers have set a new benchmark in the design of atomically thin solar cells made from semiconductor perovskites, increasing their efficiency while maintaining their ability to withstand the environment.
Aditya Mohite’s lab at the George R. Brown School of Engineering in Rice discovered that sunlight itself sufficiently contracts the space between atomic layers in 2D perovskites to improve the photovoltaic efficiency of the material up to at 18%, an incredible leap in an area where progress is often measured in fractions of a percent.
“In 10 years, the effectiveness of perovskites has increased from around 3% to over 25%,” Mohite said. “Other semiconductors took about 60 years to get there. This is why we are so excited.
The search appears in Nature Nanotechnology.
Perovskites are compounds that have cubic crystal lattices and are very efficient light collectors. Their potential has been known for years, but they present a conundrum: They are good at converting sunlight into energy, but sunlight and humidity degrade them.
“A solar cell technology is expected to work for 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 work with bulk perovskites which are very effective but not as stable. In contrast, 2D perovskites have enormous stability but are not efficient enough to be placed on a roof.
“The big problem has been to make them effective without compromising stability,” he said.
Engineers Rice and their collaborators at Purdue and Northwestern Universities, the US Department of Energy Los Alamos, Argonne, and Brookhaven National Laboratories, and the Institute for Electronic and Digital Technologies (INSA) in Rennes, France, have discovered that in some 2D perovskites, sunlight effectively shrinks. the space between atoms, improving their ability to carry current.
“We find that when you light the material, you squeeze it like a sponge and bring the layers together to improve load transport in that direction,” Mohite said. The researchers found that placing a layer of organic cations between the iodide at the top and the lead at the bottom improved the interactions between the layers.
“This work has important implications for the study of excited states and quasiparticles in which a positive charge is on one layer and the negative charge is on the other and they can talk to each other,” Mohite said. “These are called excitons, which can have unique properties.
“This effect gave us the opportunity to understand and adapt these fundamental light-matter interactions without creating complex heterostructures like stacked 2D transition metal dichalcogenides,” he said.
The experiments were confirmed by computer models by colleagues in France. “This study offered a unique opportunity to combine state-of-the-art ab initio simulation techniques, material studies using large-scale national synchrotron radiation facilities and in situ characterizations of operating solar cells,” said Jacky Even, professor of physics at INSA. “The article describes for the first time how a percolation phenomenon suddenly releases the flow of charge current in a perovskite material.”
Both results showed that after 10 minutes under a solar simulator at solar intensity, the 2D perovskites contracted 0.4% along their length and about 1% up and down. They demonstrated that the effect can be observed in 1 minute under an intensity of five suns.
“It doesn’t sound like much, but this 1% contraction in lattice spacing induces a great improvement in electron flow,” said Wenbin Li, graduate student and co-lead author of Rice. “Our research shows a threefold increase in the electronic conduction of the material. “
At the same time, the nature of the mesh made the material less prone to degradation, even when heated to 80 degrees Celsius (176 degrees Fahrenheit). The researchers also found that the array quickly relaxed back to its normal configuration after the light was turned off.
“One of the main attractions of 2D perovskites was that they typically contain organic atoms which act as moisture barriers, are thermally stable, and solve problems with ion migration,” said Siraj Sidhik, graduate student and co-lead author. “3D perovskites are prone to heat and light, which is why researchers started placing 2D layers on loose perovskites to see if they could get the most out of both.
“We thought, let’s just go to 2D and make it efficient,” he said.
To observe the contraction of the material in action, the team used two user facilities from the US Department of Energy (DOE) Office of Science: the National Synchrotron Light Source II at DOE’s Brookhaven National Laboratory and the Advanced Photon Source. (APS) at the Argonne National of the DOE. Laboratory.
Argonne physicist Joe Strzalka, co-author of the article, used ultra-bright X-rays from APS to capture tiny structural changes in the material in real time. The sensitive instruments of the 8-ID-E beamline of the APS allow “operando” studies, that is to say those carried out while the device undergoes controlled changes of temperature or environment in environments. normal operating conditions. In this case, Strzalka and his colleagues exposed the photoactive material of 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 also kept the room in the dark and raised the temperature, observing the opposite effect: an expansion of the material. This showed that it was the light itself, and not the heat it generated, that was causing the transformation.
“For changes like this, it’s important to do operando studies,” Strzalka said. “The same way your mechanic wants to run your engine to see what’s going on inside, we basically want to take a video of that transformation instead of just one snapshot. Facilities such as APS allow us to do this.
Strzalka noted that the APS is in the midst of a major upgrade that will increase the brightness of its x-rays by up to 500 times. When completed, he said, the brighter beams and faster, more accurate detectors will improve the ability of scientists to detect these changes even more sensitively.
This could help the Rice team fine-tune the materials for even better performance. “We are on track to achieve over 20% efficiency in designing cations and interfaces,” said Sidhik. “That would change everything in the perovskite business, as people would then start using 2D perovskites for 2D perovskite / silicon and 2D / 3D perovskite tandems, which could lead to yields approaching 30%. This would make it attractive for marketing.
Reference: “Light-activated intercalary contraction in two-dimensional perovskites for high efficiency solar cells” by Wenbin Li, Siraj Sidhik, Boubacar Traore, Reza Asadpour, Jin Hou, Hao Zhang, Austin Fehr, Joseph Essman, Yafei Wang, Justin M Hoffman, Ioannis Spanopoulos, Jared J. Crochet, Esther Tsai, Joseph Strzalka, Claudine Katan, Muhammad A. Alam, Mercouri G. Kanatzidis, Jacky Even, Jean-Christophe Blancon and Aditya D. Mohite, November 22, 2021, Nature Nanotechnology.
DOI: 10.1038 / s41565-021-01010-2
The co-authors of the article are Jin Hou, Hao Zhang and Austin Fehr, graduate students of Rice, Joseph Essman, exchange student Yafei Wang and co-corresponding author Jean-Christophe Blancon, senior scientist at the Mohite laboratory; Boubacar Traoré, Claudine Katan at INSA; Reza Asadpour and Muhammad Alam of Purdue; Justin Hoffman, Ioannis Spanopoulos and Mercouri Kanatzidis of Northwestern; Jared Crochet from Los Alamos and Esther Tsai from Brookhaven.
The Army Research Office, the Institut universitaire de France, the National Science Foundation (20-587, 1724728), the Office of Naval Research (N00014-20-1-2725) and the DOE Office of Science (AC02-06CH11357) supported the research.