Singlet Fission: The Riddle Of The Missing Energy In Solar cells – Resolved

The performance of solar cells can be enhanced by utilizing a phenomenon known as singlet fission. A group of scientists at Linköping University, Sweden, has solved the issue of energy losses during the reaction. These scientists discover where the missing energy goes during the reaction. Cell Reports Physical Science has published the outcomes of this study. 

Solar energy is an eco-friendly and fossil-free source of electricity. The silicon-based photovoltaic cells at most use 1/3rd of energy in sunlight and convert it to electricity. The sun’s beams consist of photons (packets of light), and these photons consist of energy that is either too high that a portion of the energy is dissipated to waste heat or too low to be absorbed by the solar cell. This maximum theoretical efficiency is known as the Shockley-Queisser limit, while in practice, the efficiency of modern solar cells is 20-25%.

Singlet Fission Phenomenon

The phenomenon of singlet fission in molecular photophysics can allow high-energy photons to be used and converted to electricity without heat loss. Additionally, more scientists’ stars focusing on this phenomenon, and trying to develop the optimal material. Until now, it is challenging to design such material due to unexplained energy losses during singlet fission. Scientists have not been able to recognize the source of these energy losses.

Scientists at Linköping University, together with associates in Barcelona, Cambridge, Donostia, and Oxford have identified where the energy goes during singlet fission.

According to Yuttapoom Puttisong, senior lecturer at Linköping University, singlet fission is very difficult to measure as it takes place in less than a nanosecond. Our study allows us to open the black box and observe where the energy goes during the reaction. Therefore, we will be able to optimize the material to enhance the productivity of solar cells. 

Part of the energy escapes in the form of an intermediate bright state, and this is an obstacle that must be resolved to obtain efficient singlet fission. The determination of energy losses is a significant step to achieve higher solar cell efficiency — from the current 33% to over 40%.

The refined magneto-optical transient process has been used by scientists to recognize the position of energy loss. This method has specific advantages as it can check the ‘fingerprint’ of the singlet fission reaction at a nanosecond timescale. A monoclinic crystal of a polyene, diphenyl hexatriene (DPH), was used in this research. 

However, this new method is used to analyze singlet fission in a more general material library. 

singlet fission of the magneto-optic instrument
View from the inside of the magneto-optic instrument. Credit: Thor Balkhed

Yuqing Huang is a former doctoral scholar in the Department of Physics, Chemistry, and Biology at Linköping University, and the leading author of the study now published in a newly established publication, Cell Reports Physical Science:

“The original process is carried out in the crystalline material. If we can enhance this material to grasp the energy from the singlet fission, we will be significantly closer to use in practice. Additionally, the singlet fission elements are economical to produce and suitable for integration with existing solar cell technology,” says Yuqing Huang.

Reference: “Competition between triplet pair formation and excimer-like recombination controls singlet fission yield” by  Yuqing Huang, Chanakarn Phansa, William K. Myers, Maria E. Sandoval-Salinas, Irina A. Buyanova, David Casanova, Weimin M. Chen, Yuttapoom Puttisong,Akshay Rao, and Neil C. Greenham 8 February 2021, Cell Reports Physical Science.
DOI: 10.1016/j.xcrp.2021.100339

The study has been backed mostly by the Swedish Research Council and the Knut and Alice Wallenberg Foundation.

Footnote: A nanosecond is a billionth of a second.

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