Generate more electrical energy from solar cells and conduct further research on so-called singlet fission. This is part of a joint research project currently underway by scientists from Friedrich-Alexander-Erlangen-Nuremberg University (FAU), which is in collaboration with Argonne at Northwestern University Evanston- Northwest Solar Energy Research Center (ANSER). Singlet fission can greatly improve the efficiency of solar cells-thanks to the latest research, it is one step closer to being possible. These findings were published in the scientific journal "Chemistry".
Global energy consumption is growing rapidly, and this upward trend will continue in the coming years. In order to meet the demand while protecting the environment, renewable energy sources such as solar energy, wind energy, water energy and biomass energy are becoming more and more important. However, only about 6% of Germany ’s total power generation in 2017 came from photovoltaic systems, and our existing silicon-based technology is quickly reaching the limit of potential.
Silicon-based photovoltaic technology is rapidly reaching the limit of its potential (picture from the network)
Use solar cells to generate electricity
Solar cells are extremely inefficient at converting solar energy into electrical energy. Their current efficiency is only 20% to 25%. There is a call for new methods to significantly improve the performance of solar cells and generate more electricity. The answer may be found in the process of physical chemistry, which will greatly improve the efficiency of solar cells. Scientists at the FAU and ANSER centers have been exploring a promising method as part of their joint research project in the Emerging Fields Project (EFI). The researchers studied the so-called singlet fission (SF) mechanism, in which one photon excites two electrons.
Have a better understanding of singlet fission
The principle of single-line fission was discovered about fifty years ago, but its potential to significantly improve the efficiency of organic solar cells was recognized by American scientists only ten years ago. Since then, researchers around the world have been working on a deeper understanding of the basic processes and complex mechanisms behind it. Professor Michael Wasielewski from the ANSER Center, researchers from FAU-Professor Dirk Guldi, Chairman of Physical Chemistry, Professor Rik Tykwinski (University of Alberta, Canada), Chairman of Organic Chemistry, Dr. Michael Thoss (Albert-Ludwigs-Universität), Professor of Theoretical Solid State Physics Freiburg) and Professor Tim Clark of the Computer Chemistry Center (CCC) are now trying to clarify some very important aspects of singlet fission (SF).
Detailed understanding of the process
When a photon from sunlight encounters and is absorbed by a molecule, the energy level of an electron in the molecule increases. By absorbing photons, the organic molecules thus change to a high energy state. The solar cell can then use this energy temporarily stored in the molecule to generate electrical energy. The best solution for traditional solar cells is that each photon generates an electron as a carrier of electrical energy. However, if a dimer of the selected compound is used, two electrons from adjacent molecules can be converted into a higher energy state. In general, a photon will produce two excited electrons, and these two electrons can be used to generate current. This process is called singlet fission (SF), which can greatly improve the performance of solar cells under ideal conditions. The chemists and physicists at the FAU and ANSER centers have studied the underlying mechanism in more detail, thus gaining a broader understanding of the SF process.
Singlet fission (SF) is the process of converting a single excited state into two triplets.
Three important findings
As a first step in research, scientists produced a molecular dimer from two pentene units. This hydrocarbon is considered to be a promising option for the use of singlet fission in solar cells. They then exposed the liquid to light and used various spectroscopic methods to study the photophysical processes within the molecule.
This gave the researchers three profound insights into the mechanism of singlet fission in the molecule. First, they successfully proved that coupling to a higher charge transfer state is essential for efficient SF. Second, they verified the singlet fission model they created and published recently (doi: 10.1038 / ncomms15171). The third and final item, they proved that the SF efficiency is obviously related to the coupling strength of the two pentene subunits.
The researchers' findings demonstrate the importance of carefully planning the design of SF materials. This is an important milestone in generating electricity using SF-based photovoltaic systems. However, to achieve or approach practical applications, further basic research is still required.
(Originally from: Daily Science China New Energy Network Synthesis)
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