Record-smashing solar cell raises commercialization hopes

Source: Christa Marshall, E&E reporter • Posted: Monday, May 23, 2016

There’s a new world record for solar cell efficiency.

Engineers at the University of New South Wales in Australia announced this week that they had turned 34.5 percent of unconcentrated sunlight into electricity, blowing away the old world record by 44 percent.

Previously, scientists had achieved an electric conversion rate of more than 40 percent, but only by using mirrors that concentrate light. There’s never been such a high electricity conversion rate tapping regular sunlight without concentrators, according to the university.

The researchers behind the project say the results are significant partly because a 35 percent efficiency level was considered unattainable for years. Efficiency of solar technologies in general is considered a key factor in bringing more solar online cheaply (E&ENews PM, May 18). The National Renewable Energy Laboratory confirmed the 34.5 percent result.

“We’re not going to have to wait until 2050” for a commercial product, Martin Green, director at the University of New South Wales’ Australian Centre for Advanced Photovoltaics, who worked on the project, said during an online news conference.

The device that achieved the results consists of a 28-square-centimeter module embedded in a triangular glass prism. The prism has a silicon cell on one face and a multilayered solar cell known as a “triple-junction” cell on the other.

The technology splits sunlight into four colored bands, then directs each band to the part of the unit that best converts it into electricity, said Mark Keevers, a senior research fellow at the center, in an email. For example, one of the layers in the triple-junction cell contains germanium, which targets the longest wavelengths of light. Other layers in the triple-junction cell target shorter wavelengths.

A filter then “reflects just a narrow band of infrared light back up, which is then trapped in the glass prism and makes its way to the silicon cell,” Keevers said.

The next phase of the project is to scale up the module. The previous world record, from California-based Alta Devices, occurred on a much larger surface of 800 square centimeters. Keevers said the team plans to assemble about 30 of the modules into a large 900-square-centimeter unit.

The optimal use for the technology currently is in solar towers that use mirrors to concentrate sunlight, the researchers said.

It’s not ready for widespread rooftop solar use yet and may not be for at least a decade, said Keevers. That could occur eventually, but there needs to be a cheaper way to manufacture the device, he said. He and Green said they are examining techniques to lower manufacturing costs.

One idea is to generate “synthetic silicon” material that uses a combination of copper and other substances, according to Keevers. In theory, it could respond better to some bands of light than silicon, but also mimic its electrical properties.

As is the case with many technologies, there are obstacles to scaling up, including the potential for more energy losses when a larger unit is connected to the grid.

“It is a proof of concept at the prototype level. Its ability to compete with conventional modules in the marketplace has not been demonstrated. Its durability has not been demonstrated,” said Keith Emery, a principal engineer at the National Renewable Energy Laboratory.

Financing is a challenge, too. The research team may lose funding from the Australian Renewable Energy Agency because of agency restructuring, which could be “disastrous” for advancing the project, Green said.