Most technologies for harnessing the sun’s energy capture the light itself, which is turned into electricity using photovoltaic materials. Others use the sun’s thermal energy, usually concentrating the sunlight with mirrors to generate enough heat to boil water and turn a generating turbine. A third, less common approach is to use the sun’s heat—also concentrated by mirrors—to generate electricity directly, using solid-state devices called thermophotovoltaics, which have their roots at MIT dating back to the 1950s.

Now, researchers at MIT have found a way to use thermophotovoltaic devices without mirrors to concentrate the sunlight, potentially making the system much simpler and less expensive. The key is to prevent the heat from escaping the thermoelectric material, something the MIT team achieved by using a photonic crystal, essentially an array of precisely spaced microscopic holes in a top layer of the material.

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