Study Reveals New Insights into How Hybrid Perovskite Solar Cells Work

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The researchers also found that terahertz light fields are much stronger when perovskite is hit with high-energy light waves.

“We found that radiated terahertz light is orders of magnitudes more intense when you excite the electrons with violet light versus low-energy infrared light,” Lindenberg said. “That was an unexpected result.”

This discovery could provide new insights on high-energy “hot” electrons, Guzelturk said.

“Violet light imparts electrons with excess kinetic energy, creating hot electrons that move much faster than other electrons,” he said. “However, these hot electrons lose their excess energy very rapidly.”

Harnessing the energy from hot electrons could lead to a new generation of high-efficiency solar cells, added Lindenberg.

“One of the grand challenges is finding a way to capture the excess energy from a hot electron before it relaxes,” he said. “The idea is that if you could extract the current associated with hot electrons before the energy dissipates, you could increase the efficiency of the solar cell. People have argued that it’s possible to create hot electrons in perovskites that live much longer than they do in silicon. That’s part of the excitement around perovskites.”

The study revealed that in hybrid perovskites, hot electrons separate from holes faster and more efficiently than electrons excited by infrared light.

“For the first time we can measure how fast this separation occurs,” Lindenberg said. “This will provide important new information on how to design solar cells that use hot electrons.” 

Toxicity and Stability

The ability to measure terahertz emissions could also lead to new research on non-toxic alternatives to conventional lead-based perovskites, said Guzelturk.

“Most of the alternative materials being considered are not as efficient at generating electricity as lead,” he said. “Our findings might allow us to understand why lead composition works so well while other materials don’t, and to investigate the degradation of these devices by looking directly at the atomic structure and how it changes.”

Other co-authors of the study are staff scientist Christopher Tassone and postdoctoral scholar Karsten Bruening with SLAC’s SSRL Materials Science Division; Hemamala Karunadsa, assistant professor of chemistry, and graduate students Rebecca Belisle, Rohit Prasanna and Matthew Smith at Stanford; and Venkatraman Gopalan, professor of materials science and engineering, and graduate student Yakun Yuan at Pennsylvania State University.

The work was funded by SLAC, the National Science Foundation and the DOE Office of Science. SIMES is jointly operated by Stanford and SLAC.

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