They are testing a method to extract two electrons from each incident photon. Objectives of photovoltaic research move the theoretical limit of silicon solar cells to 35%.

For each photovoltaic material, there is a theoretical maximum efficiency value, that is, a limit to the amount of solar energy that can be converted into electricity.

For silicon solar cells, this value is equivalent to 29.1% of the incident light but, being the most widely used product on the market, the industry has been trying for years technical strategies to increase this percentage.

One of them refers to the photon-electron relationship. In traditional cellular semiconductors, each incident photon gives all of its energy to an electron, which frees itself from chemical bonds and begins to move inside the material. A one-to-one relationship that remains unchanged even if this photon has transported twice the energy necessary to release an electron.

A method is being studied to obtain the extraction of two electrons per photon (instead of one), thus opening the door to the solar cells capable of exceeding their theoretical efficiency limits.

After years of commitment, MIT is convinced it has found the right path. In today’s article published in Nature, a group of scientists from MIT and colleagues at Princeton University discuss how they’ve been successful in improving silicon solar cells.

The solution lies in a well-known class of materials which have “excited states” called excitons. That is, the scientists explain, “packets of energy that propagate as electrons in a circuitBut with properties very different from those of electrons. “You can use them to change the energy, you can cut them in half, you can combine them. “

The group’s work was to integrate this capacity into silicon, a material that has no excitons. The turning point came from the connection of silicon with an organic crystal, tetracene, through a thin intermediate layer of hafnium oxynitride. Tetracene is a material capable of making this type of energy work by multiplying: when exposed to light, it first absorbs a photon, forming an exciton that undergoes rapid fission into two excited states (a physical phenomenon known as single fission or single fission), each with half the energy of the original state.

The hafnium oxynitride layer acted as a bridge for excited states down to silicon. The mechanism produces a double the amount of energy and scientists are convinced that in this way the theoretical limit can be shifted up to a maximum of 35%.

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