Organic Solar Cells to Power Smart Greenhouses

Greenhouse prototype

A miniature greenhouse prototype with its roof built of semi-transparent solar cells invented by materials scientists at the University of California, Los Angeles (UCLA) that resulted in better plant growth than a traditional greenhouse. [Image: Yang Yang Laboratory / UCLA]

Climate change—which brings more intense periods of heavy rain, longer dry periods and extreme heat—threatens both farmers’ livelihoods and the world’s food supply. One potential solution for farms is the use of greenhouses to regulate the environment and boost crop yields.

Now researchers in the United States have designed a smart greenhouse with semi-transparent organic solar cells integrated into its roof (Nat. Sustain., doi: 10.1038/s41893-023-01071-2). The addition of an interlayer based on L-glutathione improved the solar cells’ lifetime and efficiency, while also promoting crop growth by blocking ultraviolet rays.

More sustainable, resilient farms

Agriculture is one of the most climate-sensitive industries, with farmers and farm communities being increasingly vulnerable to changing precipitation and temperature patterns. Reductions in agricultural productivity due to climate change will likely lead to increased food prices and greater food insecurity.

With support from the California Energy Commission, Yang Yang at the University of California, Los Angeles, and his colleagues aimed to create new technologies to help make farming operations more sustainable and resilient in the face of climate change. Specifically, they delved into the emerging field of agrivoltaics, or the use of land for both agriculture and solar power generation.

“One of the problems of solar energy is the amount of land needed. Often times, agriculture and the energy industry are fighting for limited land,” said Yang. “Our technology can address both demands simultaneously.”

Adding another layer

Semi-transparent organic photovoltaics have several advantages, such as being lightweight, low cost and flexible. However, the devices have lingering issues with operational stability that prevent widespread use on roofs and windows. In the presence of sunlight, radicals generated by the zinc-oxide electron-transport layer degrade the organic molecules in the photoactive layer.

To address this issue, the team added a reductive interlayer based on reduced L-glutathione to prevent direct contact between the electron-transport layer and the photoactive layer. The resulting organic cells had a power-conversion efficiency of 13.5% and an average visible transmittance of 21.5%. The stability improved dramatically, with the devices maintaining 84.8% efficiency after 1,008 hours of continuous use, as opposed to less than 20% without the interlayer.

The researchers built miniature greenhouse prototypes fitted with a roof of semi-transparent organic solar cells to test their impact on common crops (mung bean, wheat and broccoli). In terms of sprout length and survival rate, sprouts grown in greenhouses with organic cells did as well or better compared to those grown in greenhouses with glass or inorganic solar cells.

Less heat, less water

Yang speculates that the observed benefits to the crops may stem from the L-glutathione layer blocking ultraviolet rays that can inhibit plant growth, as well as infrared rays, which can cause greenhouses to overheat. He notes that, because of the latter, crops grown in greenhouses with organic cell roofs required less water than their counterparts.

“We are going to make the solar panels in a larger size, and we’d like to work with a greenhouse company to see whether we can come up with a practical application for their product,” Yang said. “We want to commercialize the technology by working with industrial partners.”

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