Semiconductor breakthrough may be game-changer for organic solar cells

 

  • Mostly inorganic solar cells are widely used rather organics can be made of inexpensive, flexible carbon based materials like plastic. Organic has poor conductivity.
  • A thin layer of fullerene molecules the curious round carbon molecules also called Buckyballs can enable electrons to travel up to several centimeters from the point where they’re knocked loose by a photon. That’s a dramatic increase; in today’s organic cells, electrons can travel only a few hundred nanometers or less.
  • Electrons, moving from one atom to another, make up the electric current in a solar cell or electronic component.
  • Materials like silicon, used in today’s inorganic solar cells and other semiconductors, have tightly bound atomic networks that make it easy for electrons to travel through the material.
  • But organic materials have much looser bonds between individual molecules, which can trap electrons.
  • The ability to make electrons move more freely in organic semiconductors could have far-reaching implications.
  • For example, the surface of today’s organic solar cells must be covered with a conductive electrode that collects electrons at the point where they’re initially generated.
  • But freely moving electrons can be collected far away from their point of origination. This could enable manufacturers to shrink the conductive electrode into an invisible grid, paving the way for transparent cells that could be used on windows and other surfaces.
  • The initial discovery of the phenomenon came as something of an accident as the team was experimenting with organic solar cell architecture in hopes of boosting efficiency.
  • Using a common technique called vacuum thermal evaporation, they layered in a thin film of C60 fullerenes each made of 60 carbon atoms on top of an organic cell’s power-producing layer, where the photons from sunlight knock electrons loose from their associated molecules.
  • On top of the fullerenes, they put another layer to prevent the electrons from escaping. The researchers discovered something they’d never seen before in an organic electrons were skittering unfettered through the material, even outside the power-generating area of the cell.
  • Through months of experimentation, they determined that the fullerene layer formed what’s known as an energy well a low-energy area that prevents the negatively charged electrons from recombining with the positive charges left behind in the power-producing layer.
  • So they continue to move freely in the fullerene layer instead of recombining in the power-producing layer, as they normally would. It’s like a massive antenna that can collect an electron charge from anywhere in the device.

 

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