A rainbow is a common and appreciated sight, as it indicates better weather with chances of sunshine. This is because a rainbow is seen when light from the Sun is dispersed by water droplets in the rain. We can observe red, yellow, green and blue light. The energy of a light particle (photon) is related to the colour that we perceive, for example blue light is higher in energy than green light, which in turn is higher in energy than red light. Even higher in energy than blue is ultra violet (UV) light, which explains why we must protect ourselves from prolonged exposure to the Sun’s UV light with sunscreen.

In our aim towards developing more efficient solar cells and other solar harvesting applications it is crucial to optimize which colours are absorbed by the device material. Only colours of light with sufficient energy can be used in a solar cell or other solar driven device. Photons with too low energy (of wrong colour) are not absorbed by the device and are therefore wasted. On the otherhand, photons that have too much energy, like blue light, looses most of its energy as heat in a device. My research focuses on developing and understanding materials that can combine or split photons, so that the light reaching the solar harvesting device is optimised.

Figure showing a solar cell with a singlet fission material that can convert high energy photons to multiple low energy photons

Singlet Fission
Singlet fission is a process in some organic molecules that splits a singlet excited state into two triplet excited states on neighbouring molecules. In this way the photon energy can be split in two. My research in this fascinating area has focused on how to make the triplet states useful in solar cells, by turning them back into photons.
See some of these publications for more details:
ACS Nano 2020, 14, 4, 4224–4234.
J. Phys. Chem. Lett. 2020, 11, 17, 7239–7244.

Photon Upconversion
The process where two low energy photons are combined to generate one photon of higher energy is called photon upconversion. Photon upconversion can be achieve through a process known as triplet-triplet annihilation (TTA), which is the reverse of singlet fission. Here two triplet excited states are fused to form one high energy singlet state. I have focused on developing materials to achieve photon upconversion in the solid state, as well as to understand the limits of the TTA process better.
See some of these publications for more details:
Phys. Chem. Chem. Phys., 2017, 19, 10931-10939.
Chem. Sci., 2017,8, 5488-5496.
J. Am. Chem. Soc. 2019, 141, 24, 9578–9584.
Coord. Chem. Rev., 2018, 362, 54-71.