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Karate on electrons to give a bigger zap from light

How to double the power from light, by breaking electron pairs in half.

I work on the development of highly efficient silicon solar cells. To achieve this, I combine classical solar materials, with a peculiar family of organic materials which are capable of making better use of blue photons. The process which enables this is called “Singlet Fission”.

To get our heads around this process, we should understand a bit of the background: The sun emits more red photons than blue ones, however blue photons are more energetic. The key to design a good solar cell is to absorb both blue and red photons with minimal losses. Unfortunately no material is good at absorbing both the blue and the red, hereby we need to select materials which absorb each component individually and then put them together. I work of finding different ways to combine silicon, which is good at absorbing the red, with these singlet fission materials which not only are good at absorbing the blue, but are also capable of breaking high energy electrons into two low energy electrons, multiplying the current.

When a blue photon is normally absorbed, it excites an electron to a highly energetic state. However when we transfer this high-energy electron into silicon a lot of energy is transformed into heat and lost.

For this reason we need this special family of small molecules which undergo “Singlet Fission”. When a high-energy electron is generated in one of these materials, the singlet fission mechanism activates and breaks the high-energy electron pair into two low-energy electrons pairs, multiplying the number of electrons produced. Since the energy of each electron has been halved, they transfer into silicon without energy losses.

At the moment the cost of producing a solar panel is not limited by the cost of the “active material”, the material that generates the electrons, but is instead limited by the cost of manufacturing, supplying and setting up the solar panel itself. The meaning of this for those who are working on the development of solar cells is that there is no need on trying to make solar cells out of cheap active materials anymore. The crucial objective now is to push the efficiency forward and singlet fission has a huge potential to break current efficiency limits.

Luis Pazos

Cover image credit: Chao-Yang Lu

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