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Using plastic to absorb light could lower the cost of solar power.

By Kevin Bullis

A thin sheet of dyed plastic could cut the cost of solar power, particularly for applications that require solar cells to be highly efficient and flexible.

Researchers at the University of Illinois at Urbana-Champaign are using the plastic to gather sunlight and concentrate it onto a solar cell made of gallium arsenide in an experimental setup. Doing so doubled the power output of the cells.

So far, the researchers have shown that the approach works with a single solar cell, but they plan to make larger sheets of plastic dotted with arrays of many tiny solar cells. The approach could either let a smaller solar panel produce more electricity, or make a panel cheaper by reducing the amount of photovoltaic material needed.

“It’s lower cost compared to what you would have to do to get the same efficiency by completely coating the surface with active solar material,” saysJohn Rogers, professor of materials science and engineering and chemistry at the University of Illinois. The work was presented at the Materials Research Society conference in Boston this week.

As light hits the plastic sheet, a specially selected dye absorbs it. The dye is luminescent—meaning that after it absorbs light, it reëmits it. But the light it emits is largely confined inside the plastic sheet. So it bounces along inside the plastic until it reaches a solar cell, much in the same way light is guided along inside a fiber optic cable. The dye absorbs only part of the solar spectrum. So to further boost power output, the researchers added a reflective material that directs some of the light that the dye doesn’t absorb to the solar cell.

The approach could be compatible with another innovation from the same group of researchers—a technique for making flexible and stretchable solar cells that can conform to irregular surfaces (see “Making Stretchable Electronics”).

Flexible solar panels could find new uses. The military, for example, is interested in laminating solar cells to soldiers’ helmets to power their electronic gear. Bendable cells could also conform to the wings and fuselage of small drones to charge on-board batteries and extend their flight times. And the technology might even be used for cases that recharge tablets and other portable electronics.

There are other ways to concentrate sunlight and direct and reduce the amount of solar cell material needed. Rogers’s group has founded a company, Semprius, that can concentrate sunlight 1,600 times, compared to just 10 times for the dyed plastic sheet (see “Ultra-Efficient Solar”). But the concentrators used to do this are bulky and require a tracking system to keep them pointed at the sun as it moves through the sky. Such systems might lead to low-cost solar power for the grid, but they’re impractical for solar helmets or tablets. In contrast, the dye-coated plastic is thin and lightweight and can absorb light coming from different angles, making tracking unnecessary.