Cheaper, Super-Efficient Solar Power

Pictured: Electrons are shown in red, holes in blue, and the arrows indicate an applied magnetic field. (Photo : University of Utah)

Revealing the Secret to Cheaper, Super-Efficient Solar Power

Scientists are helping to reveal the secret to cheaper, super-efficient solar power by studying a family of crystalline materials called hybrid perovskites.

It has taken decades of research to develop top-performing materials that can generate electricity from sunlight. And yet hybrid perovskite solar cells, a method that has only been explored for the last five years, are just as efficient in converting to solar power. Until now, it was unclear what occurred in the hybrid perovskite solar cells on a molecular level to lead to such amazing power performance. But researchers at the University of Utah are finally helping to answer some of these puzzling questions.

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The findings were published in the journal Nature Physics. 

Perhaps the most useful part of the recent study is the discovery of a way to quickly test the performance of different prototypes of hybrid perovskite materials using magnetic fields.

By applying a magnetic field, the researchers can determine how it influences the behavior of electrons and "holes" in semiconductor compounds. Contrary to popular belief, the Utah team found that there were significant magnetic field effects; and the magnetic properties of two heavy atoms, lead and iodine, were observed to minimize these effects in hybrid perovskite solar cells.

"Our group has unique expertise in magnetic field effects," senior author Z. Valy Vardeny, a physics professor at the University of Utah, said in a statement. "We wanted to see if magnetic field effects would tell us why the efficiency is so high."

The researchers identified a mechanism, dubbed delta-g, that could help explain how a magnetic field influences the spin configuration of electron-hole pairs. The spin configuration changes the rate at which electron-hole pairs split apart or recombine, which thus has an effect on the electrical conductivity and photoluminescence of the perovskite. Using a technique called field-induced circular polarized emission, they were able to measure delta-g directly. They also used a spectroscopy technique to observe the lifetimes of electron-hole pairs created by light absorption in the hybrid perovskite solar cells - which can be as fleeting as mere trillionths of a second.

Together these results all proved to line up with the idea of delta-g.

The findings help to answer the longstanding question as to whether hybrid perovskite devices behave more like silicon solar cells or like so-called excitonic solar cells made of organic polymers.

"This material is not excitonic. If it were, we would not see this effect. It is not like organic photovoltaic materials," said Vardeny.

Currently, the perovskite photovoltaic devices can produce solar power with an efficiency of nearly 20 percent. And while that's not quite as impressive as the 26 percent the best silicon cells are capable of, researchers hope soon hybrid perovskites will bridge that gap.

Harnessing solar energy through photovoltaic cells has become easier with the development of hybrid perovskite, not to mention cheaper.

"This is important since the gasoline price at the pumps would not stay that low forever," Vardeny concluded.

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