New discoveries made about a promising material for solar cells, thanks to a new microscope

New discoveries made about a promising material for solar cells, thanks to a new microscope

Visualization of the microscope tip exposing the material to terahertz light. The colors of the material represent the light scattering data, and the red and blue lines represent the terahertz waves. Credit: US Department of Energy Ames National Laboratory.

A team of scientists at the Department of Energy’s Ames National Laboratory has developed a new characterization tool that allowed them to gain unique insight into a possible alternative material for solar cells. Led by Jigang Wang, Principal Scientist at Ames Lab, the team developed a microscope that uses terahertz waves to collect data on material samples. The team then used their microscope to explore methylammonium lead iodide (MAPbI3) perovskite, a material that could potentially replace silicon in solar cells.

Richard Kim, a scientist at Ames Lab, explained the two features that make the new scanning probe microscope unique. First, the microscope uses the terahertz range of electromagnetic frequencies to collect data about materials. This range is well below the visible light spectrum, falling between the infrared and microwave frequencies. Second, terahertz light shines through a sharp metal tip that enhances the microscope’s capabilities down to nanometer length scales.

“Normally, if you have a wave of light, you can’t see things smaller than the wavelength of the light you’re using. And for this terahertz light, the wavelength is about a millimeter, so it’s quite big,” Kim explained. “But here we use this sharp metal tip with an apex that tapers to a radius curvature of 20 nanometers, and this acts as our antenna to see things smaller than light. wavelength that we were using.”

Using this new microscope, the team investigated a perovskite material, MAPbI.3, which has recently become of interest to scientists as an alternative to silicon in solar cells. Perovskites are a special type of semiconductor that carry a electric charge when exposed to visible light. The main challenge to use MAPbI3 in Solar cells it is that it easily degrades when exposed to elements such as heat and humidity.

According to Wang and Kim, the team hoped that MAPbI3 behave like an insulator when exposed to terahertz light. Since the data collected on a sample is a reading of how light is scattered when the material is exposed to terahertz waves, they expected a constant low level of light scattering throughout the material. What they found, however, was that there was a lot of variation in light scattering along the grain boundary.

Kim explained that conductive materials, such as metals, would have a high level of light scattering, while less conductive materials, such as insulators, would not. The wide variation of light scattering detected along grain boundaries in MAPbI3 sheds light on the problem of material degradation.

Over the course of a week, the team continued to collect data on the material, and the data collected in that time showed the degradation process through changes in light scattering levels. This information may be useful for improving and manipulating the material in the future.

“We believe that the present study demonstrates a powerful microscopy tool to visualize, understand, and potentially mitigate grain boundary degradation, defect traps, and material degradation,” Wang said. “A better understanding of these issues can enable the development of highly efficient perovskite-based photovoltaic devices for many years.”

MAPbI samples3 They were provided by the University of Toledo. This research is discussed in more detail in the article “Terahertz Nanoimaging of Perovskite Solar Cell Materials,” written by Richard HJ Kim, Zhaoyu Liu, Chuankun Huang, Joong-Mok Park, Samuel J. Haeuser, Zhaoning Song, Yanfa Yan, Yongxin Yao , Liang Luo and Jigang Wang, and published in the ACS Photonics.

More information:
Richard HJ Kim et al, Terahertz Nanoimaging of Perovskite Solar Cell Materials, ACS Photonics (2022). DOI: 10.1021/acsphotonics.2c00861

Provided by
Ames Laboratory

Citation: New Discoveries Made About a Promising Material for Solar Cells, Thanks to a New Microscope (November 15, 2022) Accessed November 16, 2022 at cell-material-microscope. html

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