A new approach to designing more durable solar panels from organic materials that makes harvesting energy in space more efficient and lasts for longer periods than panels made from polymer-based materials has the University of Michigan (U-M) scientists behind its discovery applying for a patent.
Solar panels currently used for harvesting energy in space lose efficiency over time due to damage caused by proton radiation from the sun. Unfortunately, materials used to protect the panels from this specific type of damage can be costly and add significant weight to space missions where weight is at a premium.
Now, thanks to funding from the U.S. Office of Naval Research, the panels designed by the Michigan scientists proved uniquely capable of resisting this damage in lab tests. The scientists say their results are fueling optimism that the organic approach could reduce launch costs and extend mission times for spacecraft powered by solar energy.
The Heavy Costs of Harvesting Energy in Space
Due to the significant time and expenses associated with sending missions into space, many satellites and spacecraft use the energy from the sun to power the mission once it is in orbit or en route to another solar system destination. And while space-based solar panels don’t suffer from performance reduction due to bad weather or dust like Earth-based panels, they encounter significantly higher amounts of solar radiation.
“Silicon semiconductors aren’t stable in space because of proton irradiation coming from the sun,” explained Yongxi Li, first author of the study and a U-M associate research scientist in electrical and computer engineering at the time of the research.
According to a statement from the U-M team, this proton bombardment causes small cracks to form within traditional panels made from polymers instead of organic materials. These cracks result in a series of electron “traps” that rob the panel of some of its ability to harvest energy in space. The more time passes, the more pronounced the efficiency reduction becomes.
“We found that protons cleave some of the side chains, and that leaves an electron trap that degrades solar cell performance,” explained the study’s lead corresponding author, Stephen Forrest, the Peter A. Franken Distinguished University Professor of Engineering at U-M.
When it Comes to Solar Panels, Organic Don’t Crack
To counteract the effect, the team turned toward organics. Specifically, the team designed and tested customized solar panels made from organic materials that they hoped would resist cracking due to proton irradiation. The team also hoped their panels would be lighter and more flexible than the silicon and gallium arsenide panels favored by mission planners due to their resistance to protons.
“We tested organic photovoltaics with protons because they are considered the most damaging particles in space for electronic materials,” Li explained.
As hoped, the material proved significantly more resistant than traditional polymer-based panels. Conversely, the conventional panels tested by the team showed significant damage and a correspondingly dramatic reduction in efficiency.
“Organic solar cells made with small molecules didn’t seem to have any trouble with protons—they showed no damage after three years’ worth of radiation,” the scientists explained. “In contrast, those made with polymers—more complex molecules with branching structures—lost half of their efficiency.”
Scientists Apply for Patent While Continuing Research
The U-M researchers have already applied for a patent on their new approach to harvesting energy in space. They have also partnered with Universal Display Corp, an OLED design company that has licensed their organic solar panel technology and is filing a separate technology patent.
While awaiting their patent, the team says they continue researching methods for improving the longevity and performance of harvesting energy In space while reducing mission costs. According to Forrest, one approach might involve methods designed to “heal” the cracks that appear in solar panels.
“You can heal this by thermal annealing or heating the solar cell,” the professor explained, “by raising its overall temperature” to 100°C (212°F). While this process works in the lab, the team says they are unsure whether or not the same self-healing will occur in space. They also don’t know how long a solar cell “repaired” in this matter will work, a critical variable in missions with a longer duration.
Ultimately, the team feels the solution may involve designing a solar panel that resists this damage in the first place, such as their organic panel approach. Li says he will continue investigating both approaches in his new position at Nanjing University in China. In contrast, Forrest says his team may find ways to fill the proton traps with other items, “eliminating this problem.”
The study “Radiation hardness of organic photovoltaics” was published in Joule.
Christopher Plain is a Science Fiction and Fantasy novelist and Head Science Writer at The Debrief. Follow and connect with him on X, learn about his books at plainfiction.com, or email him directly at christopher@thedebrief.org.