Nanotechnology Now

Our NanoNews Digest Sponsors

Heifer International

Wikipedia Affiliate Button

Home > Press > Atomic movies may help explain why perovskite solar cells are more efficient: SLAC's ultrafast 'electron camera' captures surprising atomic motions in these next-generation materials

Illustration of the ultrafast electron diffraction (UED) experiment used to capture the rapid atomic response to light in perovskites. An electron beam (blue) is deflected as it passes through the perovskite sample, generating an intensity or diffraction pattern on a detector that allows the reconstruction of the sample’s atomic structure. By measuring how the pattern changes over time after the sample was hit by a laser pulse (red), researchers can create an ultrafast movie of the atomic response. (Greg Stewart/SLAC National Accelerator Laboratory)
Illustration of the ultrafast electron diffraction (UED) experiment used to capture the rapid atomic response to light in perovskites. An electron beam (blue) is deflected as it passes through the perovskite sample, generating an intensity or diffraction pattern on a detector that allows the reconstruction of the sample’s atomic structure. By measuring how the pattern changes over time after the sample was hit by a laser pulse (red), researchers can create an ultrafast movie of the atomic response. (Greg Stewart/SLAC National Accelerator Laboratory)

Abstract:
In recent years, perovskites have taken the solar cell industry by storm. They are cheap, easy to produce and very flexible in their applications. Their efficiency at converting light into electricity has grown faster than that of any other material - from under four percent in 2009 to over 20 percent in 2017 - and some experts believe that perovskites could eventually outperform the most common solar cell material, silicon. But despite their popularity, researchers don't know why perovskites are so efficient.

Atomic movies may help explain why perovskite solar cells are more efficient: SLAC's ultrafast 'electron camera' captures surprising atomic motions in these next-generation materials

Menlo Park, CA | Posted on July 28th, 2017

Now experiments with a powerful "electron camera" at the Department of Energy's SLAC National Accelerator Laboratory have discovered that light whirls atoms around in perovskites, potentially explaining the high efficiency of these next-generation solar cell materials and providing clues for making better ones.

"We've taken a step toward solving the mystery," said Aaron Lindenberg from the Stanford Institute for Materials and Energy Sciences (SIMES) and the Stanford PULSE Institute for ultrafast science, which are jointly operated by Stanford University and SLAC. "We recorded movies that show that certain atoms in a perovskite respond to light within trillionths of a second in a very unusual manner. This may facilitate the transport of electric charges through the material and boost its efficiency."

The study was published today in Science Advances.

Light Sets Atomic Structure in Motion

When light shines on a solar cell material, its energy displaces some of the material's negatively charged electrons. This leaves behind "electron holes" with a positive charge where the electrons were originally located. Electrons and holes migrate to opposite sides of the material, creating a voltage that can be used to power electrical devices.

A solar cell's efficiency depends on how freely electrons and holes can move in the material. Their mobility, in turn, depends on the material's atomic structure. In silicon solar cells, for example, silicon atoms line up in a very orderly fashion inside crystals, and even the smallest structural defects reduce the material's ability to efficiently harvest light.

As a result, silicon crystals must be grown in costly, multistep procedures under extremely clean conditions. In contrast, "Perovskites are readily produced by mixing chemicals into a solvent, which evaporates to leave a very thin film of perovskite material," said Xiaoxi Wu, the study's lead author from SIMES at SLAC. "Simpler processing means lower costs. Unlike silicon solar cells, perovskite thin films are also lightweight and flexible and can be easily applied to virtually any surface."

But what exactly is it about perovskites that allows some of them to harvest light very efficiently? Scientists think that one of the keys is how their atoms move in response to light.

To find out more, Wu and her colleagues studied these motions in a prototype material made of iodine, lead and an organic molecule called methylammonium. The iodine atoms are arranged in octohedra - eight-sided structures that look like two pyramids joined at their bases. The lead atoms sit inside the octohedra and the methylammonium molecules sit between octohedra (see diagram below). This architecture is common to many of the perovskites investigated for solar cell applications.

