Fabricating new plant-based solar cells on cellulose nanocrystal substrates means that they're recyclable in water.
The researchers report that the organic solar cells reach a power conversion efficiency of 2.7 percent, an unprecedented figure for cells on substrates derived from renewable raw materials.
The cellulose nanocrystal (CNC) substrates on which the solar cells are fabricated are optically transparent, which lets light pass through them before being absorbed by a very thin layer of an organic semiconductor.
During the recycling process, the solar cells are simply immersed in water at room temperature. Within minutes, the CNC substrate dissolves and the solar cell can be separated easily into its major components.
Professor Bernard Kippelen of Georgia Institute of Technology's College of Engineering led the study and says his team's project opens the door for a truly recyclable, sustainable, and renewable solar cell technology.
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"The development and performance of organic substrates in solar technology continues to improve, providing engineers with a good indication of future applications," says Kippelen, who is also the director of Georgia Tech's Center for Organic Photonics and Electronics (COPE).
"But organic solar cells must be recyclable. Otherwise we are simply solving one problem, less dependence on fossil fuels, while creating another, a technology that produces energy from renewable sources but is not disposable at the end of its lifecycle."
To date, organic solar cells have been typically fabricated on glass or plastic. Neither is easily recyclable, and petroleum-based substrates are not very eco-friendly. For instance, if cells fabricated on glass were to break during manufacturing or installation, the useless materials would be difficult to dispose of.
"Paper substrates are better for the environment, but have shown limited performance because of high surface roughness or porosity. However, cellulose nanomaterials made from wood are green, renewable, and sustainable. The substrates have a low surface roughness of only about two nanometers.
"Our next steps will be to work toward improving the power conversion efficiency over 10 percent, levels similar to solar cells fabricated on glass or petroleum-based substrates," says Kippelen. The group plans to achieve this by optimizing the optical properties of the solar cell's electrode.
There's also another positive impact of using natural products to create cellulose nanomaterials. The nation's forest product industry projects that tens of millions of tons of them could be produced once large-scale production begins, potentially in the next five years.
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Jeffrey Youngblood, an associate professor in Purdue University's School of Materials Engineering, collaborated with Kippelen on the research. Their findings appear in Scientific Reports.
A provisional patent on the technology has been filed with the US Patent Office.
This research was funded in part through the Center for Interface Science: Solar Electric Materials, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, by the Air Force Office of Scientific Research, by the Office of Naval Research, and the US Department of Agriculture-Forest Service.
The USDA-Forest Service provided funding for CNC substrate processing. The US Forest Service-Forest Products Laboratory (FPL) provided CNC materials.
By. Jason Maderer
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