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Trees sprout a new branch of photovoltaics

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We’ve all heard the phrase “make like a tree and leave,” right? Well, researchers from Imperial College London’s Clean Energy Processes program are taking this saying to the next level by looking toward nature in a bid to increase efficiency in solar energy production. Their solution: a handmade photovoltaic (PV) leaf to precisely imitate the real deal.

Most commercial PV panels convert solar into electrical energy with only 25% efficiency or less, according to the researchers, who also said that >70% of solar energy that is incident on a cell is dissipated as heat. This heat leads to the deterioration of not only the panel’s performance but also its overall service lifetime. This led the researchers to search for a more effective solar cell that can more adequately regulate heat. To do this, they looked toward nature’s solar panels for an answer.

Courtesy of Dr. Gan Huang, Imperial College London.


Courtesy of Dr. Gan Huang, Imperial College London.

They were able to fabricate a synthetic version of a leaf’s three-layer structure to mimic the transpiration process of organic foliage, which allows the water within a leaf to distribute through capillaries to the surface, where it evaporates and effectively cools the leaf as it converts sunlight to energy. The researchers’ prototype measures 1.5 mm thick with dimensions of 10 × 10 cm, with a biomimetic transpiration (BT) layer sandwiched between a PV cell layer above and a supportive molecular mesh below. Delving further into nature, the researchers incorporated bamboo fibers into the BT layer to imitate the water-transporting capillaries of a real leaf. The fibers moved water to the molecular mesh layer where it could cool the synthetic leaf through evaporation, while still allowing for the possibility of being re-collected.


Comparing the PV leaf with the conventional PV cells, it reached a temperature of 43.2 °C versus the standard cell temperature of 68.8 °C. Not only that, but the researchers found that the transpiration rate increased significantly as the PV leaf’s operating temperature increased, which allowed for effective control of its temperature and contributed to the stabilization of this temperature after a short transient. Most importantly, the electrical efficiency of the PV leaf was 13.6% higher than that of the standalone PV cell.

Another sunny feature of the synthetic leaf is its ability to recycle water. Although the researchers originally tested its transpiration process using fresh water, in acknowledgment of the frequent shortage of fresh water, they later explored whether saline would work as well. Not only did the saline work comparably well, but it also saw a production of 1.1 L/h/m2 of fresh water under a solar irradiance of 1000 mW/m2 while improving the electrical efficiency of the device by ~10%. Effectively, the PV leaf runs better on seawater while converting it into fresh water and simultaneously provides bountiful electricity at lower material costs. Perhaps we should look to the trees more often for our energy solutions!

The research was published in Nature Communications (https://doi.org/10.1038/s41467-023-38984-7).


Courtesy of iStock.com/Tetiana Garkusha.

Published: October 2023
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