Scientists at the U.S. Department of Energy’s Idaho National Laboratory have announced that they are harnessing energy with a solar cell that will work even in the dark.

The key is their ability to harvest infrared radiation as well as visible light, Almost half of the available energy in the spectrum of solar radiation is in the infrared band – and infrared is re-emitted as heat by the Earth’s surface after the sun has gone down. A large amount of infrared radiation is also produced by industrial processes.

The new devices consist of nano-antennas which can absorb radiation at many angles. Laboratory tests have shown them to have an overall efficiency of 46% under ideal conditions. Conventional solar cells are about 25% efficient under optimal light conditions.

Unlike photovoltaic cells, which use photons to liberate electrons, the nano-antennas resonate when hit by light waves and that generates an alternating current that can be harnessed.

The researchers envision multiple layers of antennas, with each layer tuned to a different optical frequency, that could capture both visible and infrared radiation. They believe that ssuch arrays could have an efficiency as high as 84%.

One of the main remaining challenges for the technology is that existing silicon diodes do not operate fast enough to convert the very rapid alternating current produced using the nano-antennas into direct current. However, a research team at the University of Colorado, have independently taken a significant step in tackling this problem by creating novel diodes capable of handling high optical frequencies. Both groups expect to combine the diodes and antennas into working prototypes within months.