New insight into improving the efficiency of solar cells
Researchers are advancing the efficiency of next-generation solar cells by incorporating a technique that breaks light particles, or photons, into smaller components.
In a study published in Nature Chemistry, scientists investigated the process of singlet fission, in which light particles split, and its underlying mechanisms.
Professor Tim Schmidt from UNSW Sydney’s School of Chemistry, who has been studying singlet fission for more than a decade, suggests that this process could improve the efficiency of current silicon solar cell technologies.
“Today’s solar cells work by absorbing photons which are then drawn to the electrodes to do the work,” says Prof. Schmidt. “But as part of this process, much of this light is lost as heat. Therefore, solar panels do not operate at full efficiency.”
Most photovoltaic solar panels today are made of silicon. Co-author Professor Ned Ekins-Daukes from UNSW’s School of Photovoltaics and Renewable Energy Engineering notes that while this technology is cost-effective, it is approaching its performance limits.
“The efficiency of a solar panel represents the part of the energy provided by the sun that can be converted into electricity,” says Prof. Ekins-Daukes. “The highest efficiency was observed earlier this year by our industrial collaborator LONGi. They demonstrated a silicon solar cell with an efficiency of 27.3 percent,” he says. “The absolute limit is 29.4 percent.”
Prof. Schmidt emphasizes the complexity of understanding how singlet fission works, especially the transformation of one photon into two. “Our study focuses on the pathway of this process. And we used magnetic fields for the interrogation. The magnetic fields manipulate the wavelengths of the emitted light to reveal the way singlet fission occurs. And that hasn’t been done before.”
Different colors of light have photons with different energies. Regardless of the energy of the light, the cell receives the same energy, with the excess being converted into heat, explains Prof. Schmidt. “So when you absorb a red photon, there is a bit of heat,” says Prof. Schmidt. “With blue photons there is a lot of heat. There is a limit to the efficiency of solar cells.”
Introducing singlet fission could significantly increase the potential of silicon cells. “Introducing singlet fission into a silicon solar panel will increase its efficiency,” says Prof. Ekins-Daukes. “This allows a molecular layer to supply additional power to the panel.” The process breaks the photon into smaller energy units that can be used individually, maximizing the higher energy part of the spectrum and reducing heat loss.
Last year, the Australian Renewable Energy Agency (ARENA) selected UNSW’s singlet fission project for their Ultra Low Cost Solar program. This initiative aims to develop technologies that achieve efficiency of more than 30 percent by 2030 at a cost of less than 30 cents per watt. The team used a single-wavelength laser to excite the singlet fission material and applied magnetic fields with an electromagnet to slow the process, making it easier to study.
“With this solid scientific understanding of singlet fission, we can now prototype an improved silicon solar cell and then work with our industrial partners to commercialize the technology,” says Prof. Ekins-Daukes. “We are convinced that we can obtain silicon solar cells with an efficiency of more than 30 percent,” says Prof. Schmidt.
Research report:Magnetic fields reveal signatures of triplet-pair multi-exciton photoluminescence in singlet fission
