Scientists develop innovative system to harvest light efficiently

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Converting sunlight into electricity or other forms of energy starts with an efficient light-harvesting system.

Ideally, this system should absorb the entire spectrum of visible light, a feature known as being panchromatic.

Nature provides a great model for this in the light-collecting antennae of plants and bacteria.

These natural systems capture a broad spectrum of light for photosynthesis, but they are complex and require many different dyes to transfer the absorbed light energy to a central point.

Human-made light-harvesting systems also have their own problems:

  • Inorganic semiconductors, like silicon, are panchromatic but absorb light weakly. To capture enough light energy, they need very thick layers of silicon, making solar cells bulky and heavy.
  • Organic dyes are much thinner, with a layer thickness of only around 100 nanometers. However, they don’t absorb a broad range of light and thus are not very efficient.

Researchers at Julius-Maximilians-Universität (JMU) Würzburg in Bavaria, Germany, have developed a new light-harvesting system that stands out from previous systems. Their findings were published in the journal Chem.

“Our system has a band structure similar to that of inorganic semiconductors. This means it absorbs light across the entire visible range. And it uses the high absorption coefficients of organic dyes. As a result, it can absorb a great deal of light energy in a relatively thin layer, similar to natural light-harvesting systems,” says JMU chemistry professor Frank Würthner.

The innovative light-harvesting system from Würzburg consists of four different merocyanine dyes. These dyes are arranged in a folded, closely stacked manner. This arrangement allows for ultra-fast and efficient energy transport within the system.

The researchers named the prototype URPB, which stands for the light wavelengths absorbed by the four dyes: U for ultraviolet, R for red, P for purple, and B for blue.

To prove their new light-collecting system works well, the researchers measured its fluorescence quantum yield. This measures how much energy the system emits as fluorescence, giving an idea of how much light energy it collected.

The results were impressive: the system converted 38% of the irradiated light energy into fluorescence over a broad spectral range. In comparison, the individual dyes managed less than 1% to a maximum of 3%. The right combination and skillful arrangement of the dye molecules made a big difference.

This new system could lead to more efficient solar cells and other devices that convert sunlight into energy. By combining the benefits of both inorganic semiconductors and organic dyes, the researchers have created a light-harvesting system that is both thin and highly effective. This innovative approach may pave the way for more advancements in the field of solar energy and beyond.