Examination of Single Perovskite Crystals Reveals Much Untapped Potential for Solar and LEDs

Engineers at the University of Toronto have for the first time demonstrated
some of the optoelectronic properties of pure perovskite crystals. This
emerging family of solar-absorbing materials and understanding their
optoelectronic properties could lead to more efficient and cheaper solar panels
and LEDs. Through their examination of the properties of single perovskite
materials, the researchers revealed that perovskites still have much untapped
potential for use in solar panels and LEDs.

The perovskites, are particularly good at absorbing visible light, but they
had never before been thoroughly studied as perfect single crystals. The
researchers employed a new technique to grow pure perovskite crystals and then
studied electrons move through the material as light is converted to

Professor Ted Sargent of the University of Toronto’s Edward S. Rogers Sr.
Department of Electrical & Computer Engineering and Professor Osman Bakr of
the King Abdullah University of Science and Technology (KAUST) used a
combination of laser-based techniques to measure certain properties of the
perovskite crystals. They tracked down the rapid motion of electrons in the
material. From this they were able to determine the diffusion length-how far
electrons can travel without imperfections in the material trapping them-as
well as mobility—how fast the electrons can move through the material.
This week, they published their work in the journal Science.

“Our work identifies the bar for the ultimate solar
energy-harvesting potential of perovskites,”
said Riccardo Comin, a
post-doctoral fellow with the Sargent Group. “With these materials
it’s been a race to try to get record efficiencies, and our results
indicate that progress is slated to continue without slowing

Certified efficiencies of perovskites have reached new heights of just over
20 percent in recent years. Such efficiency starts to approach the performance
of the state-of-the-art commercial-grade silicon-based solar panels mounted in
deserts in spain and on roofs in California.

“In their efficiency, perovskites are closely approaching
conventional materials that have already been commercialized,”
Valerio Adinolfi, a PhD candidate in the Sargent Group and co-first author of
the paper. “They have the potential to offer further progress on
reducing the cost of solar electricity in light of their convenient
manufacturability from a liquid chemical precursor.

In solar panels, light hits the surface of the perovskite material and gets
absorbed, thereby exciting electrons. These electrons easily traverse the
crystal structure to electrical contacts on the underside, creating electric
current. In LEDs the process happens in reverse. The slab is first powered with
electricity, which injects electrons and then releases energy as light.

The Sargent Group is conducting parallel work that aims to improve the
performance of solar-absorbing particles called colloidal quantum dots.
“Perovskites are great visible-light harvesters, and quantum dots are
great for infrared,” said Professor Sargent. “The materials are
highly complementary in solar energy harvesting in view of the sun’s
broad visible and infrared power spectrum.”

“In future, we will explore the opportunities for stacking
together complementary absorbent materials,”
said Dr. Comin.
“There are very promising prospects for combining perovskite work and
quantum dot work for further boosting the efficiency.”

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