The key to encouraging adoption of solar power, especially at the commercial scale, is increasing efficiency while reducing price. Solar panels have come a long way since the massive, bulky blocks that were on the market in the 1970s. Now, solar cells are thin, flexible, and even spherical, making it possible to imagine entirely new products that could be powered by the sun. The key to moving these products from concept to market is cost.
Now new research suggests that carbon nanotubes could be an efficient alternative for the expensive platinum electrodes in dye-sensitized solar cells (DSC). In combination with newly developed sulfide electrolytes, they could lead to more efficient and robust solar cells at a fraction of the current cost for traditional silicon-based solar cells, say a team of collaborative researchers at Rice University and Tsinghua University.
DSCs are sensitized with organic dyes absorb photons from sunlight and generate a charge in the form of electrons. This charge is usually captured by a semiconducting titanium oxide layer deposited on a current collector before flowing back to the counter electrode through another current collector. The single-wall nanotube arrays, which are grown through a process invented at Rice, are both much more electroactive and potentially cheaper than platinum, a common catalyst in DSCs, said Jun Lou, a materials scientist at the University.
By incorporating the nanotubes into solar cells, the scientists were able to achieve a power conversion efficiency of 5.25 percent – lower than the DSC record of 11 percent with iodine electrolytes and a platinum electrode, but significantly higher than a control test that combined the new electrolyte with a traditional platinum counter electrode.
“The carbon nanotube-to-current collector still has a pretty large contact resistance, and the effects of structural defects in carbon nanotubes on their corresponding catalytic performance are not fully understood, but we believe once we optimize everything, we’re going to get decent efficiency and make the whole thing very affordable,” Lou said. “The real attraction is that it will be a very low-cost alternative to silicon-based solar cells.”