Radiation testing indicates that solar cells composed of carbon-based, or organic, materials could be better than traditional silicon and gallium arsenide for producing electricity in the final frontier, according to a study from the University of Michigan published in Joule.
A simulation shows how deeply protons with higher energies of 100 kiloelectron-volt (keV) penetrate the solar cell. Solar wind protons can be accelerated to higher energies as they cross parts of the Earth’s magnetic field. At 100 keV, they can reach the glass backing of the solar cell. Image Credit: Yongxi Li, Optoelectronic Components and Materials Group, University of Michigan.
The new study also explored what occurs at the molecular level to result in performance declines, whereas earlier studies concentrated on how successfully organic solar cells converted light to electricity after radiation exposure.
Silicon semiconductors aren’t stable in space because of proton irradiation coming from the sun. We tested organic photovoltaics with protons because they are considered the most damaging particles in space for electronic materials.
Yongxi Li, Study First Author and Associate Research Scientist, Department of Electrical and Computer Engineering, University of Michigan
Gallium arsenide is frequently used on space missions due to its high efficiency and resistance to proton damage; nonetheless, it is costly, rather heavy, and rigid, much like silicon. Organic solar cells, on the other hand, are significantly lighter and can be flexible. Since space missions typically require extremely trusted materials, this study examines the reliability of organics.
After three years of exposure to radiation, organic solar cells comprised of tiny molecules appeared to be unaffected by protons. On the other hand, the efficiency of those created with polymers—more intricate molecules with branching structures—was cut in half.
We found that protons cleave some of the side chains, and that leaves an electron trap that degrades solar cell performance.
Stephen Forrest, Study Lead Corresponding Author and Peter A. Franken Distinguished University Professor, University of Michigan
These traps hold onto electrons that are released when light strikes the cell, stopping them from moving to the electrodes where the power is collected.
“You can heal this by thermal annealing, or heating the solar cell. But we might find ways to fill the traps with other atoms, eliminating this problem,” added Forrest.
At 100 °C (212 °F), it is conceivable that sun-facing solar cells might practically cure themselves; the warmth is sufficient to restore the bonds in the laboratory. However, there are still unanswered problems, such as whether that repair will still occur in the vacuum of space. For lengthy missions, is the healing sufficiently dependable? Designing the material to prevent the performance-destroying electron traps from ever occurring would be easier.
Li plans to pursue both options further as an incoming associate professor of advanced materials and manufacturing at Nanjing University in China.
Universal Display Corp and the US Office of Naval Research are funding the research.
The devices were partially manufactured at the Lurie Nanofabrication Facility, subjected to a proton beam at the Michigan Ion Beam Laboratory, and investigated at the Michigan Center for Materials Characterization.
The team applied for patent protection with the help of U-M Innovation Partnerships. Universal Display licensed the technology from U-M and filed a patent application. Forrest has a financial stake in Universal Display Corporation.
Journal Reference:
Li, Y., et al. (2025) Radiation hardness of organic photovoltaics. Joule. doi.org/10.1016/j.joule.2024.12.001