When scientists applied pressure to perovskite solar cells, they found they could tailor the wavelength of light the materials absorbed.

“Our results suggest that we can increase the voltages of perovskite solar cells by applying external pressure,” says Hemamala Karunadasa, an assistant professor of chemistry at Stanford University. “We also observed a dramatic increase in the electronic conductivity of these promising materials at high pressures.”

Karunadasa and colleague Wendy Mao recently published their findings in the journal ACS Central Science.

Perovskites come in several crystalline structures, including hybrid perovskites made of lead, iodine, or bromine, and organic compounds. The inexpensive materials have potential applications in advancing LEDs and lasers, but one of the hottest areas of research involves solar cells.

Recent studies have shown that hybrid perovskites efficiently absorb sunlight and convert it to electricity. Several labs have achieved efficiencies above 20 percent, rivaling commercially available silicon solar cells.

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Karunadasa and Mao wanted to find out how pressure affects the way hybrid perovskites respond to light. They loaded perovskite samples in a diamond-anvil cell, a high-pressure device consisting of two opposing diamonds. Each tiny sample was placed between the diamonds and then squeezed at very high pressures.

The results were visible. One sample, which is normally orange, turned lighter in color under compression, an indication that the perovskite was absorbing higher-energy light waves. But as the pressure increased, the sample darkened, indicating that lower-energy light was also being absorbed.

“Our findings suggest that compression can allow us to tailor the wavelength of absorbed light,” says Mao, an associate professor of geological sciences. “This compression may be attained through either mechanical or chemical means.”

Several research groups have been developing low-cost tandem solar cells made of perovskite stacked on top of silicon. But obtaining the high voltages required for high-efficiency tandem cells has proven difficult. The results of the new study suggest pressure can increase the voltages of perovskite solar cells and should be investigated further.

“By tracking the positions of atoms upon compression using X-ray diffraction, we can explain exactly how the materials’ structure responds to pressure,” Karunadasa says. “Overall, this work shows that pressure is a tuning knob for improving the properties of perovskite absorbers in a predictable way.”

Researchers from the SLAC National Accelerator Laboratory and Lawrence Berkeley National Laboratory collaborated on the work, which was funded by the National Science Foundation, the US Department of Energy, the Stanford Global Climate and Energy Project, and the Stanford Interdisciplinary Graduate Fellowship program.

Source: Stanford University

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