Carbon nanotube solar cells point to possible transparent solar window future

Imagine if every window of the 828-meter (2,717-foot) high Burj Khalifa in Dubai was capable of generating electricity just like a PV panel. That's the promise of solar window technology like the RSi and Sphelar cells systems. Rather than using costly silicon for window-based collection of solar energy, Dr Mark Bissett proposes using a very thin layer of carbon nanotubes instead. As part of his PhD at the Flinders University School of Chemical and Physical Sciences, Dr Bissett has developed a proof of concept prototype solar cell that is made up of two sheets of electrically-conductive glass with a layer of functionalized, single-walled carbon nanotubes sandwiched between them. As the nanotube layer is only between 100 - 200nm thick and the two sheets of glass are just 60µm apart, the cell remains transparent - letting some natural light flow through while also collecting energy from the sun. "When light shines on the cell, electrons are generated within the carbon nanotubes and these can be used to power electrical devices," said Dr Bissett. "It's basically like tinting the windows except they're able to produce electricity, and considering office buildings don't have a lot of roof space for solar panels, it makes sense to utilize the many windows they do have instead."

Unfortunately, the cells have yet to be tested outside of the laboratory and work is still needed to improve the efficiency of the technology before being scaled up to an industrial level. Dr Bissett told us that the trade-off between transparency and the ability to harvest light means that even the best cells in the lab are only just approaching 1% efficiency. There is a way around this, but it comes at a cost. "Basically by decreasing transparency you can increase efficiency," explained Dr Bissett. "In comparison, other new solar cell technologies like dye-sensitized solar cells are close to 10% and silicon solar cells tend to be around the 20% mark, depending on the exact technology used to produce them. So work is still needed on increasing the efficiency of our designs to make them competitive, but it is still early days for this technology with many possible research avenues to pursue." Dr Bissett has also successfully demonstrated that the carbon nanotube layer can be spray-coated onto glass, which would allow for larger areas of glass substrate to be functionalized. The next step in the development process is to test the technology in the real world. He believes that if all goes to plan, the new technology could be on the market within the next ten years. "This research is still being pursued by the research group I worked with at Flinders University with Professor Joe Shapter," he said. "There is also work being undertaken to produce flexible solar cells based on graphene, these are of interest for integration into fabrics." Meanwhile Dr Bissett is currently undertaking a post-doctorate at Kyushu University, Japan.