"Previous studies have mostly explored the role of the methylammonium ions and their motions in transporting electric charge through the material," Wu said. "However, we've discovered that light causes large deformations in the network of lead and iodine atoms that could be crucial for the efficiency of perovskites."

Unusual Distortions May Enhance Efficiency

At SLAC's Accelerator Structure Test Area (ASTA), the researchers first hit a perovskite film, less than two millionths of an inch thick, with a 40-femtosecond laser pulse. One femtosecond is a millionth of a billionth of a second. To determine the atomic response, they sent a 300-femtosecond pulse of highly energetic electrons through the material and observed how the electrons were deflected in the film. This technique, called ultrafast electron diffraction (UED), allowed them to reconstruct the atomic structure.

"By repeating the experiment with different time delays between the two pulses, we obtained a stop-motion movie of the lead and iodine atoms' motions after the light hit," said co-author Xijie Wang, SLAC's lead scientist for UED. "The method is similar to taking a series of ultrafast X-ray snapshots, but electrons give us much stronger signals for thin samples and are less destructive."

The team expected that the light pulse would affect atoms evenly in all directions, causing them to jiggle around their original positions.

"But that's not what happened," Lindenberg said. "Within 10 trillionths of a second after the laser pulse, the iodine atoms rotated around each lead atom as if they were moving on the surface of a sphere with the lead atom at the center, switching each octahedron from a regular shape to a distorted one."

The surprising deformations were long-lived and unexpectedly large, similar in size to those observed in melting crystals.

"This motion could alter the way charges move," Wu said. "This response to light could enhance efficiency, for instance by allowing electric charges to migrate through defects and protecting them from being trapped in the material."

"The results from the Lindenberg group provide fascinating first-time insights into the properties of hybrid perovskites using ultrafast electron diffraction as a unique tool," according to Felix Deschler, an expert in the field of light-induced physics of novel materials and a researcher at Cambridge University's Cavendish Lab.

"Knowledge about the detailed atomic motion after photoexcitation yields new information about their performance and can provide new guidelines for material development."

###

This work was funded by the DOE Office of Science through SIMES. Other contributors came from the University of Pennsylvania, Columbia University and the Weizmann Institute of Science in Israel.

####

About SLAC National Accelerator Laboratory
SLAC is a multi-program laboratory exploring frontier questions in photon science, astrophysics, particle physics and accelerator research. Located in Menlo Park, California, SLAC is operated by Stanford University for the U.S. Department of Energy Office of Science. To learn more, please visit http://www.slac.stanford.edu .

SLAC National Accelerator Laboratory is supported by the Office of Science of the U.S. Department of Energy. The Office of Science is the single largest supporter of basic research in the physical sciences in the United States, and is working to address some of the most pressing challenges of our time. For more information, please visit science.energy.gov.

For more information, please click here

Contacts:
Andrew Gordon

650-926-2282

Copyright © SLAC National Accelerator Laboratory

If you have a comment, please Contact us.

Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.

Bookmark:
Delicious Digg Newsvine Google Yahoo Reddit Magnoliacom Furl Facebook

Related News Press

Laboratories

Supersonic waves may help electronics beat the heat May 18th, 2018

Hematene joins parade of new 2D materials: Rice University-led team extracts 3-atom-thick sheets from common iron oxide May 8th, 2018

Scientists Pinpoint Energy Flowing Through Vibrations in Superconducting Crystals: Interactions between electrons and the atomic structure of high-temperature superconductors impacted by elusive and powerful vibrations May 4th, 2018

News and information

Supersonic waves may help electronics beat the heat May 18th, 2018

New blood test rapidly detects signs of pancreatic cancer May 17th, 2018

Disability Can Be a Superpower in Space Disabled astronauts offer unique solutions to emergencies in space May 17th, 2018

Deeper understanding of quantum chaos may be the key to quantum computers May 16th, 2018

Imaging

Elastic microspheres expand understanding of embryonic development and cancer cells May 15th, 2018

