There are, however, another side to the recovery in this type of light. Solar cells are effective in the infrared, but they lose much of the available energy of the most energetic photons in the visible portion of the spectrum.
When a photon is absorbed, it creates a single electronic excitation (exciton), which is then separated into an electron and a positively charged hole, regardless of the light energy. One way to improve efficiency would be to divide by 2 the available energy from the visible photons, which leads to a doubling of the current in the solar cell.
Researchers at Cambridge and Mons studied the process by which the initial exciton can be divided into one pair of half-power. This can occur in some organic molecules when the quantum mechanical effect of the electron motion in a fixed state of ‘Singlet initial double the energy in organizing the’ triplet ‘.
The study, published in the journal ‘Nature Chemistry’, shows that this process of fission of ‘singlet’ in pair of ‘Triplet’ depends on the ultra-sensitive interactions between molecules. By studying the process of molecular solution, it is possible to control when this process is started.
When the material is very dilute, the distance between molecules is large, the singlet fission therefore can not occur. When the solution is concentrated, collisions between molecules are more frequent. The researchers found that the phase of fission occurred when two of these molecules were in contact, and remarkably, the fission of the singlet is then completely effective, so that each photon produces two triplets.
This study sheds new light on the fundamental processes of fission ‘Singlet’ which demonstrates its understanding and its use could greatly improve solar cells. Chemists will be able to use these results to produce new materials, the team said the Cavendish Laboratory (Cambridge), who is currently working on ways to integrate these solutions in some devices.
“We started back to basics, looking at the challenge of solar energy from a perspective of blue sky,” said Dr. Brian Walker, a researcher belonging to the optoelectronic group of the Cavendish Lab, and has led the study.
“The fission ‘Singlet’ offers a route to boost the efficiency of solar cells using low cost materials. We are only beginning to understand how this process works, and the more we learn and we expect technological improvements ahead. ”
The team used a combination of laser peak experiences – which measure time with extreme precision – with chemical methods used in the analysis of reaction mechanisms. This dual approach has allowed researchers to slow down the fission and observe a key intermediate step, never observed.
“Very few laboratories in the world have as versatile as our laser device in Cambridge,” said Andrew Musser, another researcher who worked on the study. “This allowed us to get closer to accurately observe how the fission of ‘Singlet’ occurred step.”