The scientific technique of singlet fission was first observed in glowing crystals nearly half a century ago, but now scientists are looking at it once again as a way to improve the efficiency of modern solar cells.
The process allows a single photon of light to release two electrons instead of the usual one, and a new paper published in the Journal of Physical Chemistry Letters claims this could increase the rate of energy conversion in solar panels by as much as 30%.
Solar panels currently work by absorbing a photon of light and then creating a exciton, which splits into two electrons and is then harnessed in the panel as electricity. However, in singlet fission a highly charged photon can emit two excitons, and therefore four electrons, creating the possibility of a solar cell with a 40% efficiency.
In the early 60s and 70s, singlet fission was first described in order to explain the strange glow coming from various fluorescent organic crystals. However, the process was forgotten soon after.
When the current study’s first author Christopher Bardeen and some fellow scientists were working on ways to increase the output of solar panels in 2006, the concept of singlet fission came up once more.
The group then went on to not only prove that the process is real but also that it could be used with many different materials.
The next step in the process is to involve these materials in the design of solar panels in order to increase their efficiency. It is hoped that by using the singlet fission process, their energy conversion efficiency can be increased from the current 20-25% to beyond the Shockley-Queisser Limit of 32%.
The Shockley-Queisser Limit has been exceeded in the past. Previously, intelligent engineering processes allowed a conversion efficiency of up to 50% by combining semiconductor panels together. Unfortunately this technique is very costly and therefore restricted mostly to military and space programs. Many scientists believe that singlet fission, and other similar techniques, are now the only cost-effective way of increasing the efficiency of solar panels.
Scientific understanding of singlet fission is still in the early stages however, and it is predicted that it will be at least five to ten years before solar cells that take advantage of the phenomenon are produced. Engineering processes also provide an obstacle for the researchers working on the project. Once suitable materials for singlet fission are discovered, the next step is working out how to incorporate them into a working solar panel that actually produces electricity. Currently the only working singlet fission panels have an efficiency of just 2 to 3 percent.
Bardeen remains confident in the face of these hurdles though, stating that the existing singlet fission panel proves that it can be done.