Thermophotovoltaic Solar Cells Produce Electricity in the Dark

Scientists developed a new nanomaterial that can make solar cells generate electricity in the dark.

“Solar power generation in the dark? How is this possible?” If these were the questions that popped up in your mind when you read the title, I would say, you have every right to ask. This is especially the case since most commonly solar cells are associated with light. But solar radiation is also heat, something that is not taken into account in solar power generation. Or at least not yet.

A team of physicists from Australian National University (ANU) and the University of California Berkeley (UC Berkeley) looked for ways to use the thermal property of solar radiation, and see if they can incorporate it in solar cells. The aim of the exercise was to make solar cells produce electricity in the dark.

Their attempt resulted in the development of a revolutionary material, which is made of 20 thin gold and magnesium fluoride nanosheets. The two types of layers are stacked, alternating each other, and placed on a thin silicon nitride base. This material is then cut to form cavities, or long holes, with focused ion milling.

The new material is an optical magnetic metamaterial, which can be added to solar cells and turn them into thermophotovoltaic cells. In other words, they can generate electricity from both light and heat. They can harness the direct sunlight, but they can also absorb the infrared radiation and turn it into an electrical current. This latter function is what makes them unique, or to be more precise, enables them to generate power in the dark.

This was possible due to the so-called “magnetic hyperbolic dispersion” process. This essentially is the process that makes light disperse in a very intense pattern, due to the strong interaction of the magnetic component of light with the material. As a result, the material is much brighter and it gets heated by the infrared radiation.

At a nanoscale, inside the new material, this magnetic hyperbolic dispersion can be set to specific frequencies and intensity. When used as an emitter in a combination withthermophotovoltaic cells, this increases the efficiency of the thermal transfer.

According to the scientists behind the experiment, these new thermophotovoltaic cells can be much more efficient than regular solar cells. Thanks to the new material can give light to a new line of products- solar cells that work in the dark, producing energy when the sun is not shining.

The authors see many potential applications of their new discovery, including on-demand power generation and recycling of radiative heat from car engines.

More details can be found in the article, published in Nature Communications.

Image: Dr Kruk next to a diagram of the metamaterial structure. Image Stuart Hay, ANU