I have been very reluctant to get on the bandwagon that nanotechnology offered us any clear, never mind easy, solutions to getting solar power to be more efficient in generating electricity.
But I am always willing to consider the possibility that nanotechnology holds the key to making cheap and highly efficient solar power. One of the nano-related alternatives I discussed was the use of quantum dots for either electron multiplication or creating so-called “hot-carrier” cells.
As I had explained previously, “Electron multiplication involves making multiple electron-hole pairs for each incoming photon while with hot carrier cells the extra energy supplied by a photon that is usually lost as heat is exploited to make in higher-energy electrons which in turn leads to a higher voltage.”
The concept of electron multiplication has been a line of research vigorously pursued since 2004 when it was first proposed. In my blog on the subject, I highlighted research coming from the University of Minnesota and Texas that had investigated further the possibility of creating multiple charge carriers from one photon.
But Eran Rabani, a researcher at Tel Aviv University, was not so convinced by the research on electron multiplication.
"Our theory shows that current predictions to increase efficiencies won't work,” Rabani is quoted as saying in the linked article above. “The increase in efficiencies cannot be achieved yet through Multiexciton Generation, a process by which several charge carriers (electrons and holes) are generated from one photon."
Rabani has published two articles on his research, one is in the journal Chemical Physical Lettersand the other in Nano Letters.
While Rabani seems to be dismissing this line of research and the possibility that more than one electron pair can be generated from one photon, he believes that by eliminating this line of research it will open up other research directions that are more promising for solar technology.
However, it’s not clear that this has permanently closed the door on Multiexciton Generation as Rabani quote seems to indicate: “The increase in efficiencies cannot be achieved YET through Multiexciton Generation.”
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.