What are excitonic solar cells?
Excitonic solar cells are devices that produce electricity from the sun’s energy through the creation of an “exciton,” which is an electron-hole pair.
How do they work?
When a photon (a particle of light) hits the light-active component in an excitonic solar cell a negatively charged electron is excited to higher energy. A positively charged “hole” is therefore also created on the molecule at the point where the electron is now absent. When the electron is initially excited it remains strongly bound to the hole since they have opposite charges and are both confined to the same small molecule. This electron-hole pairing is what we call an exciton which gives these type of solar cells their name. An interface between two different materials – an “electron-transfer material” that accepts the electrons and a “hole-transport material” that accepts the holes – is then needed to split the exciton into a separate electron and a hole. The electron and the hole can then separately migrate to different electrodes.
The charge separation of the negative charge and positive charges to different electrodes is crucial as it sets up an electrical potential (voltage). This drives a flow of electrons (current) round an outer circuit (that connects the two electrodes) where they can do some work, like power an electrical device. Once the electrons recombine with the hole at the other electrode, the system is reset and the whole process can be started again with another photon.
How are they different from conventional solar cells?
In conventional solar cells, such as those made of silicon, a negatively charged electron and positively charged hole are also created when sunlight hits the cell. However the excited electron and corresponding hole can immediately separate and easily travel away from each other. In excitonic solar cells, the electron and whole are tightly bound together. This means that they cannot travel far without recombining with each other.
What types are there?
There are several different types of excitonic solar cells and in each, the light-active component and other cell materials are different. Currently the two main areas of research
Dye-sensitised solar cells (DSSCs), and
Organic and hybrid photovoltaics (OPVs and hPVs). Find more about both of these technologies by clicking the buttons below.