The Power of Plastic: Improved Plastic Solar Cells Absorb More Energy

Solar cells have been steadily gaining popularity because of the environmental and financial benefits. This technology is continuously being improved by researchers, such as the team from North Carolina State University who have discovered a new method to improve the efficiency of plastic solar cells.

With plastic solar cells now competing with solar cells made from silicon in terms of their efficiency in converting power, the research team wanted to extend the range of photonic energies plastic solar cells could absorb. The lead author of the paper published in Advanced Materials, Masoud Ghasemi, wanted to produce solar cells with a wider absorption range and greater efficiency. A graduate student in physics at North Carolina State University, Ghsemi worked with a team of other North Carolina State University physicists headed by Harald Ade as well as chemists from the University of North Carolina at Chapel Hill led by Wei You to achieve this goal.

Ternary solar cells have been in production for years. But due to unfavorable mixing, this mixture of three materials that forms a light-harvesting layer haven't been performing as well as scientists had hoped. A calorimetric tool was proposed by the researchers to study the morphology of a ternary system with two absorption-matched donor polymers and a fullerene acceptor. The traditional method of combining all three materials and then depositing them onto a substrate yielded poor results.

"Using thermodynamic techniques, we were able to find that this particular mixture was undergoing 'alloying,' in which the donor polymers tend to group up together and push the fullerene away," Ghasemi explained. "This explains why so many conventionally produced ternary cells may have low efficiency."

Ghasemi and his team proposed a solution: mix each polymer separately with the fullerene, rather than mixing all three materials together at once. This would then yield two separate mixtures that were layered onto the substrate, creating sequentially cast ternary (SeCaT) solar cells. To the researchers' delight, this method was not prone to alloying.

"The SeCaT solar cells prevent the polymers from mixing due to their layered structure," Ghasemi shared. "This novel design allows fabrication of plastic solar cells with wider optical sensitivity using cheap and scalable processing steps and with reduced materials selection constraints. Hopefully, this new method can be particularly useful for greenhouse applications toward zero energy farming, as the materials used to demonstrate our method have optical properties compatible with applications."