When you start to discuss the power conversion–efficiency of solar cells, you are bound to ruffle some feathers.
To many it’s an apples-and-oranges debate. You have multijunction solar cells with conversion efficiency rates at 42 percent while dye-sensitized solar cells are now reaching just 10 percent. It's hard to see how they compare—never mind compete.
But what are we really trying to get at with this standard? It would seem that we are trying to sort out the best alternative per kilowatt hour (kWh). Why we don’t set aside the whole energy conversion efficiency debate to focus on kWh figures remains a bit of a puzzle for me.
That said, researchers at the A*STAR Institute of Microelectronics in Singapore tackled the fact that the best thin-film photovoltaics only approach half the energy conversion efficiency of conventional bulk silicon solar cells.
The research, led by Navab Singh and published in the IEEE journal Electron Device Letters, brought about a thin film of silicon with “nanopillars” on the surface to heighten light absorption.
"By investigating a variety of appropriate vertical nanopillar designs, we can enhance the light-trapping and -collection efficiency of thin films to compensate for the efficiency loss caused by reduced material quality and quantity," says Singh.The trick, of course, is to match—or at least better approach—the energy conversion–efficiency rates of single-crystalline silicon solar cells with thin-film silicon solar cells. Whether this is the particular answer to achieving that remains to be seen, but it seems to be a move in the right direction, unlike the pursuit of ever-higher conversion rates.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.