University of Michigan (UM) researchers have invented colorful, see-through solar cells that may one day be used to make stained-glass windows, decorations and even shades that turn the sun’s energy into electricity.  The technology may also be a solution to photocell orientation to the sun problem.

Jay Guo, a professor of electrical engineering and computer science, mechanical engineering, and macromolecular science and engineering at UM. Guo is lead author of a paper about the work newly published online in Scientific Reports.

Guo said the cells, believed to be the first semi-transparent, colored photovoltaics, have the potential to vastly broaden the use of solar energy resources.  “I think this offers a very different way of utilizing solar technology rather than concentrating it in a small area. Today, solar panels are black and the only place you can put them on a building is the rooftop. And the rooftop of a typical high-rise is so tiny,” he said.

“We think we can make solar panels more beautiful – any color a designer wants. And we can vastly deploy these panels, even indoors.”

Suddenly, absent the garish black look, photovoltaic technology has some redeeming value – and may very well offer some aesthetic and intrinsic value beyond the energy production segment in their cost.  This could dramatically change the cnosumer investment proposition.

Guo envisions them on the sides of buildings, as energy-harvesting billboards, window shades, and as a thin layer on homes and cities. Such an approach, he says, could be especially attractive in densely populated cities.

Transparent Color Solar Cells.  Image Credit: Joseph Xu, Michigan Engineering Communications & Marketing.  Click image for the largest view.

Transparent Color Solar Cells.
Image Credit: Joseph Xu, Michigan Engineering Communications & Marketing. Click image for the largest view.

In a palm-sized American flag slide, the team demonstrated the technology.

“All the red stripes, the blue background and so on, they are all working solar cells,” Guo said.

The Stars and Stripes example achieves a 2 percent efficiency.  A meter-square panel could generate enough electricity to power fluorescent light bulbs and small electronic gadgets, Guo said.  State-of-the art organic cells in research labs are roughly 10 percent efficient.

The UM researchers are working to improve the efficiency numbers with new materials, but there will always be a tradeoff between beauty and utility in this case.  Traditional black solar cells absorb all wavelengths of visible light. Guo’s cells are designed to transmit, or – in other versions – reflect certain colors, so by nature they’re reflecting energy from those wavelengths back out to our eyes rather than converting it to electricity.

Unlike other color solar cells, Guo’s don’t rely on dyes or microstructures that can blur the image behind them.  The cells are mechanically structured to transmit certain light wavelengths.  To get different colors, they varied the thickness of the semiconductor layer of amorphous silicon in the cells.  The blue regions are six nanometers thick while the red is 31 (the team also made green, but that color isn’t in the flag).

Amorphous silicon is commonly used in screens on cell phones, laptops and large LCD screens, in addition to solar cells.  They sandwiched an ultrathin sheet of it between two semi-transparent electrodes that could let light in and also carry away the electrical current.

One of the charge transport layers is made of an organic material.  The combination of both organic and inorganic components makes a hybrid structure, letting the researchers make cells that are 10 times thinner than traditional amorphous silicon solar cells.  The organic layer replaces a thick ‘doped’ circuit layer that would control the flow of electricity.

The ultrathin, hybrid design helps the cells hold their color and leads to a nearly 100 percent quantum efficiency.  Quantum efficiency is different from overall efficiency.  It refers to the percentage of light particles the device catches that lead to electrical current in that charge transport layer.  Solar cells can leak current after this point, but researchers strive for a high number.

The cells’ hues don’t change based on viewing angle, which is important for several reasons.  It means manufacturers could lock in color for precise pictures or patterns.  It’s also a sign that the devices are soaking up the same amount of light regardless of where the sun is in the sky.  Conventional solar panels pivot across the day to track rays.

“Solar energy is essentially inexhaustible, and it’s the only energy source that can sustain us long-term,” Guo said. “We have to figure out how to use as much of it as we can.”

Wait!  Back up a moment, “a sign that the devices are soaking up the same amount of light regardless of where the sun is in the sky.”

This team has much more at hand than colors.


1 Comment so far

  1. DIVING LIGHT on July 8, 2014 3:14 PM

    Beauty May Come to Solar Cells | New Energy and Fuel

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