Innovative Design: A team of chemists has developed a novel light-harvesting system that could make solar energy utilization even more efficient in the future. They used four photoactive dyes, stacked similarly to the photosynthetic pigments found in the cellular organelles of plants and bacteria. This combination allows the dyes to absorb a substantial amount of light.
Electricity from sunlight is a crucial pillar of the energy transition. Therefore, solar installations are expected to be continuously expanded in the coming years. Various devices in our daily lives already convert solar energy into other forms of energy. Most photovoltaic systems contain semiconductors like perovskite or silicon, which absorb a significant portion of the visible light spectrum and convert it into electrical energy. However, perovskite has poor durability, and silicon systems are not particularly efficient.
To capture enough light energy, several layers of silicon are stacked in the panels, making the solar cells bulky and heavy. A much slimmer and lighter alternative would be organic solar cells based on photoactive dyes. However, these do not absorb the entire light spectrum and are also not very efficient.
Nature-Inspired Dye Mix A team led by Alexander Schulz from the University of Würzburg has now developed a new light-harvesting system that bypasses these shortcomings. The chemists designed a molecular complex inspired by the light-harvesting antennas of plants and bacteria. These antennas capture a broad light spectrum for photosynthesis, channel the energy internally, and focus it on a central point. This is made possible by a complex and evolutionarily optimized structure comprising many different pigments, including chlorophylls, carotenoids, and bilins.
Similarly, the new light-harvesting system by Schulz and his colleagues is constructed. It consists of four different merocyanine dyes embedded in a zigzag folded peptide framework, tightly stacked. This molecular arrangement allows for rapid energy transport within the system. Additionally, the four dyes absorb ultraviolet (U), red (R), violet (P), and blue (B) light, covering a broad spectrum of wavelengths from 500 to 700 nanometers. Accordingly, the researchers named their prototype URPB.
High Efficiency with Coupled Dyes To determine the efficiency of their artificial antenna, Schulz and his colleagues measured how much excess energy the system emits as fluorescence. This allows conclusions about the amount of light energy previously collected. The dye combination converts 38 percent of the incoming light energy into fluorescence, as reported by the chemists. Individually, however, the four dyes each achieve a maximum of three percent.
The spatial arrangement of the dyes in the stack allows for chemical interactions between the individual molecules, making the system more efficient. This could make future solar cells more powerful and thus enable a higher yield of electricity in photovoltaics.
“The Best of Both Worlds” According to the researchers, their technique combines the best of both worlds: “Our system has a band structure similar to that of inorganic semiconductors. Thus, it absorbs across the entire visible range,” explains senior author Frank Würthner. “And it utilizes the high absorption coefficients of organic dyes. This allows it to capture a large amount of light energy in a relatively thin layer, similar to natural light-harvesting systems.”