November 24, 2008
Reflective Coating Boost Photovoltaic Efficiency

Reflective coatings combined with very thin silicon films yield high efficiency with potential for substantial cost reduction.

CAMBRIDGE, Mass. New ways of squeezing out greater efficiency from solar photovoltaic cells are emerging from computer simulations and lab tests conducted by a team of physicists and engineers at MIT.

Using computer modeling and a variety of advanced chip-manufacturing techniques, they have applied an antireflection coating to the front, and a novel combination of multi-layered reflective coatings and a tightly spaced array of lines called a diffraction grating to the backs of ultrathin silicon films to boost the cells' output by as much as 50 percent.

The carefully designed layers deposited on the back of the cell cause the light to bounce around longer inside the thin silicon layer, giving it time to deposit its energy and produce an electric current. Without these coatings, light would just be reflected back out into the surrounding air, said Peter Bermel, a postdoctoral researcher in MIT's physics department who has been working on the project.

But what was the absolute efficiency of conversion? Is the 50% an increase over ultrathin silicon film PV efficiency and not over conventional thicker silicon PV?

The thinnest of this design cuts the cost of expensive silicon crystal.

And the potential for savings is great, because the high-quality silicon crystal substrates used in conventional solar cells represent about half the cost, and the thin films in this version use only about 1 percent as much silicon, Bermel said.

This project, along with other research work going on now in solar cells, has the potential to get costs down "so that it becomes competitive with grid electricity," Bermel said. While no single project is likely to achieve that goal, he said, this work is "the kind of science that needs to be explored in order to achieve that."

I am increasingly optimistic that the cost of PV is going to plummet. Now if only technological advances for lightweight batteries suitable for cars could cause similar cost reductions for electric cars we'd gain a major piece of the puzzle needed for migration away from fossil fuels.

Share |      Randall Parker, 2008 November 24 10:23 PM  Energy Solar

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