A material unfamiliar to the masses may provide a huge leap in solar energy technology over the next few years.
It’s called perovskite, a naturally occurring crystal structure that, when grown in the lab, has the capacity to convert solar energy to electricity by absorbing light and separating electrical charges in the material. Unlike its more mature cousin, the silicon semiconductor in solar cell applications, perovskite is more flexible and cheaper to manufacture. It just hasn’t met the test of longevity – yet.
Silicon solar cells, made from silicon wafers, have a useful life of 20 years, meaning they degrade by 5 percent a year. Perovskites are spin-coated on a surface, analogous to painting it on the surface – but they degrade more quickly. For now.
That’s according to Principal Scientist Alex Siemiarczuk, Ph.D. of HORIBA Scientific’s Fluorescence Division. He helps researchers understand HORIBA’s technology in spectrophotometry and in this case, how it applies to making a more efficient perovskite solar cell.
The efficiencies of perovskite solar cells have gone from single digits to a certified 22.1 percent in a few years’ time, according to a 2017 story published in Science Magazine. That is quickly approaching the efficiencies of traditional crystalline silicon solar cells.
It’s a “promising way to offset carbon emissions and meet increasing demand in energy consumption,” according to the story.
Perovskite can be applied in a liquid form. It can be painted onto objects, like buildings, clothing and even windows.
Researchers have been experimenting with hybrid perovskites, mimicking the physical chemical structure of perovskites, but introducing new elements into its formation to increase efficiencies and resilience.
“Perovskites are essentially crystals,” Siemiarczuk said. “The original perovskite mineral was composed of two metals and three atoms of oxygen,” Siemiarczuk said. “Depending on the application, you will have different groups used, for example, methylammonium, lead and three halide atoms. And that's what is commonly used in photovoltaics.”
In energy applications of solar cells, the perovskite layer is the light harvesting layer. The light is absorbed by the light harvesting layer, and there is charge separation, transport, and charge collection. As a result, some voltage is generated between the electrodes of the solar cell.
To better understand those critical processes and to improve the efficiency and stability of perovskite solar cell, some researchers employ the HORIBA’s hybrid fluorometers QuantaMaster™, Fluorolog and FluoroMax®, combined with HORIBA-IBH lifetime components for both fluorescence steady state and lifetime measurements, according to Ben Yang, Ph.D., an Applications Scientist for the fluorescence division of HORIBA Scientific. These are used by basic research labs trying to discover the photo-physical properties of hybrid perovskites and applied research labs, where scientists are trying to monetize the perovskite technology.
“The efficiency of this largely depends on how far those charge carriers can diffuse, and how long the electrons and holes can stay separated before recombination. One technology used often is the fluorescence lifetime, which can be used to measure carrier separation lifetime. We offer both hybrid fluorometers, and dedicated lifetime instruments like DeltaFlex and DeltaPro, manufactured in our Scottish facility, HORIBA-IBH. We come with our equipment so we can actually assess the efficiency of this light harvesting process. Photoluminescence allows you to assess the function and efficiency of your device,” Yang said.
Jinsong Huang, Ph.D., and Professor in the Department of Applied Physical Sciences University of North Carolina is working on providing solutions to industry to commercialize perovskite solar cells. His team provides scientific support to overcome the major technology barriers so that perovskite solar cells can be manufactured at a competitive price in large scale, by addressing issues related to stability, efficiency, and large scale and fast fabrication. He also conducts research to understand the unique properties of hybrid perovskites to find out why they are so good at photovoltaics.
He is also investigating other uses of perovskites.
“In addition to solar cells, we do research to find applications that perovskites not only fit, but also are much better than existing materials, such as sensitive ultrafast perovskite photodetectors, and perovskite X-ray detectors which are more than 1,000 times more sensitive than commercial X-ray detectors in medical imaging devices,” he said.
Huang employs HORIBA Scientific’s DeltaFlex turnkey TCSPC florescence lifetime spectrofluorometer. He uses it to measure the recombination rate in detecting their efficiencies.
“It’s a parameter we need to know,” he said.
Due to their nonlinear optical properties, perovskites are also used in laser technology to enhance frequency doubling of the coherent light source and generate laser output at shorter wavelengths.
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