Researchers at Georgia Institute of Technology and Purdue University have devised a solar cell that makes solar energy truly renewable.
|Recyclable solar cell made of cellulose and vials that contain the different |
parts of the cell after it was dissolved in water and the organic solvent.
Photo courtesy: Canek Fuentes-Hernandez
For all their renewable energy benefits, many current photovoltaic solar cells are made with glass, and plastic or petroleum-based materials that are both expensive to produce and difficult to recycle. Solar cells made with organic materials are comparatively cheaper to make, mechanically flexible and are more easily recycled. The team at Georgia Institute of Technology and Purdue University selected to focus on a familiar organic material: cellulose.
Cellulose is like the cinder block of the plant world. In tree leaves, cellulose gives the plant cell walls their structure. Under a microscope, you can also see how cellulose forms tiny needle-like crystals. In their study, the researchers used a transparent sheet of these cellulose nanocrystals (CNC's) as the base for a small solar cell. Light traveled through the transparent CNC substrate and was absorbed by a very thin organic semiconductor where the energy of the photons creates an electrical current.
A common measurement of how well a solar cell works is its power conversion efficiency. The power conversion efficiency of a solar cell measures how much of the incoming energy from the sun is converted into energy we can use as electricity.
Current commercial solar cells average about 15% efficiency. The researchers report their new cellulose substrate organic solar cell had 2.7% power conversion efficiency. While 2.7% is a ways away from 15%, the researchers believe that their cellulose-based solar cell could be competitive with commercial technologies if they can push the power conversion efficiency to only 5% and have their devices last 5 years.
This brings us to one of the most intriguing aspects of a cellulose-based organic solar cell. We have a huge amount of technological detritus. From old batteries to computers, TVs, radios, and cellphones, old electronics produce an enormous amount of toxic trash.
A cornerstone of the new research is the biodegradability of cellulose-based photovoltaics. The scientists report that their solar cell essentially dissolves in room temperature water. While they don't say how this might work in the case of rain, the researchers write that their cellulose substrate dissolves and each component of the photovoltaic can be easily separated at the end of the solar cell's lifetime.
"Organic solar cells must be recyclable," said lead author Bernard Kippelen in a statement at Georgia Tech, "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 life cycle."