Oxygen, from enemy to new ally of solar cells
UNSW Sydney / Exciton Science

A group of researchers have succeeded in “converting” low-energy photons, normally rejected by silicon, into new light suitable for solar cells.

In recent years, solar cell research has made great strides. It has increased efficiency and stability, reduced production costs and introduced new innovative materials.

However, one of the goals of the sector is to create photovoltaic technology that captures all light energy and transforms it into electricity.

The sun has a wide electromagnetic spectrum: a rainbow of colors, each of which corresponds to “a photon of different energy”. In theory, they are all usable, but semiconductors in solar cells have very precise limits on the wavelength they can absorb. And even in the best tandem technologies, only two-thirds of the available photons can be collected.

Solar energy is not just visible light. The spectrum is wide including infrared light which provides heat and ultraviolet light which can burn our skin. Most solar cells are made of silicon, which is not able to respond to infrared light.

Tim Schmidt, University of New South Wales.

To resolve this limitation, Schmidt and his colleagues turned to upscaling. It is a process of photochemical conversion which makes it possible to absorb two photons, normally not sufficiently energetic and therefore “wasted” by the semiconductor used, to have the emission of a single but more powerful photon.

One way to do this is to capture more low energy photons and stick them together.

Tim schmidt

The best part is that often without oxygen, a lot of things work well. And as soon as you let it in, they stop working. It has been a real Achilles heel for a long time, but now we have not only found a way to overcome the problem, but the oxygen is helping us as well.

Jared Cole, RMIT University.

Efficacy remains low, but scientists are considering strategies to improve the technique in the near future.

The research was published in Photonics of nature.

More information: unsw.edu.au