Researchers want to double solar cell efficiency via quantum mechanics

American scientists have developed a prototype of a minuscule photovoltaic cell that is able to significantly improve the efficiency of solar cells via a quantum mechanical process. It turned out to be possible to make one photon generate two electrons.

The photovoltaic cell the scientists created consists of two atomic layers of the inorganic compound tungsten diselenide (WSe2) and a layer of molybdenum diselenide (MoSe2). In this experimental photovoltaic cell, the researchers saw that when a photon hits the layers of tungsten diselenide, an electron is released that can move freely through the conductive material. This also happens with normal photovoltaic cells, but the material from Riverside University showed interesting properties.

At the point where the two materials are in contact, the electron transitions into the molybdenum diselenide. In that second layer, the electron takes on a lower energy state, where the extra energy released during the transition turned out to be able to generate a second electron in the tungsten diselenide. By applying a weak electric field with a voltage of 1.2V, the electron moves towards the molybdenum diselenide. The energy state of electrons in that material is lower than in the tungsten diselenide, so the electron can lose energy, enough to release a second electron in the tungsten diselenide.

This would work because atomic monolayers of the two compounds are used, causing quantum mechanical effects. The electrons that are released behave like waves, with the thicknesses of the materials approaching the wavelength of the electrons. This traps the electrons, but exactly how this leads to sufficient energy to release a second electron is unclear. However, even more electrons might be released when the temperature is increased: the researchers conducted their experiments at 340K, about 70 degrees Celsius.

In regular solar cells, a photon usually generates only one electron. Doubling this would mean that twice as much electricity could be generated. Because the materials used are only the thickness of an atom, are virtually transparent and flexible, the researchers say they can eventually be integrated into paint, solar cells or even textiles, for example.

The research is published in the scientific journal Nature Nanotechnology, under the title Hot carrier-enhanced interlayer electron–hole pair multiplication in 2D semiconductor heterostructure photocells.