Published on January 30th, 2013 | by James Ayre3
Super-Efficient Solar Cells Possible Through Use Of Exotic Form Of Silicon, Generating More Than One Electron-Hole Pair Per Photon
By utilizing an exotic form of silicon, silicon BC8, it is very likely possible to significantly raise the efficiency of solar cells, according to new research headed by the University of California, Davis.
Solar cells currently in use generate one electron-hole pair for every photon that hits them, and are capable of a theoretical maximum efficiency of ‘only’ 33%. But by utilizing nano-particles of an exotic form of silicon known as silicon BC8, it is possible for each photon to generate multiple electron-hole pairs.
“This approach is capable of increasing the maximum efficiency to 42%, beyond any solar cell available today, which would be a pretty big deal,” said lead author Stefan Wippermann, a postdoctoral researcher at UC Davis. “In fact, there is reason to believe that if parabolic mirrors are used to focus the sunlight on such a new-paradigm solar cell, its efficiency could reach as high as 70 percent.”
Silicon nano-particles, on their own, are capable of generating more than one electron-hole pair, because of an effect called “quantum confinement.”
“But with nanoparticles of conventional silicon, the paradigm works only in ultraviolet light,” Wippermann said. “This new approach will become useful only when it is demonstrated to work in visible sunlight.”
That’s where BC8 comes in, because of its ability to generate multiple pairs even with only visible light.
BC8 is a form of silicon that is formed under very high pressure but that remains stable at normal pressures, similar to the way that diamond is a form of carbon formed at extreme pressure but stable at normal ones.
“This is more than an academic exercise. A Harvard-MIT paper showed that when normal silicon solar cells are irradiated with laser light, the energy the laser emits may create a local pressure high enough to form BC8 nanocrystals. Thus, laser or chemical pressure treatment of existing solar cells may turn them into these higher-efficiency cells,” said co-author Gergely Zimanyi, professor of physics at UC Davis.
The new research was just published January 25th in the journal Physical Review Letters.
Source: University of California Davis (UCD)
Image Credits: Stefan Wippermann/UC Davis