You’ve probably noticed solar panels sprouting on rooftops in your neighborhood. Solar panels are made out of multiple solar cells, which are commonly manufactured out of silicon, the same material in sand. When sunlight hits a solar panel, electrons in the silicon get agitated and flow through wires built into the panel, making electricity.
Solar panels on roofs are now commonplace. But have you spotted any backpacks sporting solar cells? They’re made out of organic materials - commonly polymers, or plastics, for absorbing light and transporting electrical charges.
Organic solar cells are the latest in solar technology. They promise to be cheaper to mass produce for large-area devices, they have low environmental impact and, since they are compatible with flexible substrates, they could be used in novel applications such as clothing, bendable screens and packaging.
Unfortunately, solar cells made from organic materials are less efficient. Another problem is that they can deform a bit in the hot sun, which affects their electrical properties. For organic solar cells to really work, they will need to be made more efficient and to be made more stable to withstand significant changes in conditions.
NSLS, used cooperatively with Brookhaven Lab’s Center for Functional Nanomaterials, is helping to improve organic solar cells.
Scientists have discovered that one way to increase the stability of solar cells made out of organic polymer is to lock in place the semiconducting base layer, the first layer upon which the solar cell is built. To do this, a chemical “crosslinker,” which interconnects the polymer chains in the material’s base layer, is added to the solution-based starting materials. This is like chemically freezing the polymer to make it more stable.
In addition to stabilizing the polymer, the crosslinker also increases its conductivity by as much as five times. X-ray measurements at NSLS show that the addition of the crosslinker causes the polymer chains to orient in a way that allows the electrons to flow more directly.
Working together, scientists at NSLS and the Center for Functional Nanomaterials make model solar cells in the nanocenter and then analyze them using complementary tools in both facilities. This research is funded by the U.S. Department of Energy.