Solar panels are cheaper than ever these days, but installation costs can still be considerable for homeowners. More efficient solar panels can recapture the cost of their installation more quickly, so making panels that are better at converting sunlight into electricity is a key focus of solar research and development.

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The silicon-based cells that make up a solar panel have a theoretical efficiency limit of 29 percent, but so far that number has proven elusive.

Practical efficiency rates in the low-20-percent range have been considered very good for commercial solar panels. But researchers with Japanese chemical manufacturer Kaneka Corporation have built a solar cell with a photo conversion …