Researchers from the New York University (NYU) Tandon School of Engineering have come up with what they call an innovative and promising way to improve solar cells.
Tandon Associate Professor André D. Taylor of the Chemical and Biomolecular Engineering Department led the team of researchers on the project.
Most organic solar cells use fullerenes, spherical molecules of carbon, explains a Tandon press release. The problem, according to Taylor, is that fullerenes are expensive, and they don’t absorb enough light.
Over the last 10 years, Taylor has made significant progress in improving organic solar cells, and he has recently focused on using non-fullerenes, which, until now, have been inefficient, explains Tandon.
However, Taylor says, “The non-fullerenes are improving enough to give fullerenes a run for their money.”
Think of a solar cell as a sandwich, Taylor says. The “meat,” or active layer – made of electron donors and acceptors – is in the middle, absorbing sunlight and transforming it into electricity (electrons and holes), while the “bread,” or outside layers, consists of electrodes that transport that electricity.
Taylor’s team’s goal was to have the cell absorb light across as large a spectrum as possible using a variety of materials, yet at the same time, allow these materials to work together well.
“My group works on key parts of the ‘sandwich,’ such as the electron and hole transporting layers of the ‘bread,’ while other groups may work only on the ‘meat’ or interlayer materials. The question is, how do you get them to play together? The right blend of these disparate materials is extremely difficult to achieve.”
Using a squaraine molecule in a new way – as a crystallizing agent – did the trick, says Tandon.
“We added a small molecule that functions as an electron donor by itself and enhances the absorption of the active layer,” Taylor explains. “By adding this small molecule, it facilitates the orientation of the donor-acceptor polymer (called PBDB-T) with the non-fullerene acceptor, ITIC, in a favorable arrangement.”
This solar architecture also uses another design mechanism that the group pioneered, known as a FRET-based solar cell. FRET, or Förster resonance energy transfer, is an energy transfer mechanism first observed in photosynthesis, by which plants use sunlight, the university explains.
Using a new polymer and non-fullerene blend with squaraine, the team converted more than 10% of solar energy into power. Just a few years ago, this was considered too lofty a goal for single-junction polymer solar cells, says Tandon.
“There are now newer polymer non-fullerene systems that can perform above 13 percent, so we view our contribution as a viable strategy for improving these systems,” Taylor explains.
The organic solar cells developed by his team are flexible and could one day be used in applications supporting electric vehicles, wearable electronics or backpacks to charge cell phones, according to the school. Eventually, they could also contribute significantly to the supply of electric power.
“We expect that this crystallizing-agent method will attract attention from chemists and materials scientists affiliated with organic electronics,” says Yifan Zheng, Taylor’s former research student and lead author of the article about the work in the journal Materials Today.
Next for the research team? They are working on a type of solar cell called a perovskite, as well as continuing to improve non-fullerene organic solar cells, says Tandon.
“A Highly Efficient Polymer Non-Fullerene Organic Solar Cell Enhanced by Introducing a Small Molecule as a Crystallizing-Agent” is available at ScienceDirect.
In addition to Taylor and Zheng, co-authors are Jiang Huang and Junsheng Yu of the University of Electronic Science and Technology of China; Gang Wang of Northwestern University; Jaemin Kong, a post-doctoral researcher now at NYU; and Di Huang, Megan Mohadjer Beromi and Nilay Hazari of Yale. The National Natural Science Foundation of China, the Project of Science and Technology of Sichuan Province, the U.S. National Science Foundation, and the Yale Institute for Nanoscience and Quantum Engineering supported the research.