Claiming that a solar cell can produce energy even in the dark sounds a little like the beginning of a joke, but I assure you it is not so. A team of scientists from the Australian National University (ANU) and the University of California Berkeley (UC Berkeley) have successfully made a prototype of a device, which can become a part of super-efficient thermophotovoltaic cells. Such a cell could generate electricity even if it is not placed in direct sunlight. This cell would absorb infrared radiation and convert it into an electric current, and this can happen even in the dark.
The basis for this device is a new optical magnetic metamaterial, which they created by alternatingly stacking twenty nanomaterial sheets of gold and magnesium fluoride (30 nm and 45 nm thick, respectively), and setting them on a 50-nm-thin silicon nitride base. Next they produced cavities in the material by cutting a series of elongated holes in it via focused ion milling.
This process allows the material to exploit a phenomenon known as “magnetic hyperbolic dispersion.” This means that the dispersion characteristics of this new material take on a hyperbolic form, which results in a directional, coherent and polarized thermal emission, such as infrared radiation. As a result of creating the cavities in the surface of the material, the magnetic hyperbolic dispersion can also be tuned to specific frequencies and intensities. This means that, when paired as an emitter with a thermophotovoltaic cell, the material will greatly increase the thermal transfer efficiencies of it.
The researchers are sure that this new device could also be paired with a heater to create on-demand power, or even added to car and other engines, to turn radiated heat into electricity. They also believe that making thermovoltaic cells from this new material could considerably improve their radiative heat transfer capability.