Nanoscale measurements 100x more precise, thanks to improved two-photon technique May 8th, 2018

Perovskites

High efficiency solar power conversion allowed by a novel composite material: A composite thin film developed at INRS improves significantly solar cells' power conversion efficiency April 10th, 2018

Double perovskites in environmentally friendly solar cells: Long electron-hole diffusion length in high-quality lead-free double perovskite films April 6th, 2018

Inorganic-organic halide perovskites for new photovoltaic technology November 6th, 2017

Missing atoms in a forgotten crystal bring luminescence October 10th, 2017

Govt.-Legislation/Regulation/Funding/Policy

Supersonic waves may help electronics beat the heat May 18th, 2018

New blood test rapidly detects signs of pancreatic cancer May 17th, 2018

Deeper understanding of quantum chaos may be the key to quantum computers May 16th, 2018

Team achieves two-electron chemical reactions using light energy, gold May 15th, 2018

Possible Futures

Supersonic waves may help electronics beat the heat May 18th, 2018

New blood test rapidly detects signs of pancreatic cancer May 17th, 2018

Disability Can Be a Superpower in Space Disabled astronauts offer unique solutions to emergencies in space May 17th, 2018

Deeper understanding of quantum chaos may be the key to quantum computers May 16th, 2018

Discoveries

Supersonic waves may help electronics beat the heat May 18th, 2018

New blood test rapidly detects signs of pancreatic cancer May 17th, 2018

Deeper understanding of quantum chaos may be the key to quantum computers May 16th, 2018

Making carbon nanotubes as usable as common plastics: Researchers discover that cresols disperse carbon nanotubes at unprecedentedly high concentrations May 15th, 2018

Announcements

Supersonic waves may help electronics beat the heat May 18th, 2018

New blood test rapidly detects signs of pancreatic cancer May 17th, 2018

Disability Can Be a Superpower in Space Disabled astronauts offer unique solutions to emergencies in space May 17th, 2018

Deeper understanding of quantum chaos may be the key to quantum computers May 16th, 2018

Tools

A micro-thermometer to record tiny temperature changes May 15th, 2018

Elastic microspheres expand understanding of embryonic development and cancer cells May 15th, 2018

Nanoscale measurements 100x more precise, thanks to improved two-photon technique May 8th, 2018

Leti and Cellmic Join Forces to Speed Market Adoption of Lens-Free Imaging and Sensing Techniques May 3rd, 2018

Energy

Team achieves two-electron chemical reactions using light energy, gold May 15th, 2018

Hematene joins parade of new 2D materials: Rice University-led team extracts 3-atom-thick sheets from common iron oxide May 8th, 2018

A designer's toolkit for constructing complex nanoparticles May 5th, 2018

Scientists Pinpoint Energy Flowing Through Vibrations in Superconducting Crystals: Interactions between electrons and the atomic structure of high-temperature superconductors impacted by elusive and powerful vibrations May 4th, 2018

Research partnerships

Deeper understanding of quantum chaos may be the key to quantum computers May 16th, 2018

Nanoscale measurements 100x more precise, thanks to improved two-photon technique May 8th, 2018

Hematene joins parade of new 2D materials: Rice University-led team extracts 3-atom-thick sheets from common iron oxide May 8th, 2018

Harvesting clean hydrogen fuel through artificial photosynthesis May 3rd, 2018

Solar/Photovoltaic

Team achieves two-electron chemical reactions using light energy, gold May 15th, 2018

Hematene joins parade of new 2D materials: Rice University-led team extracts 3-atom-thick sheets from common iron oxide May 8th, 2018

Harvesting clean hydrogen fuel through artificial photosynthesis May 3rd, 2018

Research gives new ray of hope for solar fuel April 27th, 2018

NanoNews-Digest
The latest news from around the world, FREE



  Premium Products
NanoNews-Custom
Only the news you want to read!
 Learn More
NanoStrategies
Full-service, expert consulting
 Learn More











ASP
Nanotechnology Now Featured Books




NNN

The Hunger Project