In the past, I have tried to dispel the myth that nanotechnology could be waved over alternative energy applications to make them suddenly much more economically viable than they have been. In these efforts, I have even gone so far as to question the reasoning of Nobel Laureates in Economics on why we are not further along in the development of photovoltaics.
This is not to say that nanotechnology is not improving various alternative energy solutions, in particular photovoltaics. But the process of bringing these technologies to market is much slower than many people seem willing to tolerate and their announcements should be taken with a grain of salt...and patience.
So, it is with some cautious optimism I alert you to research coming out of Northwestern University in which the researchers claim to have developed a new type of solar cell that has all the benefits of the Grätzel cell (or dye-sensitized solar cell (DSSC)) without the short life expectancy.
“The Grätzel cell is like having the concept for the light bulb but not having the tungsten wire or carbon material,” explains one of the researchers, Mercouri Kanatzidis, in the university’s press release covering the development. “We created a robust novel material that makes the Grätzel cell concept work better. Our material is solid, not liquid, so it should not leak or corrode.”
This is not the first time that researchers have attempted to find a replacement for the organic liquid that makes up the electrolyte in DSSCs. But previous attempts have resulted in solar cells with poor energy conversion efficiency. To overcome this Kanatzidis and his colleague Robert P.H. Chang used a thin-film compound made up of cesium, tin and iodine, which serves as a p-type direct bandgap semiconductor. Details of the new material can be found in their recently published article in Nature. The result is the Northwestern solar cell reached a conversion efficiency of 10.2 percent, in the neighborhood of the 11 to 12 percent reached by the best performing Grätzel cell.
“This is the first demonstration of an all solid-state dye-sensitized solar cell system that promises to exceed the performance of the Grätzel cell,” Chang is quoted as saying in the same university press release. “Our work opens up the possibility of these materials becoming state of the art with much higher efficiencies than we’ve seen so far.”
While the university press release quotes Chang as saying that their solar cell is “inexpensive,” there were no accompanying cost calculations to back up the claim. Last year, when I spoke to Michael Grätzel, the discoverer of the DSSC, we talked not of lifecycle costs, but about boosting the conversion efficiency of the DSSC. But perhaps more important than conversion efficiency, the key metric for Grätzel was the kWh price.
From my discussion with Grätzel in Budapest last May:
When it came to the question of conversion efficiency, Dr. Grätzel seemed resigned to the percentage game that seems to exist, but believed that kilowatt hour (kWh) to price was a more significant metric.
“We have to play the game. We have to go and have our efficiencies validated by an accredited PV calibration laboratory. We cannot create a different world where we just say we are the best,” he said. “We are living exactly with the standards that silicon has set in terms of efficiency and stability.
“But, on the other hand, it is true that when it comes to the advantages we should also play those up as well,” he said. He added that under certain outdoor exposures DSSC will already out perform silicon in the key metric of kWh price
“In the end, what we would really like to see is kWh price used as a metric in addition to peak watt price. The peak watt price is a good standard but when it comes to outdoor applications it often does not reflect reality such as the performance under cloudy conditions and the drop of conversion efficiency with temperature encountered by silicon solar cells,” he said.
It may be that the Northwestern researchers have developed a solar cell that when you calculate life cycle costs (presumably since they last longer they don't have to be replaced as often) has a better kWh cost than any other solar cells on the market, including the Grätzel cell. But I would like to see those calculations before I pronounce this as the replacement for any solar cell.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.