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Researchers led by Joondong Kim, an electrical engineering professor at Incheon National University, Korea, recently demonstrated the first transparent solar cell. The team focused on the heterojunction, the thin films of materials responsible for absorbing light.

In today’s solar cells the semiconductor layers responsible for capturing light and translating it into an electrical current render them opaque. So the team decided to explore the use of two other materials to make those films.

The first material, titanium dioxide (TiO2), a well-known semiconductor already widely used to make solar cells. It has excellent electrical properties and is environmentally friendly and non-toxic. Titanium dioxide absorbs UV light while letting through most of the visible light. The second material was nickel oxide (NiO), another semiconductor with optical transparency. Nickel is one of the most abundant elements on Earth, and its oxide can easily be manufactured at low industrial temperatures, making it a good candidate for manufacturing eco-friendly solar cells.

The solar cell created by the team is transparent, which could enable future versions of it to be used in glass windows in houses and skyscrapers, as well as smaller applications such as watches and cell phones.Incheon National University

The team’s new solar cell is composed of a glass substrate and a metal oxide electrode, with thin layers of semiconductors (TiO2 first, then NiO) deposited on top. A final coating of silver nanowires serves as the cell’s other electrode.

Tests showed the cell had a power conversion efficiency of 2.1%, which the team says is good considering the cell uses only a small part of the light spectrum. The cell was also highly responsive and worked in low-light conditions. Furthermore, more than 57% of visible light gets transmitted through the cell layer, making it transparent. The researchers also showed that the cell can power a small motor.

“While this innovative solar cell is still very much in its infancy, our results strongly suggest that further improvements are possible for transparent photovoltaics by improving the cell’s optical and electrical properties,” suggests Kim.

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