Plastic solar cells are now able to absorb a wider range of sunlight.
Recent scientific developments now allow plastic solar cells to compete with silicon-based solar cells in their ability to efficiently convert power. Experts are focused on increasing the net amount of photonic energies that plastic solar cells can absorb.
Initially, it was thought that ternary solar cells could offer a possible solution. These cells have been around for some time and involve the combination of three materials to create a light-harvesting layer. But the mixing process has proven difficult to perfect, and had never quite yielded the desired results.
Now, a team of researchers from North Carolina State University, led by graduate student Masoud Ghasemi, have devised a new strategy for fabricating much more efficient plastic solar cells. Ghasemi worked alongside a team of physicists led by Harald Ade, along with a team of chemists from University of North Carolina at Chapel Hill led by Wei You.
The team analyzed the ternary method using two absorption-matched donor polymers and a fullerene acceptor as a calorimetric tool. As predicted, the old method of mixing all three materials together and depositing them yielded a poor performance.
Said Ghasemi, “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. This explains why so many conventionally produced ternary cells may have low efficiency.”
To solve the alloying issue, the team began mixing each polymer with fullerene separately, as opposed to all together simultaneously. This process generated two different mixtures they then laid onto the substrate, yielding sequentially cast ternary solar cells (SeCaT) which did not alloy.
“The SeCaT solar cells prevent the polymers from mixing due to their layered structure. 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,” said Ghasemi. “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 to these applications.”