The new investigation uncovered what happens at the molecular level to cause drops in performance. Previous research also focused on how well organic solar cells converted light into electricity following radiation exposure.
“Silicon semiconductors aren’t stable in space because of proton irradiation coming from the sun,” said Yongxi Li, first author of the study to be published in Joule and a U-M associate research scientist in electrical and computer engineering at the time of the research. “We tested organic photovoltaics with protons because they are considered the most damaging particles in space for electronic materials.”
Space missions tend to use Gallium. Though highly efficient and resistant to proton damage, is Gallium expensive, heavy and inflexible.
Organic solar cells are more flexible and lighter. They are made with small molecules that do not seem to have any trouble with proton damage. But cells made with polymers—more complex molecules with branching structures—lost half of their efficiency.
“We found that protons cleave some of the side chains, and that leaves an electron trap that degrades solar cell performance,” said Stephen Forrest, the Peter A. Franken Distinguished University Professor of Engineering at U-M, and lead corresponding author of the study.
These traps grab onto electrons freed by light hitting the cell, preventing them from flowing to the electrodes that harvest the electricity.
“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,” Forrest said.
The research is funded by Universal Display Corp and the U.S. Office of Naval Research.
