McCormick researchers have designed a geometrically-patterned light scattering layer that could make solar cells more efficient and less expensive.

McCormick researchers have designed a geometrically-patterned light scattering layer that could make solar cells more efficient and less expensive.

From Northwestern University:

In a potentially breakthrough discovery, researchers at Northwestern University have designed a new type of organic solar cell that will very likely lead to much higher efficiency and cheaper solar power.

The new cell design is based around a new geometrical pattern to be used in the ‘scattering layer’ of a solar cell, which works to keep the light trapped in the cell for longer.

The specific geometrical pattern was obtained by using a mathematical search algorithm modeled on natural evolution to identify the optimal design “for capturing and holding light in thin-cell organic solar cells.”

“The resulting design exhibited a three-fold increase over the Yablonovitch Limit, a thermodynamic limit developed in the 1980s that statistically describes how long a photon can be trapped in a semiconductor.”

According to the researchers, the new design will greatly increase the efficiency of organic solar cells.

It’s currently planned for solar cells, with the pattern in question to be fabricated with partners at Argonne National Laboratory.

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From Princeton University:

Princeton researchers have found a simple and economical way to nearly triple the efficiency of organic solar cells, the cheap and flexible plastic devices that many scientists believe could be the future of solar power.

The researchers, led by electrical engineer Stephen Chou, were able to increase the efficiency of the solar cells 175 percent by using a nanostructured “sandwich” of metal and plastic that collects and traps light.

Chou, the Joseph C. Elgin Professor of Engineering, said the research team used nanotechnology to overcome two primary challenges that cause solar cells to lose energy: light reflecting from the cell, and the inability to fully capture light that enters the cell.

organic-solar-triple-efficiency1With their new metallic sandwich, the researchers were able to address both problems. The sandwich — called a subwavelength plasmonic cavity — has an extraordinary ability to dampen reflection and trap light. The new technique allowed Chou’s team to create a solar cell that only reflects about 4 percent of light and absorbs as much as 96 percent. It demonstrates 52 percent higher efficiency in converting light to electrical energy than a conventional solar cell.

That is for direct sunlight. The structure achieves even more efficiency for light that strikes the solar cell at large angles, which occurs on cloudy days or when the cell is not directly facing the sun. By capturing these angled rays, the new structure boosts efficiency by an additional 81 percent, leading to the 175 percent total increase.

The physics behinorganic-solar-triple-efficiency2d the innovation is formidably complex. But the device structure, in concept, is fairly simple.

The top layer, known as the window layer, of the new solar cell uses an incredibly fine metal mesh: the metal is 30 nanometers thick, and each hole is 175 nanometers in diameter and 25 nanometers apart. (A nanometer is a billionth of a meter and about one hundred-thousandth the width of human hair). This mesh replaces the conventional window layer typically made of a material called indium-tin-oxide (ITO)

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