Organic solar cells help plants in greenhouses grow better, finds study

Researchers at the Samueli School of Engineering at the University of California, Los Angeles (UCLA) have developed solar cells using organic components and deployed them in greenhouses to demonstrate a use case in agrivoltaics.

With nations around the world looking for ways to move away from fossil fuels, solar energy is one of the renewable energy sources everybody is looking to tap into. However, the deployment of large solar farms is competing with the need to feed the growing global population. This is where the field of agrivoltaics comes in.

The method allows for the dual use of the available land and allows for the generation of solar-based energy along with agriculture. The field is still in its infancy, and further innovations are needed to make it mainstream. Organic solar cells could be one such innovation.

Making solar cells from organic components

Conventionally, solar cells are made from inorganic substances such as silicon that do not decay easily and are considered one of the future problems humanity will have to deal with in a few decades.

A research team led by Yang Yang, a material scientist at UCLA, turned to organic materials, i.e., those having carbon as one of the components to make solar cells instead. This method, however, has a drawback in that incident sunlight causes oxidation of the organic components, leading to their decay and significantly dropping their efficiency.

Yang and his team turned to another naturally occurring material, L-glutathione, to add a layer to the organic solar cells to overcome this. Sold as an over-the-counter, antioxidant dietary supplement, the L-glutathione layer prevented the materials from undergoing oxidation and maintained their efficiency, even after 1,000 hours of continuous use.

To test their semi-transparent organic solar cells, the researcher used them in small greenhouse prototypes where they also grew crops like wheat, mung beans, and broccoli. To demonstrate the efficiency of the cells, the researchers used a control greenhouse prototype that used inorganic or conventional solar cells. The researchers found that the crops in the greenhouse with organic solar cells grew more than those in the regular greenhouse.

"We didn’t expect the organic solar cells to outperform a conventional glass-roof greenhouse,” said Yepin Zhao, a member of Yang’s lab at UCLA, in a press release. “But we repeated the experiments multiple times with the same results, and after further research and analysis, we discovered that plants don’t need as much sunlight to grow as we’d originally thought. In fact, too much sun exposure can do more harm than good."

The researchers also suspect that the layer of L-glutathione blocked ultraviolet (UV) and infrared (IR) rays from reaching the plants. The UV rays can inhibit plant growth, while IR can heat up a greenhouse, increasing plants' water requirement. Neither happened in the greenhouse with organic solar cells.

The research findings were published in the journal Nature Sustainability.