Researchers Develop Recyclable Solar Cells From Trees

Since they already absorb energy from the sun and transform it, trees seem like a natural fit for solar-cell technology, which does ostensibly the same thing. Now, researchers from the Georgia Institute of Technology have come up with a way to use a natural material in trees to develop solar cells that pave the way for recyclable, sustainable, and renewable solar-cell technology.

To be clear, the part of the cell developed by Georgia Tech College of Engineering Professor Bernard Kippelen and his team that absorbs sunlight and transforms it into electricity is a chemical -- specifically, one derived from petroleum chemistry.

However, they have created the substrate of the cell, or its thickest part, with cellulose nano-crystal (CNC), which is derived from trees. Typically, this part of solar cells -- a thousand times thicker than the reactive material that does the energy conversion -- is fabricated on glass or plastic, neither of which is easily recyclable or eco-friendly.

CNC, on the other hand, is a natural material, and thus both of these things, Kippelen told Design News. "By replacing the substrate with natural materials, the solar cells can easily be recycled and separated into their components by immersing them in water," he said. "That ease of recycling can make this technology greener than conventional photovoltaic technologies." The yield of producing cellulose nanocrystals from dry wood is about 20 percent, he told us.

Kippelen learned of the possibility to create cell substrates with cellulose nanocrystals in early 2011 at an event organized by the Institute of Paper Science and Technology:

Learning that transparent substrates could be fabricated from biomass like wood was very intriguing since our main research deals with flexible and printed organic electronic devices. We study devices like light-emitting diodes and solar cells. Both type of devices are generally deposited on top of a transparent substrate.

Before fully embarking on his current research, he studied ardently about nanocellulose research, and met with fellow researchers from Purdue University, R.J. Moon and Jeff Youngblood, with whom he eventually collaborated on the technology.

Researchers are now working to increase the power conversion efficiency of the cells, which is currently 2.7 percent -- uncommonly high for cells with substrates derived from renewable raw materials, they said.

Kippelen and his team aim to optimize the optical properties of the cell's electrode to improve the power-conversion efficiency of the cells to more than 10 percent, a level similar to cells fabricated with glass or plastic based substrates. They also have filed a provision technology patent for the technology with the US Patent Office.

Since the technology is in its nascent stages, it remains to be seen if and when the cells will make it into the commercial market. "At this time, we have validated the concept, and suggested a new path forward for greener renewable energy, but much research remains to be done before they can be manufactured and mass produced," Kippelen said.

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