Researchers at the Georgia Institute of Technology and Purdue University have indeed developed solar cells that use natural substrates derived from trees. Equally important in producing these solar cells on substrates of cellulose nanocrystals (CNC), they have the ability to be rapidly degraded in water at end of cycle.
The researchers said their organic solar cells reached a conversion efficiency of about 2.7%, an unprecedented figure for cells on substrates made from renewable raw materials.
The substrates on which the solar cells are made transparent remain, which allows light to pass through before it is absorbed by a thin layer of an organic semiconductor. During the recycling process, the solar cells are simply immersed in water at room temperature. In just minutes, the substrate is dissolved and the solar cell can be easily separated from its main components.
For Professor Bernard Kippelen who led the study, this project opens the door to a solar cell technology really “recyclable”, “sustainable” and “renewable”.
“The development and performance of organic substrates are constantly improving, providing engineers with a good indication of future applications,” he added. “But organic solar cells need to be recycled. Otherwise, we solve one problem, namely, less dependence on fossil fuels while creating another, a technology that produces energy from to a renewable source, but is a waste at the end of its life cycle.”
Currently, organic solar cells are designed to glass or plastic. Neither is easily recyclable. For example, if solar cells fabricated on glass were to break during phases of manufacture or installation, the materials become useless become difficult to remove. Paper substrates are better for the environment, but they have shown limited performance due to the roughness of the high porosity of the surface. However, nanomaterials made from wood cellulose are “recycling”, “renewable” and “sustainable”. The substrates have a low surface roughness of only 2 nanometers.
“Our next step is to work on improving the efficiency of power conversion at rates exceeding 10%, similar to levels produced on glass substrates or petroleum-based solar cells,” said Bernard Kippelen. The team aims to achieve this by optimizing the optical properties of the electrode of the solar cell. “We will also take these cells with a protective coating to protect them from water and oxygen when operated on the ground.”