New light-harvesting system offers 38% more efficiency for solar cells

Researchers at the Julius-Maximilians-Universität (JMU) in Würzburg, Germany, have designed a novel light-harvesting system that can more efficiently use solar energy by absorbing the entire visible light spectrum. When tested in a research environment, their system converted 38 percent of incident light into fluorescence, a significant leap compared to other systems today.

Technologies such as solar energy are critical in our bid to move away from fossil fuels. Although solar energy is making global gains in terms of installations, the technology has plenty of scope for improvement in terms of energy efficiency.

Interesting Engineering has previously reported on how researchers are using various approaches to improve the output generated by a solar cell.

While most of this has focused on the material used to make the solar cell, researchers at JMU looked at the problem from a different angle—the light-harvesting system in solar cells.

Issues with light-harvesting systems

The light-harvesting systems used in commercially available solar cells are not very efficient.

They are made from inorganic semiconductor materials such as silicon, and although they are panchromatic and able to absorb the entire spectrum of visible light, their absorbance is very low.

This is why solar cells need thick silicon layers to absorb more light, making them heavy.

The researchers were inspired by naturally occurring systems, such as plants and bacteria, which can use a broad spectrum of light for photosynthesis .

This is achieved using organic dyes, which are much thinner and lighter. When used alone, the organic dyes do not absorb light across a wide spectral range.

The researchers then tried to replicate the complex arrangement of dyes in naturally occurring systems to develop a highly efficient new light-harvesting system.

How does the system work?

The JMU researchers designed a light-harvesting antenna using four different merocyanine dyes. These dyes were folded and stacked upon each other sophisticatedly, allowing ultra-fast and efficient energy transport.

The prototype light-harvesting system has been dubbed URPB after the wavelengths that the four dye components can absorb – U for ultraviolet, R for red, P for purple, and B for blue.

To determine how well the light harvesting system performed, the researchers measured its fluorescence quantum yield – the amount of energy the system emits in the form of fluorescence, the press release said.

The team found that in their special arrangement, the four dyes generated fluorescence from the 38 percent of light incident on them. In comparison, when placed individually, each dye could only convert no more than three percent of the light into fluorescence, showcasing the significant difference the spatial arrangement of dyes makes.

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

The research findings were published in the journal Chem .