The first step in efficiently converting sunlight into electricity or other forms of energy is to install an effective light-harvesting system. Ideally, this should be panchromatic, meaning it absorbs the whole visible spectrum
Plants and bacteria have light-collecting antennae that serve as models for this. They collect a wide range of light for photosynthesis, but their structure is extremely complex, requiring several dyes to transport the energy of the absorbed light and focus it on a focal spot.
Human-developed light-harvesting systems have downsides as well.
Despite being panchromatic, inorganic semiconductors, such as silicon, absorb light only weakly. To absorb enough light energy, solar cells require very thick layers of silicon in the micrometer range, making them relatively large and heavy.
Organic dyes suited for solar cells are substantially thinner, with layer thicknesses of only about 100 nanometers. However, they have a limited ability to absorb a wide spectral range and, hence, are inefficient.
A thin layer absorbs a large amount of light energy
Researchers at Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, have described in the journal Chem a new light-harvesting system that differs dramatically from prior methods.
“Our system’s band structure is similar to that of inorganic semiconductors. This implies that it absorbs light panchromatically throughout the visible spectrum. Additionally, it makes use of organic dyes’ high absorption coefficients. As a result, it can capture a large amount of light energy in a thin layer, much like natural light-harvesting systems,” says JMU chemistry professor Frank Würthner. His team from the Institute of Organic Chemistry / Center for Nanosystems Chemistry designed and investigated the light-harvesting system at JMU in collaboration with Professor Tobias Brixner’s group from the Institute.
Four Dyes in an Ingenious Arrangement
Simply put, Würzburg’s revolutionary light-harvesting antenna is made up of four different merocyanine dyes that are folded and packed tightly together. The elaborate arrangement of the molecules allows for extremely quick and efficient energy transfer within the antenna.
The researchers have named the prototype of the novel light-harvesting technology URPB. The letters represent the light wavelengths absorbed by the antenna’s four dye components: ultraviolet (U), red (R), purple (P), and blue (B).
Proven Performance Through Fluorescence
The researchers demonstrated the effectiveness of their unique light-collecting technology by evaluating the fluorescence quantum yield. This entails determining how much energy the system emits in the form of fluorescence. This allows us to draw judgments about how much light energy it has previously collected.
As a result, the system transforms 38% of the irradiation light energy throughout a wide spectral range into fluorescence, whereas the four dyes alone convert less than 1% to a maximum of 3%. The appropriate composition and spatial arrangement of dye molecules in the stack thus have a significant effect.
Reference : https://www.sciencedaily.com/releases/2024/06/240626152221.htm