New way to boost solar cell efficiency by over 30 per cent

Researchers have found a simple and cheap way to modify the molecular structure of a polymer commonly used in solar cells, that can increase their efficiency by more than 30 per cent.
One of the most common ways to increase solar cell efficiency is by adding a fluorine atom to the polymer's molecular backbone, a difficult, multi-step process that can increase the solar cell's performance, but has considerable material fabrication costs.
A team of chemists led by Jianhui Hou from the Chinese Academy of Sciences created a polymer known as PBT-OP from two commercially available monomers and one easily synthesised monomer.

Wei Ma from North Carolina State University conducted the X-ray analysis of the polymer's structure and the donor-acceptor morphology.
PBT-OP was not only easier to make than other commonly used polymers, but a simple manipulation of its chemical structure gave it a lower highest unoccupied molecular orbital (HOMO) level than had been seen in other polymers with the same molecular backbone.
PBT-OP showed an open circuit voltage (the voltage available from a solar cell) value of 0.78 volts, a 36 per cent increase over the 0.6 volt average from similar polymers.

"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," co-author Harald Ade said.

"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," Ade said.
The study appears in the journal Advanced Materials.