UC Davis, Hungary develop new, more efficient PV cell

Researchers at the University of California, Davis, and in Hungary have found that using an exotic form of silicon could substantially improve the efficiency of solar photovoltaic (PV) cells.

The researchers performed computer simulations and their work was published on January 25th, 2013, in the journal “Physical Review Letters”.

Conventional solar cells generate one electron-hole pair per incoming photon, and have a theoretical maximum efficiency of 33%. One exciting new route to improved efficiency is to generate more than one electron-hole pair per photon, stated Giulia Galli, professor of chemistry at UC Davis and co-author of the paper.

Maximum efficiency could be increased to 42%

"This approach is capable of increasing the maximum efficiency to 42%, beyond any solar cell available today, which would be a pretty big deal," stated 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%," Wippermann added.

The researchers simulated the behavior of a structure of silicon called silicon BC8, which is formed under high pressure but is stable at normal pressures, much as diamond is a form of carbon formed under high pressure but stable at normal pressures.

The computer simulations were run through the National Energy Research Scientific Supercomputing Center at the Lawrence Berkeley Laboratory, which granted the project 10 million hours of supercomputer time.

The simulations demonstrated that nanoparticles of silicon BC8 indeed generate multiple electron-hole pairs per photon even when exposed to visible light.

"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," stated co-author Gergely Zimanyi, professor of physics at UC Davis.

Other authors of the paper are Marton Voros and Adam Gali at the Budapest University of Technology and Economics, Hungary.

The work was funded by a National Science Foundation Solar Collaborative grant awarded to Zimanyi, Galli and colleagues at UC Davis and UC Santa Cruz in 2011.

2013-02-04