A question of affinity: How to design organic solar cell materials
A collaboration of scientists from the Max Planck Institute for Polymer Research (MPI-P) in Germany and the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia have recently scrutinized organic solar cells and derived design rules for light-absorbing dyes that can help to make these cells more efficient, while tailoring the absorption spectrum of the cells to the needs of the chosen application.
Most of us are familiar with silicon solar cells, which can be found on the rooftops of modern houses. These cells are made of two silicon layers, which contain different atoms such as boron and phosphorus. When combined, these layers direct charges generated by the absorbed sunlight towards the electrodes – this (photo)current can then be used to power electronic devices.
The situation is somewhat different in organic solar cells. Here, two organic materials are mixed together, rather than arranged in a layered structure. They are blends of different types of molecules. One type, the acceptor, likes to take electrons from the other, the donor. To quantify how likely “electron transfer” between these materials takes place, one measures the so-called “electron affinity” and “ionization energy” of each material. These quantities indicate how easy it is to add or extract an electron from a molecule. In addition to determining the efficiency of organic solar cells, electron affinity and ionization energy also control other material properties, such as color and transparency.
By pairing donor and acceptor materials, one creates a solar cell. In an organic solar cell, light-particles (“photons”) transfer their energy to electrons. Excited electrons leave behind positive charges, called “holes”. These electron-hole pairs are then separated at the interface between the two materials, driven by the differences in the electron affinity and ionization energy.
Until now, scientists assumed that both electron affinity and ionization energy are equally important for the solar cell functionality. Researchers from KAUST and MPI-P have now discovered that in many donor-acceptor blends, it is mainly the difference of the ionization energy between the two materials, which determines the efficiency of the solar cell. The combination of results from optical spectroscopy experiments, performed in the group of Frédéric Laquai at KAUST, as well as computer simulations performed in the group of Denis Andrienko, MPI-P, in the department headed by Kurt Kremer, allowed precise design rules for molecular dyes to be derived, aimed at maximizing solar cell efficiency.
“In the future, for example, it would be conceivable to produce transparent solar cells that only absorb light outside the range visible to humans – but then with the maximum efficiency in this range,” says Denis Andrienko, co-author of the study published in the journal “Nature Materials”. “With such solar cells, whole fronts of houses could be used as active surface”, Laquai adds.
The authors envision that these studies will allow them to reach 20 % solar cell efficiency, a target that industry has in mind for cost-effective application of organic photovoltaics.
Wissenschaftliche Ansprechpartner:
Dr. Denis Andrienko
Tel.: +49 6131-379-147
eMail: denis.andrienko@mpip-mainz.mpg.de
Originalpublikation:
Karuthedath, S., Gorenflot, J., Firdaus, Y. et al. Intrinsic efficiency limits in low-bandgap non-fullerene acceptor organic solar cells. Nat. Mater. (2020).
https://doi.org/10.1038/s41563-020-00835-x
Weitere Informationen:
https://www2.mpip-mainz.mpg.de/~andrienk/ – Website of Denis Andrienko
Media Contact
All latest news from the category: Power and Electrical Engineering
This topic covers issues related to energy generation, conversion, transportation and consumption and how the industry is addressing the challenge of energy efficiency in general.
innovations-report provides in-depth and informative reports and articles on subjects ranging from wind energy, fuel cell technology, solar energy, geothermal energy, petroleum, gas, nuclear engineering, alternative energy and energy efficiency to fusion, hydrogen and superconductor technologies.
Newest articles
Integrated light as a key to future computers
While computer chips are getting smaller and faster every year, one challenge remains unsolved: combining electronics and photonics on a single chip. Although components such as micro LEDs are available…
Speaking without vocal cords, thanks to a new AI-assisted wearable device
The adhesive neck patch is the latest advance by UCLA bioengineers in speech technology for people with disabilities. People with voice disorders, including those with pathological vocal cord conditions or…
Bendable energy storage materials by cool science
Imaging being able to wear your smartphone on your wrist, not as a watch, but literally as a flexible band that surrounds around your arm. How about clothes that charge…