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Researchers gain important insights into the efficiency of solar materials



  Researchers gain important insights into the efficiency of solar materials
The addition of selenium to cadmium telluride solar cells improves their performance. New research explains why. Credit: First Solar

The rows of blue solar panels that cover landscapes and roofs are usually made of crystalline silicon, the workhorse semiconductor that can be found in virtually every electronic device.

Over the past decade, Colorado State University researchers have pioneered studies to improve the performance and cost of solar energy by producing and testing new materials that go beyond the capabilities of silicon. They focused on a material that is promising to replace silicon, cadmium telluride.

Collaborating with partners at Loughborough University, UK, researchers at CSU's Next Generation Photovoltaics Center supported by the National Science Foundation announced a major breakthrough in how to further improve the performance of cadmium telluride thin film solar cells by adding another material, selenium becomes. Their findings were published earlier this month in the journal Nature Energy and are the subject of an article "News and Views".

"Our work directly addresses the fundamental understanding of what happens when we alloy selenium to cadmium telluride," said Kurt Barth, director of the Next Generation Photovoltaics Center and associate research professor at the Department of Mechanical Engineering.

So far it was not clear why the addition of selenium recorded record levels The efficiency of cadmium telluride solar cells ̵

1; the ratio of energy output to light output – is just over 22 percent. Together with CSU employees W.S. Sampath and Amit Munshi, Barth and an international team have solved this puzzle. Their experiments showed that selenium overcomes the effects of atomic scale defects in cadmium telluride crystals, opening a new path for the diffusion of cheaper solar power.

The cadmium telluride thin films produced by the CSU team in the lab are 100 times less material than conventional silicon solar modules. They are thus easier to manufacture and absorb sunlight at almost the ideal wavelength. Electricity generation from cadmium telluride photovoltaic cells is the most cost-effective in the solar industry and undercuts fossil fuels in many regions of the world.

According to the paper, electrons are generated when sunlight hits the selenium-treated solar panel. They are less likely to be trapped and lost due to the material defects that are at the boundaries between the crystal grains as they grow. This increases the amount of energy taken from each solar cell. Working with materials produced at the CSU using advanced deposition techniques, the team discovered this unexpected behavior by determining the light emission from selenium-containing panels.

Because selenium is not evenly distributed across the panels, they compared the luminescence of areas where light is emitted. There was little to no selenium and areas where the selenium was very concentrated.

"Good solar cell material that has no defects emits light very efficiently and therefore shines very brightly," said Tom Fiducia's lead author and Ph.D. Student at the University of Loughborough in collaboration with Professor Michael Walls. "It's noticeable when you see the data that selenium-rich regions are much brighter than pure cadmium telluride, and the effect is remarkably strong."


Researchers solve a scientific puzzle that could improve the efficiency of solar modules


Further information:
Thomas A. M. Fiducia et al., Understanding the Role of Selenium in the Passive Passivation of Highly Efficient Selenium-Selected Cadmium Celluride Solar Cells, Nature Energy (2019). DOI: 10.1038 / s41560-019-0389-z

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Colorado State University




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Researchers gain important insights into the efficiency of solar materials (2019, 23 May)
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