UC Berkeley research group rethinks solar cell design

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If different materials, textures and shapes are used in solar cells, the technology could produce more efficient electricity, a campus research group has found.

Research conducted by Eli Yablonovitch, a campus professor of electrical engineering and computer science, and graduate student Owen Miller showed that reimagining the construction of solar cells could increase the percentage of absorbed light that is converted into electricity.

“The world of solar cells needs more efficiency,” Yablonovitch said. “One of the reasons why there are problems today is because they are based on a technology that is not capable of (its) full potential.”

To produce electricity, solar cells require sufficient current and voltage. In the past, researchers have focused on maximizing the electrical current flowing inside of the solar cell, rather than maximizing the number of photons emitted when light hits the surface of the cell.

Because photons released into the atmosphere take energy with them, Miller said it was previously understood that greater photon emission meant less energy efficiency. But in the process of his research, Miller, along with Yablonovitch, realized that solar cells which emitted more photons without losing thermal energy made for a more efficient cell.

Based on this research, scientists at Alta Devices — a start-up company founded by Yablonovitch — used the semiconductor gallium arsenide to create solar cells that converted absorbed light into more electricity while minimizing heat loss than cells made with typical materials, including silicon.

Today, most solar cells are made of one material, which scientists have realized can convert a maximum of 33.5 percent of the absorbed solar energy. From 1990 to 2010, the efficiency of solar cells only increased 1.3 percent, from converting 25.1 percent of absorbed light to 26.4 percent.

But, in the past two years, the prototype produced by Alta Devices reached an efficiency of 28.3 percent, shattering prior records by about 2 percent, Miller said.

“There’s a lot of benefit to be reaped,” he said. “If you’re doing solar cell production, you need to use this technology.”

Miller added that this research allows for the use of materials other than silicon — which, given its capacity to reliably conduct electricity, is what many solar cells are made of today — to create solar cells.

But even the efficiency record currently held by this material could be broken by using a combination of materials, textures and structural designs to build solar cells, according to Miller.

“I think the theory has been done and now it’s up to the experimentation and fabrication side to improve the efficiency,” Miller said.

Solar cells are generally stacked on top of one another on flat panels, but Miller said that laying the cells side-by-side or positioned in a serpentine shape could convert more sunlight into electricity.

Changing the positioning of solar cells requires constant monitoring of the light exposure to each cell and the angle at which sunlight hits the cells — structural designs that remain costly to manufacture, Miller said.

As energy-efficient technologies continue to attract funding from government and private research agencies, Miller said he hopes that by 2016, solar cell technology will reach cost parity with other fuels and be used in many homes across the country.

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  • Calipenguin

    Great job Eli and Owen!  Keep this technology to the USA and don’t give it away to China.  Don’t set up a manufacturing partnership with a Chinese company which would simply steal this technology.  GaAs is not as cost effective as Si yet so the additional efficiency may not make GaAs  competitive with the cutthroat pricing of Chinese Si panels, but you guys will succeed some day.  Ask for funding not only from the DOE but also the US Armed Forces, which is very interested in efficient solar panels.

  • anon

    Good at ‘rethinking’, not good at thinking?