Researchers from Georgia Institute of Technology and Purdue University, USA, have developed efficient solar cells using natural substrates derived from plants such as trees, which making these solar cells can be quickly recycled in water at the end of their lifecycle.
The solar cells are fabricated on the cellulose nanocrystal (CNC) substrates which are optically transparent, enabling light to pass through them before being absorbed by a very thin layer of an organic semiconductor. Researchers have achieved 2.7% of cell efficiency. During the recycling process, the solar cells are simply immersed in water at room temperature. Within only minutes, the CNC substrate dissolves and the solar cell can be separated easily into its major components.
“The development and performance of organic substrates in solar technology continues to improve, providing engineers with a good indication of future applications,” said Bernard Kippelen, 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. Paper substrates are better for the environment, but have shown limited performance because of high surface roughness or porosity. However, CNC made from wood are green, renewable and sustainable. The substrates have a low surface roughness of only about 2 nanometers.
“Our next steps will be to work toward improving the power conversion efficiency over 10%, levels similar to solar cells fabricated on glass or petroleum-based substrates,” said Kippelen. The group plans to achieve this by optimizing the optical properties of the solar cell’s electrode.