A research team found that by manipulating the structure of polymers within the solar cell they could increase its efficiency by 30 percent, a North Carolina State University news release reported.
Solar cells that are polymer-based possess two “domains,” one is an electron acceptor and the other an electron donor material.
Excitons (“the energy particles created by solar cells when light is absorbed”) must be able to “travel quickly to the interface of the donor and acceptor domains and retain as much of the light’s energy as possible” in order to be effectively utilized.
Researchers can increase the efficiency of solar cells by adjusting the difference between the “highest occupied molecular orbit” (HOMO) and the “lowest unoccupied molecular orbit” (LUMO) polymer levels, this allows the exciton to be harnessed with minimal energy loss.
The polymer levels can be adjusted by inserting a fluorine atom into the polymer’s “molecular backbone.” The problem is this method is extremely difficult and comes with significant “material fabrication costs.”
Chemists from the Chinese Academy of Sciences were able to create a polymer, dubbed PBT-OP, from two monomers that are commercially available and one that is easy to create. The team then performed an X-ray analysis of the polymer that looked at its structure and “donor:acceptor morphology.”
PBT-OP was easier to make than most polymers; a “simple manipulation” allowed the researchers to lower the HOMO level while maintaining the polymer’s molecular backbone.
“PBT-OP showed an open circuit voltage (the voltage available from a solar cell) value of 0.78 volts, a 36 percent increase over the ~ 0.6 volt average from similar polymers,” the news release reported.
“The possible drawback in changing the molecular structure of these materials is that you may enhance one aspect of the solar cell but inadvertently create unintended consequences in devices that defeat the initial intent,” NC State physicist and co-author Harald Ade said in the news release. “In this case, we have found a chemically easy way to change the electronic structure and enhance device efficiency by capturing a lager fraction of the light’s energy, without changing the material’s ability to absorb, create and transport energy.”
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