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A team of scientists from Rice University, Houston Community College and Brookhaven National Laboratory has developed flexible organic photovoltaic systems that could be useful in cases where constant, low-power production is sufficient.
Mok et al developed flexible organic photovoltaic systems with a chemical additive that mitigates the fragile qualities of the material without loss of efficiency. Image credit: Jeff Fitlow / Rice University.
Organic solar cells use carbon-based materials, including polymers, as opposed to hard and inorganic materials such as silicon, to capture sunlight and translate it into current. Organic products are also thin, light, semi-transparent and inexpensive.
While the commercially used silicon-based intermediate solar cells have a yield of about 22%, the organic materials reach about 15%.
"The efficiency of these devices has increased, but the mechanical properties are also very important. If you stretch or bend objects, you get cracks in the active layer and the device breaks down, "said team leader Rafael Verduzco, a researcher in the Department of Chemical and Biomolecular Engineering and Department of Science. materials and nanotechnology at Rice University.
"One solution to solving the fragile problem would be to find polymers or other flexible organic semiconductors by nature, but his lab chose another approach."
"Our idea was to stick with carefully developed materials over the last 20 years, which we know are working, and find ways to improve their mechanical properties."
Rather than creating a mesh and pouring semiconductor polymers, Dr. Verduzco and his co-authors mixed sulfur-based thiol-ene reagents. The molecules mix with the polymers and then crosslink with each other to provide flexibility.
The process is not gratuitous, because too little thiol-ene leaves the crystalline polymers subject to stress cracking, while too much lessens the effectiveness of the material.
"If we replaced 50% of the active layer with this mesh, the material would get 50% less light and the current would drop," said Dr. Verduzco.
"At some point, it's not practical. Even after confirming that the network was forming, we needed to determine the amount of thiol-ene needed to remove the fracture and the maximum we could put without making it useless as an electronic device. "
At approximately 20% thiolene, the team found that the cells retained their effectiveness and gained flexibility.
The next step was to stretch the fabric.
"Pure P3HT (the polythiophene-based active layer) started to crack with a deformation of about 6%," said Dr. Verduzco.
"When we added 10% thiolene, we could filter it up to 14%. At about 16% of the load, we started to see cracks throughout the material. "
At stresses greater than 30%, the material buckled very well but became useless as a solar cell.
"We did not see any loss of photocurrent up to about 20%. That seems like the right choice, "said Dr. Verduzco.
The study is published in the journal Materials chemistry.
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Jorge Wu Mok et al. Organic photovoltaic system with heterojunction in mass stabilized network. Chem. mate, published online October 26, 2018; doi: 10.1021 / acs.chemmater.8b03791
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