Inexpensive photovoltaic materials based on polymers rather than silicon could ultimately be made more efficient through a relatively simple molecular tweak according to UK researchers. [Nelson et al., Nature Mater., (2016), DOI: 10.1038/nmat4645]

Jenny Nelson of Imperial College London and colleagues point out that polymers are yet to usurp silicon despite being cheaper, less dense and easier to produce. Key to making these materials more efficient is to look at extending the range of light they can absorb rather than focusing on the red end of the spectrum as has been the wont of other research.

"When searching for better solar cell materials, chemists usually focus on changing the chemical structure of materials in order to capture more infrared or red light," Nelson explains. Writing in Nature Materials, she and graduate student Michelle Vezie and their colleagues, demonstrate an alternative to creating more absorptive and so more efficient polymer solar panels. "We found a material that absorbed more light despite no change in the chemical structure of its light-absorbing regions, so we decided to investigate why that might be; the results were really quite surprising," Nelson adds.

The collaboration involved scientists from Barcelona's CSIC, the University of Cyprus, University College London, and King Abdullah University of Science and Technology in Saudi Arabia, and has found that the new polymers could absorb up to 50 percent more light than conventional materials because they can stretch out in the sun. Extension seems to be partly responsible for absorption. Tests showed that the more rigid polymers made the more efficient photovoltaic materials.

"I tend to think of it like a radio aerial," explains team member Sheridan Few, "if your aerial is bent out of shape, it's not going to receive a signal very well. Similarly, if the polymer chains in a solar panel are not aligned straight, that material won't absorb light very well. This mechanical property of rigidity can be quantified in terms of the polymer's 'persistence length'."

Intriguingly, the team went back and tested some older polymers that had been discounted as poor absorbers and found that if they could make them more rigid and so get better alignment, they could improve efficiency. Of course, lack of conductivity in polymers when compared to silicon remains an obstacle yet to be overcome. However, by analyzing persistence lengths the team is taking a step towards plastic solar cells and is hoping that other researchers and companies will work with them to shed more light on this area of energy conversion.

David Bradley blogs at Sciencebase Science Blog and tweets @sciencebase, he is author of the popular science book "Deceived Wisdom".