A miniature greenhouse prototype with a roof made from semi-transparent organic solar cells resulted in better plant growth than a traditional greenhouse. Photo: Yang Yang Laboratory/UCLA.
A miniature greenhouse prototype with a roof made from semi-transparent organic solar cells resulted in better plant growth than a traditional greenhouse. Photo: Yang Yang Laboratory/UCLA.

As countries around the globe seek sustainable energy sources and the US endeavors to become a net-zero emissions economy by 2050, renewable energy sources such as solar panels are in high demand.

However, solar panels can take up significant space and are often difficult to scale. Enter the new field of agrivoltaics, which focuses on the simultaneous use of land for both solar power generation and agriculture. For example, replacing the glass in greenhouses with solar panels could power the lamps and water controls in the greenhouse, or even the whole farm. But how does one build solar panels that can absorb energy from sunlight without blocking the light that plants need?

Materials scientist Yang Yang and his team in the Samueli School of Engineering at the University of California, Los Angeles (UCLA) have now designed just such a device. In a paper in Nature Sustainability, they report a new, viable application of solar cells that does not require large plots of land.

The team has developed a strategy for augmenting semi-transparent organic solar cells. These cells rely upon carbon-based materials, as opposed to the inorganic substances in conventional devices. The investigators incorporated a layer of a naturally occurring chemical called L-glutathione, which is sold as an antioxidant dietary supplement over the counter, into organic solar cells. They found that this addition extended the solar cells’ lifetime, improved their efficiency, and still allowed adequate sunlight to reach plants in a greenhouse prototype about the size of a small dollhouse.

“Organic materials are uniquely suitable for agrivoltaics because of their light-absorption selectivity,” said Yang, who also has a faculty appointment in bioengineering. “The main drawback that has prevented their widespread use up to now is their lack of stability."

Organic solar cells tend to degrade more quickly than their inorganic counterparts because sunlight can cause organic materials to oxidize and thus lose electrons. The researchers found that the additional layer of L-glutathione prevented the other materials in the solar cell from oxidizing. This resulted in the organic cells maintaining more than 80% efficiency after 1000 hours of continuous use – as opposed to less than 20% without the added layer.

The research team also tracked the growth of common crops including wheat, mung beans and broccoli in two different greenhouses. One had a transparent glass roof with segments of inorganic solar cells, while the other had a roof made entirely from semi-transparent organic solar cells. The team found that the crops in the greenhouse with the organic solar roof grew more than the crops in a regular greenhouse. They believe this was due to the L-glutathione layer blocking ultraviolet rays, which can inhibit plant growth, and infrared rays, which can cause greenhouses to overheat and the plants inside to require more water.

“We didn’t expect the organic solar cells to outperform a conventional glass-roof greenhouse,” said Yepin Zhao, the lead author of the research and a UCLA postdoctoral scholar in Yang’s lab. “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, especially in climates such as California’s, where sunlight is more abundant.”

On the heels of these findings, the team has established a startup at UCLA that aims to scale up production of the organic solar cells for industrial use. The researchers said they hope to make environmentally friendly greenhouses that incorporate the organic solar cells commercially available in the future.

This story is adapted from material from UCLA, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.