Ultrathin and Ultraflexible Organic Solar Cell: Energy From the Sun

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Ready for better solar cells? A new type of innovative organic solar cells have recently been developed, according to a study published this month in Nature Communications. These new solar cells are very light, very thin, and so flexible that they can be wrapped around a human hair – this type of organic solar cell could potentially be used for devices in textiles, and remote sensing systems.

What Are Organic Solar Cells?

Electron delocalization in benzene: Image by Clara Piccirillo

Solar cells, also called photovoltaics (PVs), are devices employed to covert the energy from the sun into electricity. Many solar cells are based on semiconductor materials; the electricity is generated with the absorbtion of light by the bandgap of the semiconductor used. There is, however, another class of PVs, which employs organic molecules to convert light into electricity. They are referred to as Organic PhotoVoltaic (OPV) cells.

Electron Delocalization

The main characteristic of the organic molecules used in OPVs is that of electron delocalization. This means that the electrons which form the chemical bonds are not localized with a particular atom; on the contrary, they are free to move within the molecule. The picture to the left shows an example of electron delocalization for benzene; electrons are represented like a “cloud,” delocalised between all carbon atoms. Although this molecule is not used for OPVs, the principle of the electron distribution all over the molecule is the same. Molecules with this electronic structure may have a bandgap; the mechanism to generate electricity is, therefore, similar to that described for semiconductors.

How OPVs Are Made

OPVs can be made with either one or two conductive organic materials. When two materials are used, the materials employed have to have certain characteristics, so that there can be a charge transfer from one material to the other. The two materials could be arranged in the form of two separate layers, one on top of the other; in other cases, the materials could be mixed together, to get a more effective charge transfer.

In all cases, the active material(s) is(are) placed between two electrodes, for the transport of the generated charges, and all of these parts together are placed on an appropriate substrate.

OPV Performances

The main drawback of OPVs is that their efficiency is normally lower compared to the inorganic photovoltaic cells (between 4 and 8 %). However, they have other advantages, such as:

  • OPVs are normally lighter and more flexible than PVs – this means that they can be used for several practical applications, such as textiles and remote sensing systems.
  • Moreover, the fabrication technique for OPVs is compatible with a reel-to-reel process, suitable for large scale production, which lowers production costs.

Many of these properties are due to the fact that, instead of the conductive glass normally used, thin plastic materials can be used as a substrate in the manufacture of OPVs.

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