Ann Arbor Times

Radiation testing indicates that organic solar cells, made from carbon-based materials, may surpass traditional silicon and gallium arsenide cells in space environments. A study by the University of Michigan explored how these organic photovoltaics respond to radiation at a molecular level, revealing potential advantages over existing technologies.

"Silicon semiconductors aren’t stable in space because of proton irradiation coming from the sun," said Yongxi Li, first author of the study published in Joule and former U-M associate research scientist. The research tested organic photovoltaics with protons, which are considered highly damaging particles for electronic materials in space.

Gallium arsenide is commonly used in space missions due to its efficiency and resistance to proton damage but comes with drawbacks such as cost and weight. Organic solar cells offer flexibility and lighter weight, prompting investigations into their reliability for space applications.

The study found that small molecule-based organic solar cells showed no damage after exposure equivalent to three years of radiation. However, polymer-based cells lost half their efficiency due to electron traps caused by proton-induced cleaving of side chains.

"We found that protons cleave some of the side chains, and that leaves an electron trap that degrades solar cell performance," said Stephen Forrest, lead corresponding author and Peter A. Franken Distinguished University Professor of Engineering at U-M.

These traps hinder electrons freed by light from reaching electrodes for electricity harvesting. Forrest noted possible solutions include thermal annealing or filling traps with other atoms.

While self-healing at 100°C (212°F) might be feasible under sunlight exposure in space, questions remain about its effectiveness in a vacuum environment during long missions. Designing materials without performance-degrading electron traps could be another solution.

Li plans further research on these possibilities as he joins Nanjing University as an associate professor.

The study received funding from Universal Display Corp and the U.S. Office of Naval Research. Devices were developed at various facilities including Lurie Nanofabrication Facility and Michigan Ion Beam Laboratory.

U-M Innovation Partnerships has filed for patent protection on behalf of the team. Universal Display has licensed this technology from U-M and applied for a patent. Forrest holds a financial interest in Universal Display Corp.