A funnel to capture solar energy!

Inverse charge funnelling in a two-dimensional semiconductor paves the way to highly efficient solar cells

The amount of energy received from the Sun by the surface of Earth in one hour, if converted into electricity, would power the whole world for one day. However, such energy conversion cannot be realised at present due to physical limitations in solar cells. Solar panels work by converting the energy of the light into electrical charges inside a material (typically a semiconductor such as Silicon), which are then extracted by metal electrodes into an external circuit, such as a battery or a mobile phone. Current technology for Silicon solar cells allows only 24% of the energy of the impinging light to be converted into electricity. This is due to fundamental limitations which impose a theoretical maximum efficiency of 34%, known as Shockley–Queisser limit.

At the University of Exeter we pioneered a novel technique which could overcome the aforementioned limits. The physical phenomenon, known as “charge-funnelling”, allows the efficient extraction of photo-generated charges into an external circuit using a non-uniform band-gap profile in a strain-engineered semiconductor. A simple analogy helps explain the concept. If we try to fill a bottle with a narrow neck (our battery) with a liquid (our energy) by simply pouring it from a bucket (the Sun) we will not get much in the bottle. Conversely, if we place a funnel on top of the bottle we obtain a much more efficient transfer of liquid. This is exactly what we do in our work, using a material called Hafnium Disulphide (chemical formula HfS2). The funnel is created by modifying the composition of the material using an intense laser light. Such modification induces strain in the material which, in turn, modifies the energy of the bands where the electrons move, creating the equivalent of a charge funnel.

Charge funnelling can enable so-called “hot-carrier” solar cells with a power conversion efficiency above 60%. This would allow to power entire cities with a fraction of the space (and cost) nowadays required with silicon-based solar panels. Furthermore, the  use of atomically-thin materials (materials which are between one and three atoms thick) will enable flexible and wearable solar cells, which could be embedded into fabric products such as clothing, parasols, umbrellas, etc.

Future research will focus on developing a scalable technique to engineer charge funnelling in large-scale devices. This comes with the challenge of materials production and fabrication compatibility with existent technology.

More about our discovery can be found this short video:

You can read the full paper in Nature Communications at the following link (open access): https://www.nature.com/articles/s41467-018-04099-7

2 Comments

  1. Daniel Krebs

    Hello Dr. De Sanctis,

    good news, to hear that solar cells finally started to the sky. 60% and more efficient, that means it could be possible to power an ev by its roof mounted cells alone. The german start up Sono Motors claims that their Sion today can make 30 km additional range on a sunny day provided by its traditionally solar cells inbuilt in the car structure, how many would it be using your fundamental breakthrough tec?
    Why not give it a try to do a solar powered trip around the world?
    Where is this guy in the states who did something near to this. He bought an old 1973 VW Bus and mounted a solar panel on the roof and golf car batteries underneath. He now can travel 40-50 miles/day with this vehicle, just charged by the sun. Is this the future or will reactive forces it hold back from mankind again, cause as J. P. Morgan stated to Nicola Tesla years before, there is no possibiltiy to mount a meter on it…
    So, Dr. De Sanctis, whish you all the best, hoping that your invention will accelerate the energy transition.

    Cheers,

    Daniel

    • Dear Daniel,
      thanks a lot for your comment. I like you suggestion, I will give it a try at least theoretically to see what the range could be. Our discovery is at proof-of-concept stage and lots of work is needed to bring it to the public. However I am optimistic that, as funding becomes available, we will be able to continue on this road to have a World powered by solar energy!

      Regards,

      Adolfo.

Leave a Reply

Your email address will not be published. Required fields are marked *